Journal of Medical Physics
 Home | Search | Ahead of print | Current Issue | Archives | Instructions | Subscription | Login  The official journal of AMPI, IOMP and AFOMP      
 Users online: 223  Home  EMail this page Print this page Decrease font size Default font size Increase font size 

 Table of Contents    
Year : 2017  |  Volume : 42  |  Issue : 5  |  Page : 110-255


Date of Web Publication24-Oct-2017

Correspondence Address:
Login to access the Email id

Source of Support: None, Conflict of Interest: None

Rights and PermissionsRights and Permissions


How to cite this article:
. Poster. J Med Phys 2017;42, Suppl S1:110-255

How to cite this URL:
. Poster. J Med Phys [serial online] 2017 [cited 2023 Feb 6];42, Suppl S1:110-255. Available from:

   P-1: Intensity Modulated Radiotherapy Plan Verification For Different Dose Rates and Different Grid Sizes Using Fluence Measurement Top

Rahil Anjum, C. Varatharaj, M. Ravikumar, K. M. Ganesh, S. Sathiyan, B. Shwetha

Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India. E-mail: [email protected]

Introduction: The principle of Intensity Modulated radiotherapy (IMRT) is to deliver a high dose to the target volume and an acceptably low dose to the surrounding normal structures. Thus choosing an optimum grid size plays a vital role for planning in radiotherapy cases especially while treating with IMRT. A minimal change of even 1 mm of grid size can result in large variation in the treatment planning. The aim of this study is to find the optimal IMRT plan by comparing the IMRT pre-treatment Quality Assurance (QA) verification plan for different dose rates (300, 400, 500 and 600 MU/min) and for different grid sizes (2.5 and 5 mm) using fluence measurement in a 2D array (I'MatriXX).

Materials and Methods: 20 patients (10 Brain and 10 Head and Neck cases) are planned for the IMRT and the verification plans are created for different dose rates and for different grid sizes in the Treatment Planning System (TPS) for each patient. The totals of 160 verification plans are created, Clinac 2100-DHX linear accelerator and I'MatriXX are used for the execution of the verification plans. All the 160 verification plans were executed and the obtained data for all the plans is saved in the PC for the later analysis. The obtained data is analysed between the TPS obtained dose plane and the measured dose plane using the OmniPro I'mRT software.

Results and Discussion: In our study, the correlation coefficients were calculated for TPS v/s I'MatriXX and the values lie between 0 and 1. The quantitative analysis between the calculated and measured dose distribution was evaluated using Distance to Agreement (DTA) and Gamma-index. The tolerance of 3% dose difference and 3 mm DTA and Gamma tolerance ≤1 was set for the analyses. In our results there is no significant change in mean coefficient of variation between the measured fluences v/s TPS calculated data in all brain and H and N cases. The variation in percentage of pixels passing gamma also found that there is no significant changes with respect to grid size of 2.5 mm and 5 mm of different dose rates in both brain and head and neck cases. We observed lower passing rate of DTA in head and neck cases and which is similar in grid size variation and also with respect to dose rates. Similar work published by other researchers using portal dosimetry was found that, there was a significant change in passing rate due to dose rate change, but in our case we found that, which is insignificant. This could be because of finite size of the ionization chamber and the spacing between the chambers in I'MatriXX device where as the resolution in portal imaging device is better and having finite pixel size in the portal imaging devices.

Conclusion: The qualitative analysis using comparison of profile and isodose lines were found to be insignificant change between the calculated and measured fluences. The quantitative analysis was done using gamma evaluation method and finding the correlation coefficient. Based on the our obtained data analysis we could not found much difference between the measured and calculated fluences both in terms of qualitative and quantitatively for change in dose rate and grid sizes. Hence, we conclude that, this could be due to the volume average effect of finite size of the detectors in the I'MatriXX and the finite spacing between the detectors.

   P-2: Reduction Method Of the Skin Surface Dose in Megavoltage Photon Radiotherapy Top

Masahiko Okumura, Mikoto Tamura1, Hajime Monzen1,2, Kenji Matsumoto, Masakazu Otsuka1, Kohei Hanaoka, Kohei Shimomura3, Yasumasa Nishimura3

Department of Central Radiology, Kindai University Hospital, 1Department of Medical Physics, Graduate School of Medical Science, Kindai University, 2Department of Radiation Oncology, Faculty of Medicine, Kindai University, Osaka, 3Department of Radiological Technology, Faculty of Medical Science, Kyoto College of Medical Science, Nantan, Japan. E-mail: [email protected]

Introduction: Many kinds of carbon couches are commonly used in megavoltage radiotherapy to provide patient support. However, the carbon couch causes the increase of surface dose due to shifting the depth dose profile to the patient surface, which is associated with skin toxicity.

Objectives: A novel rigid couch (HM board) constructed from polycarbonate foam core sandwiched by two thin layers of glass fiber has been developed. In this study, we evaluated the increase or decrease of surface dose with various tools on the carbon couch and verified whether the HM board was able to reduce the surface dose compared to the carbon couch in megavoltage photon radiotherapy.

Materials and Methods: We measured the absorbed surface doses with comfort tools (cloth mat and 5 cm Styrofoam board) and immobilization device (vacuum-fixed cushion) on a carbon couch (iBeam Couchtop STANDARD; BrainLab) and H-M board alone for 6 and 10 MV photon beams by a plane-parallel ionization chamber. The prescribed dose at 5.0 cm depth in solid water phantom (SCD = 100 cm) was 2.0 Gy with a field size of 10 × 10 cm2. We also measured the depth dose profiles for 6 and 10 MV photon beams with various thickness of the Styrofoam board on the carbon couch and the H-M board alone.

Results and Discussion: The absorbed surface doses were 2.209, 2.200, 2.169, 2.079, and 2.027 Gy for the carbon couch alone, with cloth mat, vacuum-fixed cushion, and 5 cm Styrofoam board on the carbon couch, and the H-M board alone, respectively, with 6 MV photon beams. With 10 MV photon beams, the absorbed surface doses were 1.980, 1.998, 1.958, 1.823, and 1.741 Gy, respectively. The Styrofoam board on the carbon couch had no impact on the depth dose profile, while the H-M board shifted approximately 0.4 cm to the depth direction compared with the carbon couch alone. The 5 cm Styrofoam board reduced the surface dose by 5–7%. The H-M board, with a tissue equivalent thickness 0.4 cm less than carbon couch, reduced the surface dose approximately 3–4% compared with 5 cm Styrofoam board on the carbon couch. The H-M board could be more useful in clinical situations instead of carbon couch since it provided the sufficient space compared to a couch plus the Styrofoam board in megavoltage photon radiotherapy.

   P-3: Verification Of Intensity Modulated Radiation Therapy Treatment Using Fluence Map Reconstructed from Varian Linac Log Files Top

Nur Shaheera Midi, Hafiz Mohd Zin

Oncology and Radiological Sciences Cluster, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Bertam, Penang, Malaysia. E-mail: [email protected]

Intensity Modulated Radiation Therapy (IMRT) delivers highly conformal dose to the tumour using dynamic multileaf collimator (dMLC). The dMLC moves continuously at variable speed during treatment and is prone to delivery errors. Pre-treatment verification of IMRT ensures accurate delivery of the treatment planned. The study develops computer algorithm to analyse treatment log files from a Clinac iX linac with 120 MLC leaves (Varian Medical Systems, Palo Alto, CA). Varian log file records the prescribed and delivered MLC leaves position and other linac parameters at 20 Hz. The algorithm reconstructs the IMRT dose delivered and calculate errors between the planned and the actual IMRT treatment. Dose reconstruction and analysis were performed using Matlab (MathWorks, Natick, MA). Five clinical IMRT cases were evaluated in this study. The MLC speed ranged from 1.6 cm per second to 4.0 cm per second. Using gamma index at 3% dose difference and 3 mm distance to agreement (DTA) to compare between the planned dose map and delivered dose map, all cases obtained 100% pass rate. Application of the log file in verification of dMLC based radiotherapy delivery is useful and can be used as supplementary data in dosimetry based IMRT pre-treatment check. Acknowledgement: This work is funded by Fundamental Research Grant Scheme, Ministry of Education Malaysia, 203/CIPPT/6771383. The authors would like to acknowledge LF Chin for his preliminary work for this study and LC Lim for providing log files in this work.

   P-4: Investigation On The Feasibility of Using CBCT (Cone Beam Computed Tomography) as a Readout Tool for NIPAM Polymer Gel Dosimetry Top

Winfred Michael Raj, S. Ebenezer Suman Babu, K. Mohamathu Rafic

Department of Radiotherapy, Christian Medical College, Vellore, Tamil Nadu, India. E-mail: [email protected]

Introduction: The post readout of polymer gel is often performed by various imaging modalities such as MRI, and X-Ray CT. Since, these imaging modalities are not easily available due to patient load and also involves significant time for imaging, in this study, we have investigated the feasibility of using a CBCT scanner that makes use of a cone beam of X-ray to read out the NIPAM (N-Isopropylacrylamide) polymer gel dosimeter.

Aim and Objectives: To assess the feasibility of using CBCT scanner as a readout tool for analyzing the NIPAM polymer gel. (1) To investigate the dose readout capability of an On-Board Imaging Cone Beam Computed tomography (CBCT) setup to read and quantify the change in Hounsfield Units due to polymerization in a NIPAM gel dosimeter. (2) To remove noise in the recorded dose information. (3) To develop a MATLAB code that quantifies the Hounsfield for different region of interests in a CBCT image. (4) To quantify the amount of polymerization by measuring the change in Hounsfield Units with respect to the dose in a NIPAM gel dosimeter.

Materials and Methods: The polymer gel dosimeters in this study are co-solvent free and the recipe is as proposed by chain et al with increased sensitivity and resolution for X-Ray CT dose response. The NIPAM gel dosimeter was prepared by soaking and dissolving gelatin, by stirring for about 1 hour. Once the gelatin is completely dissolved and the solution becomes clear, the gelatin solution is cooled down and NIPAM and the cross linker (Bis) after which, the oxygen scavenger (THPC) is added (5 mM) and it is stirred for about 30 seconds.

Initially the dose signal build-up time was analyzed in the irradiated gel and the time taken for the polymerization process to complete is found, following which the gel dosimeters irradiated for different known doses are read out using a CBCT, and the change in density is quantified by analyzing the Hounsfield units across the irradiated region for which a separate Matlab code was developed.

A separate MATLAB code was developed to average the images slice by slice, to reduce noise and to increase the signal to noise ratio in the irradiated gel.

Results and Discussions: The exclusive study on the buildup shows that complete dose signal development is achieved after 10 hours of irradiation and the gel dosimeter can be readout any time after that.

In our study, the effect of image averaging was found to be close to what was proposed by Hilts et al. Image averaging filter used in our study was found to be effective in gel dosimeters with and without dose. A very high increase in the SNR could be seen as a result of averaging.

The NCT values that are calculated from the Average HU values that are measured in four different Regions of Interest (10 x 10 mm2, 8 x 8 mm2, 6 x 6 mm2, and 4 x 4 mm2) are found to be linear as proposed by Johnston et al.

   P-5: Generation of Magnetic Resonance Image with Teeth Restorations from Computed Tomography Segmentation Top

Min-Young Lee, Kyu-Ho Song, Bo-Young Choe, Tae-Suk Suh

Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Korea. E-mail: [email protected]

Introduction: The purpose of this study was (a) to develop a CT/MR oral phantom and design containers with insertable dental implants; (b) to optimize the parameters for metal artifact reduction by a multi modal system; and (c) to register CT/MR to generate non-artifact MR images with dental restorations.

Materials and Methods: The phantom comprises sphere which shaped to simulate the anatomical structures of a human head with real teeth and dental implants. All measurements were done using a human 3T MRI with spin echo (SE) and gradient echo (GRE) sequences image scan together with CT high resolution image. Firstly, the metal regions and normal teeth parts are extracted with a suitable threshold from an initial image reconstructed without metal artifacts reduction from the CT images. Secondly, corrected metal projection regions of MR images and finally, CT images are applied into artifact-reduced MR images.

Results: The dedicated CT/MR phantom was performed to assess the magnitude and spatial dependence of MR image geometrical distortion and CT artifact accuracy in various sequences. After CT/MR registration, spin echo sequence presented 12.0 mm and 24.0 mm differences in X and Y axes and gradient echo sequence showed 18.0 mm and 36.6 mm differences in X and Y axes.

Discussion: The dedicated phantom provides a unique and useful tool in head and neck research in offering references of metal artifact reduction and registration methods for multi-modality medical images. Therefore, the contrast-enhanced dental MR image offers a means of visualizing the different anatomical structures in diagnostic system.

   P-6: The Evaluation of Gamma Index for EPID Based Portal Dosimetry with Process Capability Analysis in Patient-Specific Volumetric Modulated Arc Therapy Quality Assurance Top

Samju Cho, Rena Lee, Chunhee Lee, Minsoo Chun, Sohyun Ahn1, Suk Lee2, Kyubo Kim

Department of Radiation Oncology, Ewha Womans University Medical Center, 1Department of Radiation Oncology, College of Medicine, Yonsei University, 2Department of Radiation Oncology, College of Medicine, Korea University, Seoul, Korea. E-mail:

Introduction: Electronic portal image device (EPID) based portal dosimetry is wildly used for Patient-specific volumetric modulated arc therapy (VMAT) Quality Assurances (QA). The Gamma pass index and rate to ensure the VMAT are 3 mm/3% and 95% at our institution. However, errors could be made if the gamma indexes are based on 3 mm/3% due to the large error tolerance during the complex radiation therapy process.

Objectives: The purpose of this study is to establish appropriate patient-specific QA gamma index with process capability analysis using a method of statistical process control (SPC) for the VMAT portal dosimetry.

Materials and Methods: The recent 43 data patient-specific QA cases using the portal dosimetry (PD) were selected in this study. The patient-specific QA, sorted from gamma criteria respectively, were analysed retrospectively using a method of statistical process control (SPC). The values of gamma indexes were 3 mm/2%, 2 mm/3%, 2 mm/2%, 2 mm/1.5%, 1.5%/2 mm, 2 mm/1% and 1 mm/2% in comparison to our institution's standard value of 3 mm/3%. The first 20 cases were selected in order to set up accurate control limits for SPC analysis, and were analysed with the control limits. We compared each process capability index (PCI) using the process capability analysis of the GPR with the gamma index.

Results: The analysed PCI values with respect to gamma indexes were calculated to be 0.89 for 3 mm/3%, 1.07 for 3 m/2%, 0.91 for 2 mm/3%, 1.11 for 2 mm/2%, 1.16 for 2 mm/1.5%, 1.12 for 1.5 mm/2%, 1.2 for 2 mm/1% and 1.15 for 1 mm/2%. The mean gamma pass rate were 98.9% for 3 mm/3%, 97.1% for 3 m/2%, 97.6% for 2 mm/3%, 95.1% for 2 mm/2%, 92.6% for 2 mm/1.5%, 92.8% for 1.5 mm/2%, 89.2% for 2 mm/1% and 88.5% for 1 mm/2%.

Conclusions: The PCI at a gamma index of 3 mm/3%, which is currently used at our institution, appeared to be the lowest and the process capability index was the highest at gamma index of 2 mm/1%. The gamma index of 3 mm/3% for patient-specific QA could be considered to have an unstable process factor as process capability indices over 1.0 are considered to be relatively stable. The PCI values tend to increase as the values of gamma index decline according to the results. The GPR value of 1.2 applied with gamma index of 2 mm/1% was the highest among the results and is considered to be a relatively stable process for our institution with EPID based portal dosimetry.

Acknowledgement: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2015R1D1A1A01060463) and the Radiation Safety Research Programs (1305033) through the Nuclear Safety and Security Commission.

   P-7: Evaluation of EBT3 Film Dosimety Using Dual-Channel Merged Method for Stereotactic Body Radiotherapy Quality Assurance Top

Sang-Won Kang, Jin-Beom Chung1, Kyeong-Hyeon Kim, Keun-Yong Eom1, Jeong-Woo Lee2, Yong-Jin Kim, Tae Suk Suh

Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, 2Department of Radiation Oncology, Konkuk University Medical Center, Seoul, 1Department of Radiation Oncology, Seoul National University Bundang Hospital, Seongnam, Korea. E-mail: : [email protected]

Introduction: This study assessed the feasibility of a dual-channel (DC) merged method for film dosimetry. The red channel (RC) is usually used to ensure dosimetric quality using a conventional fraction dose because the RC is more accurate at low doses within 3 Gy than the green channel (GC). However, the RC is prone to rapid degradation of sensitivity at high doses, while degradation of the GC is slow. Thus, in this study, we designed the dual-channel (DC) merged method which was merged RC and GC dose measurement according to dose ranges.

Objectives: The purpose of this study is to verify the dual-channel (DC) merged method on EBT3 film dosimetry for stereotactic body radiotherapy (SBRT).

Materials and Methods: The film calibration was performed in doses ranging from 0 to 15 Gy with 6-MV photon beams at the 10 × 10 cm2 field. The single channel net-optical density (net OD) was obtained with the measured film for each red and green channels (RC and GC). To acquire the merged net OD of DC, the net ODs of RC and GC were combined at 6, 8, and 10 Gy dose level. To compare the RC, GC and DC, the several SBRT treatment plan cases were applied and measured by EBT3 film. The calculated and measured dose distributions were evaluated with root-mean-squares-error (RMSE) and gamma analysis.

Results and Discussion: For RMSE value of each channels, the RC is more accurate than GC for low doses when comparing the calculated dose distribution, while the RC is more accurate in higher doses than 8 Gy. The accuracy of DC was increased than the RC regardless of low and high doses. For the gamma passing rate with acceptance criteria of 3%/3 mm and 2%/2 mm, all plans for each channel met agreement more than 94% and 84%, respectively. Within the 3%/3 mm gamma criteria, the mean passing rate (97.48%) of DC method was the highest when comparing with single channel method such as the RC (97.42%) and GC (96.92%).

The DC method devised in this study will be more suitable in clinical radiation therapy, especially the dosimetric QA (DQA) for SBRT using high doses. In general, the result of DQA for SBRT is evaluated using the RC with the pretreatment QA plan downgraded for prescription dose. However, this downgraded evaluation has difficulty in reflect real clinical practice due to affect in variation of dose distribution and dose rate in pretreatment QA plan by dose degradation. Our DC method does not necessary need a dose downgrade for pretreatment QA plan. DQA is practical in the real clinical application. Therefore, we recommend the use of DC method in DQA using film dosimetry, especially in high dose treatments, such as SBRT and SRS.

This study found that the DC method has the advantage of reducing single-channel analysis errors in high doses for film dosimetry. Therefore, we recommend that the use of DC method is more appropriate as the dosimetric QA for SBRT using EBT3 film.

   P-8: Phatom Development for Dose Audit of Carbon Ion Raidotherapy Centers in Japan Top

H. Mizuno, A. Fukumura, S. Fukuda, N. Kanematsu, S. Yonai, M. Fukahori, T. Shirai

Department of Charged Particle Therapy Research, National Institute of Radiological Sciences, QST, Chiba, Japan. E-mail: [email protected]

Introduction: In a multi-center clinical trial, it is important to implement a quality assurance program ensure that all centers provide the same dose to patient and achieve high quality trial results. Japan Carbon-ion Radiation Oncology Study Group (J-CROS) was founded in 2014. The purpose of this group is to obtain clinical evidence through multi-center clinical trials among participated facilities to demonstrate the efficiency of carbon ion radiation therapy. In order to implement the quality assurance program from the view point of dose audit it is necessary to prepare auditing tools, especially new phantom.

Objectives: The aim is to develop a phantom suitable for dose auditing. There are many restrictions on the on-site dose measurement. Since it is usually done after patient treatment, the auditing time is limited at the hospital. Quick alignment is required. Furthermore, in order to avoid breakage, it is necessary to attach the chamber easily and safely to the phantom. Of course, the phantom should be easily carried around.

Materials and Methods: Produced phantom was a simple PMMA water tank with ionization chamber holders. The inner side wall of the tank has a groove structure for inserting the ionization chamber holder at every 5 mm depth in a direction towards the horizontal beam axis. Several types of holders were made to support several ionization chamber types such as farmer type, parallel plane type and pinpoint type. We also made an alignment holder with iron ball inside. By using this, we can run end to end tests.

Results and Discussion: The phantom was successfully produced and applied to the dose audit for the J-CROS facilities. Setup time was very short, making the measurement very efficient. Even in the two ionization chamber measurements, one is from the auditor and the other is from hospital, the time loss during ionization chamber exchange was carried out within 2 minutes and setup position was precise. The phantom was also used for the annual dose monitoring as a credentialing for another international multi-center clinical trial.

   P-9: Comparing Dosimetric Parameters of Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Radiation Therapy for Stomach Cancer Top

Sruthy P. Kumar, C. Paranthaman, S. Prabakar, P. Loganathan, Lalitha Kameshwari, David K. Simson, Parveen Alhawat, Harpreet Singh

Department of Radiation Oncology, Action Cancer Hospital, New Delhi, India. E-mail:[email protected]

Introduction: Radiotherapy as an adjuvant treatment plays an important role in the multidisciplinary treatment of gastric cancer. Earlier, with the availability of older radiotherapy techniques the doses delivered to operative bed were high resulting in higher doses to normal surrounding tissues, thus higher toxicities. In modern era of precision radiotherapy, especially with the advent of intensity modulated radiotherapy (IMRT) it has been possible to improve target coverage, at the same time better sparing of organs at risk (OARs). Various modifications have evolved in since the inception of IMRT technique with regard to dynamics of multileaf collimators, such as step and shoot IMRT, dynamic IMRT, and arc-based therapy (VMAT). So far there has been sparse literature on comparison between these techniques. The aim of our research is do a dosimetric comparison between Dynamic IMRT and arc-based therapy (VMAT) techniques.

Materials and Methods: Twenty eight consecutive patients with gastric cancer who underwent adjuvant radiotherapy were enrolled in this study. Two plans were created for each patient, IMRT (7F-IMRT), and VMAT (Double Arc) techniques with Total Prescribed Dose of 45Gy in 25 fractions. The two plans were compared with regard to PTV coverage, doses received by OARs, Homogeneity Index (HI), Conformation Number (CN) and Monitor Units (MUs).

Results and Discussion: There was no statistically significant difference in PTV coverage (D98%, D95%, D50%, D2%, V110%, and V93%) however, CN was significantly better with VMAT (0.871 v/s 0.790; p = 0.050). There was no statistically significant difference in OARs doses (Kidney Dmean, Kidney V18Gy, Small bowel Dmean and Dmax and V15Gy and V45Gy, Spinal cord PRV Dmax, and Pancreas Dmean and Dmax) except liver; liver Dmean and V30Gy being significantly lesser with VMAT (Dmean 18.04 v/s 21.49 Gy; p=0.028 and V30Gy 55.84 v/s 74.82Gy; p=0.036). There was no significant difference in HI between the two plans (p=0.674). There was significantly lesser MUs delivered with VMAT (446.5 v/s 1451.6; p=0.012). The low dose tissue bath (i.e. larger volume of tissues receiving lesser dose) was significantly lesser with VMAT than with IMRT, V10Gy (6379.8 v/s 6778.8cc; sp=0.025), V15Gy (4894.4 v/s 54456.5cc; p=0.012), V20Gy (3724.4 v/s 4102cc; p=0.017), V25Gy (2723.1 v/s 3145.2cc; p=0.017), V30Gy (2040.4 v/s 2427.8cc; p= 0.05).

Thus, from the findings of this research we conclude that VMAT has certain dosimetric advantages over IMRT with regard to liver sparing, CN, MUs delivery and low dose tissue bath. There is no impact of technique used on target coverage, remaining OARs and HI. What implications these dosimetric advantages of VMAT over IMRT have on clinical outcomes and toxicities is yet to be studied. What is certain with our study and few previous studies is that VMAT has advanstages over IMRT in terms of shorter treatment delivery time, thus with a potential to decrease set up errors and patient discomfort. Another advantage of VMAT is the lesser MUs delivered, thus a potential decrease in the incidence of second malignancy by virtue of lesser integral dose, however this is still a hypothesis generating and yet to be verified in clinical studies.

   P-10: Stereotactic Radiotherapy for Pitutary Adenoma: Cyberknife VS Rapidarc Plan Comparison Top

T. K. Bijina1,2, K. M. Ganesh3, B. Subbulakshmi1, A. Pichandi1

1Department of Radiotherapy, Healthcare Global Enterprises, 3Department of Radiation physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, 2Research and Development Centre, Bharathiar University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: Pituitary adenomas are slow growing tumors that arise from pituitary gland and it represents nearly 10% to 15% of intracranial tumors in adults. Radiation therapy is an integral part of postoperative treatment for pituitary adenomas. Stereotactic Radiotherapy (SRT) is a high precision radiotherapy technique which delivers accurate dose to tumor and reduces toxicity to surrounding normal tissues. The objective of the study is to analyze and compare the plan results of Robotic Cyberknife (CK) and Rapidarc (RA) based SRT treatment for pituitary adenomas.

Materials and Methods: Ten patients with pituitary adenoma treated with SRT using CK facility with a dose of 25Gy in 5 fractions planned usingMultiplan4.6treatment planning system (TPS) were taken for the study. CK plans were generated with stepwise multi criteria based sequential optimization using Ray tracing algorithm. Fixed collimators were chosen depending on the target volume. Computed tomography (CT) data sets (slice thickness-1.25 mm) from Multiplan TPS were imported to Eclipse TPS for calculating RA plans. All patients were replanned with RA using Eclipse13.7 for comparison study.

TrueBeam accelerator with 120 multileaf collimator (Varian Medical System, PaloAlto, CA) having 6MV photon energy were used for planning. RA plans were done using noncoplanar arcs (clockwise rotation 181°– 179°; 180.1°–330° with couch 45° and counterclockwise rotation 179.9–30° with couch 315°). RA optimization was performed using Photon Optimizer (PO_13.7.16) and dose were calculated using analytical anisotropic algorithm (AAA_13.7.16) with a grid size of 1.25 mm. Prescription isodose line was chosen such that 95% of the target volume received prescription dose for CK plans whereas dose was normalized in RA plans to achieve same coverage and typical beam arrangements shown in [Figure 1]. The dosimetric parameters evaluated for plan comparison wereD2, D98, Dmax, Naukarma Conformity Index (nCI), Homogeneity index (HI), Dose Spillage Index (DSI75, DSI50 , DSI25) and maximum dose to organ at risk such as brainstem, optic chiasm, optic nerve and eyes.
Figure 1: Rapidarc (with avoidance sector) and Cyberknife (with blocked beams) beam arrangement

Click here to view

Results and Discussion: The median target volume of ten patients was15.15cc (range 2.17cc to 29.09cc). In three cases, the optic nerve dose was restricted to prescription dose since optic nerve was overlapping with target volume. Beam intersection was not allowed through both lens in CK plans whereas avoidance sector were used to limit the dose in RA plans. The dosimetric parameters such as D2, D98 of PTV for CK and RA planswere 28.06 ± 1.00Gy, 27.30 ± 0.58Gy and 24.70 ± 0.2Gy, 24.58±0.32Gy respectively. The maximum dose to PTV in CK plans is higher by 2.5% than RA plans. RA plans showed better conformity 1.38±0.07 as compared to1.31 ± 0.18 in CK. Also, RA plansshowed more homogenous dose distribution than CK plans (10.86 vs13.9). The maximum doses to the brainstem and opticchaism were 20.1 ± 5.30Gy, 22.35 ± 4.73Gy and 20.51 ± 4.26Gy, 22.63 ± 4.71Gyfor CK and RA respectively. The integral dose to the whole brain was3.41 ± 1.61Gy-L for CK plans compared to 3.01 ± 1.10Gy-L for RA plans. Mean MU per fraction was found to be 5332 for CK plans and 1264 for RA plans. Volume receiving 5Gy in body (V5Gy) for CK and RA plans are 365.75cc and 291.01cc respectively. Least difference was observed in Dose Spillage Index (DSI75, DSI50, DSI25) among the compared plans.

Conclusion: The dosimetric differences between the two techniques wereminimal, hence the choice of techniquehad to focus on the delivery accuracy.

   P-11: Dosimetric Comparison of Dose to Water and Dose to Medium Prescription in Monte Carlo Algorithm for Lung, Pelvis and Head and Neck Cases Top

V. Ramya, Daicy George, P. Suresh Babu, S. Sowmya Narayanan

Department of Radiation Physics, Vydehi Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, India. E-mail: [email protected]

Introduction: Conventional Algorithms for photon beam dose calculations report absorbed dose to water (Dw) which is energy absorbed in small cavity of water divided by the mass of that cavity. Instead of treating human body as water of various densities, Monte Carlo (MC) dose calculation engine calculates dose to medium (Dm). Dm is energy absorbed in small cavity of tissue divided by the mass of the tissue element. There are arguments to support both the Dw and Dm. Doses reported in clinical trials are based on Dw and hence therapeutic ratio and Normal Tissue Tolerance are based on Dw. Hence Dw to be followed. To support Dm, it is said that, it is the quantity inherently computed by MC algorithm.

Objectives: When the calculation method changes, the absorbed dose of the given tissue changes and any difference between Dw and Dm leads to change of dose prescription. Hence in planning one has to decide whether to prescribe Dw or Dm. So far comparative study for Dw and Dm using commercially available MC is not conducted for various sites. There are methods available to convert Dw and Dm. If the dosimetric difference between Dw and Dm is known, the significance of conversion can be found. This study compares the Dosimetric quantities such as Planning Target Volume (PTV) maximum dose (Dmax), PTV minimum dose (Dmin), coverage (D95), Organ At Risk Maximum doses (OARmax) between the prescription methods of Dw and Dm for Head and Neck (HN), lung and pelvic cases using MC algorithm for photon beam calculation.

Materials and Methods: The study includes 5 HN, 5 cervix and 5 lung cases. Monaco (v 5.11.01) Treatment Planning System which is capable of doing biological optimization using X-ray Voxel Monte Carlo (XVMC) was used for planning. Calculation voxel size used was 3 mm. Lung cases were planned for Intensity Modulated Radiation Therapy (IMRT). Cervix and HN cases were planned using Volume Modulated Arc Therapy (VMAT). The initial plan was done using dose to medium (Dm) prescription. Keeping the optimization and other calculation properties same, the prescription changed to dose to water (Dw) and the plan was recalculated.

Results and Discussion: The difference between Dw and Dm was calculated using Dw − Dm × 100. We found that for the entire lung, cervix and Head and Neck cases Dw estimates more dose than Dm for Dmax of PTV and OARmax doses. For Lung cases the Dmax of PTV differs by 2.3 ± 1.4%, for carcinoma cervix cases 2.8 ± 1.9% and for HN cases 3.6 ± 1.3%. Spinal Cord in Lung cases differs by 2.8 ± 1.4% and Spinal Cord in HN cases differs by 2.2 ± 0.6%. The PTV mean, D95, OAR mean doses differs by less than a percentage in all the cases. And in carcinoma cervix the Maximum dose of head of femur differs by 4.0 ± 1.1%. Spinal Cord receives more dose in Dw prescription due to the fact that higher density bone causes higher fluence of secondary electrons when cells are infiltrated in bony tissue. It was found that for the bony structures and Spinal Cord, Dmax was more in Dw prescription and it was also found that PTVmax dose was higher in Dw prescription. Mean dose of PTV and OAR differences were negligible. OAR differences were negligible asshown in [Figure 1]. While using sophisticated algorithm such as MC, it is desired to evaluate the plans using Dm parameter, as Dm yields better dose volume predictor than Dw.
Figure 1: DVH comparison of Dw and Dm for carcinoma lung

Click here to view

   P-12: Design and Development of In-House Multichannel Applicator for HDR Vaginal Brachytherapy and Dosimetric Comparision with Single Channel Applicator Top

G. Kesavan, S. Senthilkumar1

Department of Radiotherapy, Vadamalayan Hospitals Pvt. Ltd., 1Department of Radiotherapy, Madurai Medical College, Govt. Rajaji Hospital, Madurai, Tamil Nadu, India. E-mail: [email protected]

Introduction: Endometrial cancer is one of the most common gynecologic malignancy. Vaginal cuff brachytherapy is a standard treatment option for postoperative endometrial and selective postoperative cervical cancer cases for women at high risk for vaginal recurrence. Single-channel vaginal cylinders are frequently used to treat the vaginal cuff, but they are limited in their ability to sculpt dose away from organs at risk (OARs). Multichannel applicators, through modulation of dwell times in various positions along the channels, improve the ability to optimize target coverage and to minimize dose to OARs. Despite evidence showing that the multichannel applicators significantly reduce dose to OARs compared with single-channel applicators. The ideal configuration of the multichannel applicator (shape, location and number of channels) is unknown. There are various multichannel applicator designs currently used in clinical practice.

Objectives: The main objective of this study was to design and development of a in-house multichannel applicator for HDR vaginal brachytherapy and dosimetric compression with the single channel applicator.

Materials and Methods: The multichannel applicator with a 3 cm diameter solid cylinder made up of PMMA. One channel in the centre of the applicator and eight are in the peripheral, which is 0.5 cm from the surface. The peripheral source channels of the multichannel cylinder are placed close to the treatment volume, which means that the dose gradient in the radial direction is steep. Therefore the dose is enhanced close to the cylinder surface and lowered at larger distances as compared to the central channel cylinder. We randomly selected 5 patients with endometrial carcinoma were CT-scanned twice with a vaginal cylinder single and multichannel applicator. CT-based 3D dose-planning was done for both applicator. The dose calculation algorithm is based on the TG-43 formalism, as recommended by the American Association of Physicists in Medicine (AAPM). Dose–volume histograms were compared for both target and organs at risk.

Results and Discussion: The Multichannel applicator design improves the dosimetry over single channel applicators. Results showed that a uniform dose around the dome of a cylinder as compared to single channel. In addition a more uniform dose distribution can be attained. Vaginal HDR brachytherapy using a multichannel vaginal applicator and inverse planning provides dosimetric advantages over single channel cylinder, by reducing the dose to organs at risk without compromising the target volume coverage, but at the expense of an increased vaginal mucosa dose.

   P-13: Study the Effect of Pelvic Heterogeneities on Rectum Dose Measurements Inside an Indigenously Make Female Pelvic Phantom and Rando Female Pelvic Phantom Using Mosfet Dosimeters Top

Deepak shrotriya, R. S. Yadav1

Department of Radiation Oncology, J.K. Cancer Institute, G.S.V.M. Medical College, 1Department of Physics, DAVPG College, Kanpur, Uttar Pradesh, India. E-mail: [email protected]

Introduction: Human body consists of variety of heterogeneous tissues and pelvis is the most heterogeneous regions. Pelvis has various tissues and materials like bones, soft tissues, fat, air cavities, faecal matter, urine, sometimes artificial prosthesis etc. For the successful radiotherapy treatment of female pelvic cancers, there is a need to study the effect of tissue heterogeneities on dose distribution inside the tumor and adjacent normal tissues.

Objective: The direct use of, in water dosimetric data, in the treatment planning of female pelvic cancer patients gives erroneous results. The aim of this study is to direct measure the planned doses at different rectum points inside an indigenously make female pelvic phantom and Rando female pelvic phantom using in-vivo dosimeters.

Materials and Methods: TN502RD mobile MOSFETs (Best Medical Canada) of standard sensitivity along with the reader module TNRD70W dose verification system is used for direct dose measurements at different rectal points inside both female pelvic phantoms, assuming that rectum is empty. Both phantoms are scanned using SOMATOM Emotion 16-Slice CT-Simulator (Siemens make) in 5 mm thick slices and CT-slices are transferred to Oncentra 3D-TPS in DICOMRT format. Doses are calculated by the TPS and the results are compared to in-vivo dose values measured with MOSFET dosimetric system at same rectal points.

Results and Discussion: Dose calculation algorithm in the TPS is designed such that the rectum is filled with water equivalent material but this assumption is not correct. The rectum is a hollow pipe filled with air and faecal matter and surrounded with other heterogeneous tissues, having different electron densities than water. In case of empty rectum, it is assumed that only air is filled in the rectum and results indicate that the dose measured in the both female pelvic phantoms by the MOSFETs' dosimetric system are in the range of 18-21% lower than the dose calculated by the TPS.

Conclusion: The treatment planning system has overestimated the rectum dose because it has not considered the pelvic tissue heterogeneities. Therefore, the direct dose measurements in female pelvic phantoms are useful for designing the HDR treatment plans before actual dose delivery.

   P-14: HDR Brachytherapy Source Calibration by Using Solid Phantom Top

M. Athiyaman, Hemalatha, Arun Chougule1, David, H. S. Kumar2

Departments of Radiological Physics and 2Radiotherapy, S.P. Medical College, AG Hospitals, Bikaner, 1Department of Radiological Physics, S.M.S Medical College, Jaipur, Rajasthan, India. E-mail: [email protected]

Introduction: The description “source calibration” refers to the estimation of the source strength expressed in one of the internationally recommended quantities either reference air kerma rate or air kerma strength. The modern Treatment planning systems dose calculation is performed by taking the Air kerma strength as the input. In routine practice the Air Kerma strength is measured in the Well type Ion chambers. However there are other methods such as In Air calibration method and calibration using solid phantoms. The use of In Air calibration method is limited to very few centers worldwide due to the involvement of complex parameters. In present scenario the source strength calibration is performed in solid phantoms along with well type Ion chambers.

Objective: Estimation of Airkerma strength by using solid phantoms and exploring the associated influencing parameters

Materials and Methods: The measurements were performed for miniature Co-60 source in HDR Brachytherapy machine (Make: Eckert and Ziegler GmbH Bebig, Model: Multisource, Sr. No: 542) for miniature Co-60 source. The cylindrical solid phantom made by PMMA material was used. In water calibrated Farmer type ionization chamber, 0.60 cm3 (PTW Freiburg, S. No: 007023) was used for ion collection. The clinically used Esophagus guide tube was used for positioning the source. The ion chamber is kept at the fixed distance of 8 cm from the guide tube inside the phantom. The maximum response position was found and the meter reading was obtained.

The air kerma strength is estimated as below mentioned

Sk = Nk M ku kτ kρ kt k p k ion kv kwall k appl k ph(A)

Sk – air kerma strength in cGy h-1 cm2, Nk - air kerma calibration factor of the chamber for the γ -energy of the radionuclide considered, usually expressed in Gy/C, M- measured charged collected during time interval, Along with routine influence factors such as temperature and pressure, ion recombination and polarity correction factors additional factors were considered namely gα, kph, kwall, μen/ρ (air to water) where, gα – energy fraction of the electrons liberated by photons in air, that is lost to radiative processes, kph – correction factor to account for the existence of the phantom material and hence, some absorption and scattering effects, when the material is compared to air, kwall – correction factor accounting for attenuation and scattering effects of the chamber wall, μen/ρ (air to water) - ratio of mass energy absorption coefficient of air to that of water.

Results: The Airkerma strength was estimated as per above mentioned formula A. The measured strength was compared with the TPS Airkerma strength. The deviation is 2% from the measured value and within the tolerance.

Discussion: The estimation of source strength through solid water phantom is simple procedure and it can be extended for many clinical Brachytherapy units. The values of influence parameters have to be added carefully to obtain accurate result.

   P-15: Dosimetric Effects of Step Size of Cobalt-60 HDR Source in Intra Luminal Brachytherapy Top

Pawan K. Jangid, Arvind Shukla, Narendra Rathore, Abhay Jain, Vikram S. Rajpurohit, Vaihav Gagrani

Department of Radiotherapy, RNT Medical College and Associated Hospitals, Udaipur, Rajasthan, India. E-mail: [email protected]

Introduction: The step size plays major role in optimization process where optimization is maximum acheiveable. The challenge is to select the optimal step size for the unique clinical situation of patient is to spare normal tissues and to best implementation of optimization technique. Most of brachytherapy systems use standard step size as 2.5 mm for treatment. The step size is the distance between two dwell positions. In the present work we have studied the role of step size in brachytherapy treatment planning as it is a very important parameter and to evaluate the optimum source step size for better treatment of cancer patients using a Co-60 source.

Objective: The objective of the present study is to analyze the effects of Step Size of cobalt-60 HDR source in esophagus cancer.

Materials and Methods: A Bebig Multisource® HDR Brachytherapy unit with cobalt-60 HDR miniature source (Eckert and Ziegler, Bebig, Germany) was used for study. The Co-60 source has an active core 0.5 mm diameter and 3.5 mm active core length. HDR 2.5 plus (Eckert and Ziegler, Bebig, Germany) Treatment planning system was used for the study. 10 patients of carcinoma esophagus were taken for the study of dose distribution around the single intraluminal catheter of 8 cm length. The effect of step size around the catheter was studied for depth doses were calculated at 0, 2.5, 5 mm and 10 mm from the applicator surface. Dose point based optimization and normalization were used to calculate the 4.0 Gy prescription dose at 5 mm depth. Dose distribution and homogeneity for the various source step sizes were evaluated by performing dose computations per step size and calculating the average dose and standard deviation at each depth.

Results and Discussion: The study shows that standard deviation between the doses reduces as depth increases. The average standard deviation was 0.92, 0.43, 0.27 and 0.14 for depth 0 mm, 2.5 mm, 5 mm and 10 mm respectively [Table 1]. Study in carcinoma Esophagus concludes that homogeneity increases as the step size reduces.
Table 1: Variation of standard deviation with step size in esophagus cancer

Click here to view

   P-16: A Reference Study of Detector Materials for Bnct-Spect Imaging: A Simulation Study Top

Moo-Sub Kim, Joo-Young Jung, Han-Back Shin, Sunmi Kim, HyeJeong Yang, Kazuki Kubo1, Kohei Shimomura1, Hajime Monzen1, Do-Kun Yoon, Tae Suk Suh

Department of Biomedical Engineering, Research Institute of Biomedical Engineering, College of Medicine, Catholic University of Korea, Seoul, Korea, 1Department of Medical Physics, Graduate School of Medical Science, Kindai University, Osaka, Japan. E-mail: [email protected], [email protected]

Purpose: To investigate the optimal detector material for prompt gamma ray imaging during boron neutron capture therapy (BNCT) with a Monte Carlo simulation.

Materials and Methods: Sixteen detector materials used for radiation detection were estimated to assess their advantages and drawbacks. The estimations used previous experimental data to build the simulation codes. The energy resolution and detection efficiency of each material was investigated.

Results: Prompt gamma ray images during BNCT simulation were acquired using only the detectors that showed good performance in our preliminary data. From the simulation, we could evaluate the majority of detector materials in BNCT as shown in [Figure 1]. We also could acquire a prompt gamma ray image using the six high ranked-detector materials and lutetium yttrium oxyorthosilicate as listed in [Table 1].
Figure 1: Trend of detection efficiency (left label, black square) and energy resolution (right label, blue triangle) according to the detector material. The best detector efficiency was observed when BiI3 was used as the detector material. Each detection efficiency value was normalized by using the detection efficiency of BiI3 as reference. Each energy resolution value at 478 keV prompt gamma ray peak was calculated from the energy spectrum of each detector material

Click here to view
Table 1: Units for list of the sixteen detector materials for prompt gamma ray imaging during boron neutron capture therapy

Click here to view

Conclusions: We provide a strategy to select a detector material for the prompt gamma ray imaging during BNCT.

   P-17: Data Driven Motion Correction of Spect Using Developed Algorithm 0with Partial Reconstruction Top

Md. Nahid Hossain, Kamila Afroj Quadir1, Adnan Kiber2, Roger Fulton3

National Institute of Nuclear Medicine and Allied Sciences, 1Bio-Science Division, Bangladesh Atomic Energy Commission, 2Department of Electrical and Electronic Engineering, University of Dhaka, Dhaka, Bangladesh, 3Department of Medical Physics, Westmead Hospital, Westmead, Australia. E-mail:

Introduction: In a Single Photon Emission Computed Tomography (SPECT) study, the data acquisition is performed over a relatively long time, typically in the range of 5-30 minutes. Patient movement frequently occurs for longer time of data acquisition in clinical procedure. This movement causes misalignment of the projection frames, which degrades the image quality. These motion artifacts may significantly affect the diagnostic accuracy. When motion occurs between discrete acquired projections, consistency is lost and errors are generated in the reconstructed estimate. Motion correction is the task of obtaining consistent projection data from the acquisition. Therefore, the motion correction of patients in tomography images is very much essential for accurate diagnosis and hence achieves the quality of the images.

Objectives: In this work, we corrected a SPECT study for a single movement during acquisition. Data driven motion correction was applied in the SPECT data using developed algorithm with partial reconstruction.

Materials and Methods: Different data without motion were acquired by using a Dual head SPECT camera and a Hoffman 3D brain phantom. The SPECT camera has two opposing heads, and acquires 64 views over 360 degrees. For that the camera makes 32 steps. We worked with 64 x 64 x 64 voxel reconstructions. We reconstructed the data with ordered subsets expectation maximization (OSEM) algorithm. This required to define the number of projections per subset. The natural choice of subsets for OSEM is therefore 1 subset = 1 pair of opposing views. First we created some simulated data. We created an arbitrary using algorithm transformation. We applied 6 degree of freedom parameters like (0, 0, 0) for translations and (15, 8, 0) for rotations to the data and created another data. There are two SPECT scans (simulated) with the phantom in two orientations. We could combine projections from both to create a simulated SPECT scan with a movement at the mid-scan point. We performed motion corrected reconstruction of the simulated SPECT scan in which 16 projections were acquired prior to the motion, and 16 were acquired after the motion. The motion was treated as instantaneously occurring between projections 16 and 17. Any other timing of the motion could be simulated in the same way. The next step was to perform motion correction. First we reconstructed from the first 16 pairs, to obtain a partial reconstruction. Then we reconstructed simulated data from the second 16 pairs. When we applied the invert transformation with the data, we achieved the final motion corrected data. The all algorithms were developed with Interactive Data Language (IDL) program.

Results: The six degree of freedom (dof) motion parameters were converted to a transformation matrix using the developed algorithm. A 4x4 transformation matrix was produced. This transformation was applied to the reconstructed data. After correcting motion the reconstructed image was shown with motion free. But when we compared the corrected final data with the motion free data, we observed that corrected final was more blurred. This was due to interpolation effects when applying the transformations.

Discussion: Motion detection techniques are classified into two categories, external based or internal based. The data driven method was included in internal based technique. The field of motion detection and correction in SPECT is very open to future novel ideas especially software based improvement of motion estimation, characterization and compensation. The simulated data is very essential for examining the algorithm base methods.

   P-18: Practical Aspect of Design of Optical Stimulation Assembly for Multisample TL-OSL Reader System Top

L. Paliwal1, M. Uke1, M. S. Kulkarni2, D. Dutta1

1Radiological Physics Advisory Division, Bhabha Atomic Research Centre, 2Radiation Safety System Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: The thermoluminescence (TL) and optically stimulated luminescence (OSL) reader systems are in great demand in all the research institutes and universities for their manifold applications in radiation dosimetry and luminescence dating. The advance integrated TL-OSL reader systems commercially available are not only expensive but the maintenance of such systems is also difficult and expensive. Therefore, indigenous development of TL-OSL reader system has a great scope for further expansion in India for environmental monitoring, medical and retrospective radiation dosimetry. The development of a multiple sample TL-OSL reader system as shown in [Figure 1] was undertaken by us which is low cost but equally competent having facility for readout of eight samples in sequence in a programmed way. This paper reports the practical aspect of design of a new Multisample TL-OSL Reader System which works either in TL, OSL or simultaneous TL-OSL modes of operation.
Figure 1: Multisample TL-OSL Reader System

Click here to view

Materials and Methods: The optical stimulation (photo excitation) of the samples is carried out by power LED clusters (Blue LXHL-NB98 and IR HSDL 4230). High power Blue LEDs that yields an output of 1.0 W at λp ≈ 470 nm and Δλ ≈ 20 nm. A long pass filter (GG-435) is incorporated in front of each blue LED cluster to minimise the amount of directly scattered blue light reaching the detector system. Optical stimulation assembly consists of two blue LEDs placed in two channels facing each other at an angle of 30° with the vertical axis with 20 IR LED arranged in circular fashion as shown in [Figure 1]. The user can select the blue or IR light stimulation depending on the OSL samples under study and the current is passed through the selected LEDs only. During the stimulation cold nitrogen gas is flushed continuously on it at a flow rate of ≈ 3 LPM to ensure that the junction temperature remains well within the tolerance limit.

In principle, If the sample is heated or illuminated on a metal support, the maximum light signal is then reduced to about 50% (to 2πr geometry). To reduce sample-to-PM tube distance sample is lifted through slots in indexing disc into the measurement position by a lift, which also functions as heating element. In the measurement position the sample can be stimulated thermally and/or optically. The emitted luminescence is measured by the light detection system.

DC motor has been used to lift the sample mounted on indexing disc for measurement and also for heating. As the stimulating light beam is focused on the sample in the lifted condition, design care has been taken to achieve repeatability within ± 0.01 mm at the lifted extreme end. Another DC motor has been used to move the photodiode plate to measure the stimulating light on sample. Four Proximity sensors (Flush type) have been provided to get the feedback on extreme positions.

Results and Discussion: In reader S1133-14 photodiode has been used to determine the stimulation light intensity at the sample position for the given wavelength. Photosensitivity of photodiode is .22 A/W for Blue LED (435 nm) and .37 A/W for IR LED (875 nm). The light intensity at the sample position varied in the range of 0.02 mW/cm2 to 100 mW/cm2 (percentage standard deviation of ±5%) by controlling the DC current through the LED cluster as shown in [Figure 2]. The light intensity is measured to be 100 mW/cm2 through the blue LED cluster and 67 mw/cm2 for 600 mA through IR LEDs.
Figure 2: Blue LED response with photodiode and IR LED response with photodiode

Click here to view

   P-19: Development of In-Line Holographic Phase-Contrast Imaging System Using Industrial X-Ray System Top

Daisuke Shimao, Erika Nakajima1, Hitoshi Sato

Department of Radiological Technology, Faculty of Health Sciences, Hokkaido University of Science, Sapporo, 1Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, Inashiki, Japan. E-mail: [email protected]

Introduction: X-ray imaging has been widespread diagnostic tool in medicine which is based on X-ray absorption. Its image contrast is sufficient for boundaries between tissues with greatly different absorption coefficient, but little or no image contrast appears with almost the same absorption coefficient. Over the past 20 years, alternative imaging techniques based on X-ray refraction (phase shift) have been intensively explored and developed to overcome weak image contrast in soft tissue imaging by existing method based on X-ray absorption. Such alternative imaging techniques include in-line holographic phase-contrast imaging, angle-analyzer-based imaging, and crystal interferometry. All of these techniques can produce fine images of soft tissues when using synchrotron X-rays which provide both monochromatic X-ray with sufficient intensity and high directivity. Necessity of synchrotron faculty for these alternative imaging techniques, however, is an obstacle for these techniques to be used in medicine.

Objectives: To develop in-line holographic phase-contrast imaging system needing no synchrotron X-rays, but based on the industrial X-ray tube.

Materials and Methods: We utilized X-ray generator with fixed anode X-ray tube (ISOVOLT Titan E; GE Measurement & Control Solutions) that has a generating capacity of 3 kilowatts. The target material was molybdenum and the focus size was 1 mm by 5 mm. Characteristic X-rays of molybdenum (17.4 keV and 19.6 keV) were extracted by a monochromator made by perfect silicon crystal. The monochromator produced vertically long X-ray beam of 17.4 keV and 19.6 keV at Bragg reflection condition, which appeared side by side with each other at the distance of around 1 m from the monochromator. Because of vertically long X-ray beams, we performed line scan technique to acquire two dimensional images of objects. We utilized imaging plate or X-ray CCD camera as image detector and adopted X-ray chart or breast cancer specimen as the imaging objects. The distance between objects and image detector was set at approximately 1 m.

Results and Discussion: Clear edge enhancement could be acquired on both X-ray chart and breast cancer specimen. The edge enhancement appeared only in the horizontal direction. This is because plane of incidence for the monochromator was horizontal plane and then divergence angle of reflecting X-ray beam from monochromator was collimated only horizontal direction. On the other hand, reflecting X-ray beam from monochromator in vertical direction diverged naturally and then X-ray images were enlarged in the vertical direction. Although exposure times were considerably prolonged due to weak X-ray intensity compared to synchrotron radiation, we could acquire phase-contrast images in in-line holographic method using industrial X-ray system.

   P-20: Four-Dimensional Digital Tomosynthesis Based on Visual Respiratory Guidance Top

Dong-Su Kim1, Seungwan Lee2, Siyong Kim3, Tae-Ho Kim1, Seong-Hee Kang1,4, Kyeong-Hyeon Kim1, Dong-Seok Shin1, Hye Jeong Yang1, Tae Suk Suh1

1Department of Biomedical Engineering, Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, 4Department of Radiation Oncology, Seoul National University Hospital, Seoul, 2Department of Radiological Science, College of Medical Science, Konyang University, Daejeon, Korea, 3Department of Radiation Oncology, Virginia Commonwealth University, VA, USA. E-mail: [email protected]

Introduction: Patient breathing-related sorting method of projections in 4D digital tomosythesis (DTS) can be suffered from severe artifacts due to non-uniform angle distribution of projectionsand noncoplanar reconstructed images for each phase. In this study, we propose a method for optimally acquiring projection images in 4D DTS.

Materials and Methods: In this method every pair of projections at x-ray tube's gantry angles symmetrical with respect to the center of the range of gantry rotation is obtained at the same respiration amplitude. This process is challenging but becomes feasible with visual-biofeedback using a patient specific respiration guide wave which is in sinusoidal shape (i.e., smooth and symmetrical enough). Depending on scan parameters such as the number of acquisition points per cycle, total scan angle and projections per acquisition amplitude, acquisition sequence is pre-determined. A simulation study for feasibility test was performed. To mimic actual situation closely, a group of volunteers were recruited and breathing data were acquired both with/without biofeedback. Then, x-ray projections for a humanoid phantom were virtually performed following (1) the breathing data from volunteers without guide, (2) the breathing data with guide and (3) the planned breathing data (i.e., ideal situation). Images from all of 3 scenarios were compared.

Results: Scenario #2 showed significant artifact reduction compared to #1 while did minimal increase from the ideal situation (i.e., scenario #3). Also, the scan angle dependence-related differences in the DTS images could reduce between using the proposed method and the established patient breathing-related sorting method.

Conclusion: Through the proposed 4D DTS method, it is possible to improve the accuracy of image guidance between intra/inter fractions with relatively low imaging dose.

   P-21: An In-Vitro Study to Diagnose and Distinguish Breast and Lung Cancers Using the PCB Technology Based Nanodosimeter Top

P. Venkatraman, C. S. Sureka

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: In the modern field of nanodosimetry, the Printed Circuit Board (PCB) technology based positive ion detector has been identified as a device to detect cancers in lungs and breast region. In the nano environment, these cancer cells have been diagnosed by the exhalation of specific volatile organic compounds (VOCs) which serves as eminent source biomarkers for cancer diagnosis. Earlier studies reported that lungs emit various VOCs include Benzene, Ethylbenzene, Cyclohexane, methanol, ethanol, dodecane and tridecane, and the Ca. breast emit alkanes, alkenes, ketones, halogenated hydrocarbons, aldehydes, alcohols, esters, unsaturated hydrocarbons, terpenes, siloxanes, and aromates. By employing VOCs exhalation, the field of nanodosimetry aids as a direct evidence that the diagnosis of critical organs like lungs and breast cancer cells without harming the patients is possible.

Objective: The objective of the present work is to diagnose lung and breast cancers and distinguish them using the PCB technology based Nanodosimeter.

Materials and Methods: The normal lung and breast tissues were placed separately inside the chamber and it was evacuated in order to remove all other molecules present in the chamber. Then, it is allowed to exhale molecules at various pressures in order to measure the amplitude, rise time, fall time, and number of pulses of the signal. Later, these normal tissues were replaced by cancerous tissues of stage 4 in the evacuated medium and the same was allowed to exhale Volatile Organic Compounds (VOCs) to capture signal at various pressures ranging from 1 to 10 Torr. This procedure was repeated for 3 sets of both normal and cancerous tissues of breast and lung at stage 4 to assure reliability.

Results and Discussion: It is observed that the signal amplitude, rise time, fall time and number of pulses of normal lung and breast tissues was found to be 72.9±0.02 Volts, 2.4±0.005 ms, 480±0.0 μs, 781±72 and 74.1±0.08 Volts, 2.4±0.005 ms, 480±0.0 μs, 581±40.5 respectively. Similarly, the signal amplitude, rise time, fall time and number of pulses at stage 4 of lung cancer tissues was found to be 86.3±0.06 Volts, 1.3±0.01 ms, 430 ±0.012 μs and 3008±231.125 and for breast tissues: 91.5±0.03 Volts, 470±0.2 μs, 480±0.0 μs, and 4077±210.12. From this data, it is found that the signal amplitude, rise rime, fall time and number of pulses are higher for breast cancer tissues than lung tissues. This is due to the higher rate of emission of VOCs from breast cancer tissues than the lung cancer tissues. Based on these, it is concluded that the PCB technology based 3D positive ion detector can be developed to diagnose and distinguish breast and lung cancers.

   P-22: Indigenous Preparation and Study of Radiochromic Film as Radiation Dosimeter for Medical Applications: A Preliminary Work Top

Apoorva Mittal, Rahul Sharma1, ParveenSaini1, R. K. Kotnala1, Pratik Kumar

Medical Physics Unit, Dr. B.R.A. IRCH, All India Institute of Medical Science, 2Environmental Sciences and Biomedical Metrology Division, CSIR-National Physical Laboratory, New Delhi, India. E-mail: [email protected]

Introduction: In medical field, radiation dosimetry is concerned with quantifying the energy deposited in terms of absorbed radiation dose. Ionizing radiations are widely used in medical procedures such as computed tomography, fluoroscopy, x-ray radiography, mammography etc. which help the doctors in better diagnosis and treatment. However, radiation exposure in any amount entails potential risk which increases with the radiation dose. It is extremely important to accurately determine and optimize the amount of radiation dose to which a patient is exposed during any radiological procedure. Radiochromic films are used for the measurement of radiation dose. These films change color directly upon exposure to radiations. They have high spatial resolution. However, commercially available radiochromic films, for which there is currently a sole manufacturer, are very expensive which limits their regular use in radiation dosimetry. Also, they have major limitations like post-irradiation instability, temperature dependence and ambient light sensitivity. The sensitive layer of presently available films has a preferred direction for irradiation and literature reports that scanning in different direction produces anomalous results. It is extremely important to minimize the effect of various factors like temperature, humidity, pressure etc. on the stability of these films. All these limitations restrain their ease of handling and stability. This creates the necessity for indigenous development of radiochromic films having distinguished advantages in terms of performance, cost and availability.

Objectives: Development of low cost radiochromic films with improved characteristics in terms of sensitivity and handleability.

Materials and Methods: Herein, we have prepared monomeric ingredients based polymeric radiochromic films by simple and cost effective solvent casting method. These monomeric species in the films undergo radiation induced polymerization involving cross-linking of polymers which is eventually responsible for change in optical properties particularly the color and its intensity.

Results: The prepared films are bubble-free, flexible and sturdy. The optical characterization of these films showed a change in optical density before and after the exposure.

Discussion: This work offers a cost-effective way of fabricating indigenous radiochromic films via a facile route which may be easily scaled up for commercial development of radiochromic films. These films may also be used as radiation dosimeter in the food industry, agricultural and other strategic sectors. The self-indicating nature of radiochromic films can also be used as immediate responders in case of any nuclear accident or for early detection of radiation leakage from other sources.

   P-23: Dosimetric Effects of Brass Mesh Bolus on Skin Dose and Dose at Depth for Postmastectomy Chest Wall Irradiation Top

Zakiya S. Al-Rahbi1,2, Dean L. Cutajar1,3, Peter Metcalfe1, Anatoly B. Rosenfeld1

1Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 3St. George Cancer Care Centre, St. George Hospital, Kogarah, Australia, 2Department of Radiotherapy, National Oncology Center, The Royal Hospital, Muscat, Oman. E-mail: [email protected]

Purpose: To investigate the feasibility of using the Brass Mesh Bolus as an alternative to tissue-equivalent Bolus for post mastectomy chest wall cancer by characterizing the dosimetric effects of the 2-mm fine Brass Bolus on both the skin dose and the dose at depth.

Materials and Methods: Surface dose and percent depth dose data were acquired for a 6 MV photon beam in a solid water phantom using MOSkin TM dosimeter, Gafchromic EBT3 film and an Advanced Markus ionization chamber. Data were acquired for the case of: no bolus, Face-up Brass Bolus, Face-down Brass Bolus, Double Brass Bolus, 0.5 cm and 1.0 cm of Superflab TE bolus. The exit doses were also measured via MOSkin TM dosimeter and Markus ionization chamber.

A tangent chest wall field was delivered to the curved phantom with no bolus, brass mesh bolus, and Superflab bolus, and Gafchromic EBT3 film was used to measure surface dose over the irradiated area.

Results: The surface dose measured under the Bolus by Markus ionization chamber increased from 17.1% without bolus to 55.5%, 54.2% 72.9%, 90.1% and 102.2% (± 0 SD) with Face-up Brass Bolus, Face-down Brass Bolus, Double Brass Bolus, 0.5 cm and 1.0 cm TE-Bolus, respectively, whereas, the surface dose measured under the Bolus via MOSkin TM dosimeter increased from 19.2 ± 1.0% without bolus to 63.0 ± 2.1% and 61.5 ± 0.5% for Face-up Brass Bolus and Face-down Brass Bolus, respectively. The surface dose measured by Gafchromic EBT3 film showed that the surface dose increased from 24.0 ± 1.0% to 58.6 ± 1.1% with only one layer of Brass Bolus and 71.0 ± 1.0% with double layer of Brass Bolus.

The measured exit doses increased from 53.8% without Bolus to 78.8%, 79.4%, 86.3%, 63.5% and 64.3% for the cases of Face-up Brass Bolus, Face-down Brass Bolus, Double Brass Bolus, 0.5 cm and 1.0 cm Superflab TE-bolus measured by Markus ionization chamber, where the exit doses measured by MOSkin TM increased from 47.9 ± 0.5% without Bolus to 74.1 ± 0.4% for Face-up Brass Bolus and 77.5 ± 0.1% for Face-down Brass Bolus.

The Markus ionization chamber measurements show that the doses at depth 100 mm is nearly the same for brass mesh bolus versus no brass bolus, where the percent difference is less than 0.5% with Brass Bolus versus without Brass Bolus, whereas the doses decrease by approximately 1.0% for TE-bolus.

For the tangent field measured in the curved phantom with Gafchromic EBT3 film, the surface dose ranged from 23.5% - 59.9% of the delivered dose in case of no Brass Bolus. The surface dose is increased to 62.0% - 89.9%, 63.5 – 92.2%, and 75.4 – 94.3% of prescription dose for the Face-up Brass Bolus, Face-down Brass Bolus and Double Brass Bolus, respectively. The TE Bolus increase the surface dose more than the Brass bolus. The surface dose increased to 94.9% and 107.5% of prescription dose for the 0.5 cm TE Bolus and 1.0 cm Superflab TE Bolus respectively.

Conclusions: Brass Mesh Bolus does not significantly change dose at depth (less than 0.5%), and the surface dose is increased similar to TE bolus. Considering this, brass mesh may be used as a substitute for TE bolus to increase superficial dose for chest wall tangent plans.

   P-24: Peripheral Photoneutron Dose Measurement in Medical Linear Accelerator Using BD-PND Bubble Detector Top

K. Hajee Reyaz Ali Sahib1,2, Bharanidharan1, Nandakumar1, Ben Johnson<3, D. K. Mohapatra2, Prakasarao Aruna1, Thilagam2, Kathiresan3, Muthuvel Murgan3, Singaravelu Ganesan1

1Department of Medical Physics, Anna University, 2Nuclear Safety Analysis Section, Safety Research Institute, Atomic Energy Regulatory Board, Kalpakkam, Chennai, Tamil Nadu, 3Department of Radiation Oncology, VPS Lakeshore Hospital, Kochi, Kerala, India. E-mail: [email protected]

Introduction: Cancer is the one of the greatest threat and leading death worldwide. Megavoltage photon beams operating above threshold energy of 10 MV produce photoneutron contamination by (γ, n) reaction. These photoneutron gives additional dose to patients and increase the integral dose. Hence, determination of photoneutron dose in a LINAC is current research interest.

Objective: The present study analyze and estimates the effective peripheral photo-neutron dose along the patient plane produced in linear accelerator (Elekta Versa HD) for 10 MV (FF and FFF) and 15 MV photon beams using BD-PND bubble detector.

Materials and Methods: The BD-PND bubble detector has flat dose response for range 200 KeV to 15 MeV. The BD-PND bubble detector used in our study has sensitivity 1.1 bubble/μSv. In air out-of-field neutron dose were measured by placing the BD-PND bubble detectors on horizontal plane at source to detector distance (SSD) of 100 cm. For the measurement the gantry angle and collimator angle were fixed at 0o and the dose of 200 MU was delivered at a dose rate of 550 MU/Min for 10 MV (FF), 2180MU/Min for 10 MV (FFF) and 635 MU/Min for15 MV (FF). Photoneutron doses equivalent (μSv/MU) were measured by placing BD-PND detectors along axis on the patient plane i.e. (Longitudinal In and Out, Lateral Left and Right) at 10 cm, 20 cm and 30 cm away from standard reference field size of 10x10 cm2.

Results and Discussion: From the analysis; outside the primary beam no photoneutron dose was observed for6 MV (FF & FFF) photon beam along the patient plane. Where as a photoneutron dose was observed in 10 MV (FF & FFF) and 15 MV photon energies. For equivalent distance from the primary beam on each side, it has been observed that there is a negligible variation of photoneutron dose. It has also been observed that the dose is inversely proportional to the distance. Comparing 10 MV (FF) with 10 MV (FFF), latter accounts less photoneutron dose due to absence of Flattening Filter, whereas 15 MV (FF) exhibits higher photoneutron dose compared with 10 MV (FF) by a factor of 2.5 to 2.8 in all peripheral distances.

Conclusion: From our study, we can conclude that for clinical usage of photon energies above 6 MV the contamination of scattered photoneutron field increases. The maximum allowed neutron leakage percentage in patient plane is much less than permissible limits govern by regulatory board requirements. It is also concluded that BD-PND bubble detector is reliable, accurate, high sensitivity in neutron dosimetry for photoneutron dose measurement in accelerator because of it is unique attractive features such as instant dose calculation, Isotropic nature, less weight, compactable size, no moderator and flat dose response for wide neutron energy. However the BD-PND bubble detectors have limited life time, the recovery time of 3 hours between two consecutive readings, the sensitivity in dose prediction varies (±10%) for the same point in the same conditions on frequent usage, improper storage and ageing factors affect the temperature compensation resulting in the increase of the sensitivity at elevated temperatures, the detector also becomes sensitive to gamma radiation.

   P-25: Investigation of Reconstructed Filters of Optical Computed Tomography for Polymer Gel Dosimeter Top

H. Kawamura, T. Takanashi1, Y. Sato, Y. Shimada, S. Abe

Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, Inashiki, 1Innovation Center, 3D Gel Dosimeter Research Laboratory, RIKEN, Wako, Japan. E-mail: [email protected]

Polymer gel dosimetry, which utilizes chain polymerization that is proportional to radiation dose, is a new three-dimensional dosimetric tool for quality assurance. It could potentially be used to measure 3D doses in clinical radiotherapy. Dose evaluation method for polymer gels was selected R2 method using MRI for dose linearity and image quality.

In this study, we construct optical computed tomography (OCT) system for evaluation of polymer gel dosimeter. Some advantages of the dose evaluation using OCT are low cost, bench top, capability of reading dose distribution with high spatial resolution and low noise. The original OCT was composed of He-Ne laser for light source, photodiode for detector, rotation and linear motion stage, controller for stage operation. Projection data per angle were acquired from turned gel samples using mechanical stages for moving and turning. Acquired transmission data per angles was reconstructed with Filtered Back-Projection (FBP) method. Irradiated PAGAT polymer gel samples were prepared. The gel samples were irradiated to 2, 4, 6, 8 Gy respectively, with X-ray beams. The non-irradiated and irradiated samples were scanned using the OCT. The mean optical density from reconstructed images using OCT data was measured. The dose-response curves of the ROI measurements from different pre-reconstructed image filters, Hann filter, Butterworth filter, Ramp filter were compared.

The results of the optical density from irradiated gel samples were tends to raise with increasing dose. The dose responses using three filters were not linear. The dose response curve from reconstructed images using Hann filter could be adapted polynomial curve (correlation coefficients: r2=0.994). The dose response curve using Hann filter was shown excellent result from correlation coefficients.

   P-26: Evaluation of Displacements for Set Up Reproducibility in Left Sided Breast Cancers with Portal Imaging and Digitally Reconstructed Radiographs Top

Deboleena Mukherjee, Sachin Taneja, Kirti Tyagi, Arti Sarin1

Radiation Oncology Centre, INHS Asvini, 1Nuclear Medicine Department, INHS Asvini, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Breast cancer is the most frequently diagnosed cancer among women in 140 of 184 countries worldwide. Studies of setup reproducibility in radiotherapy (RT) for breast cancer have largely focused on breast tangential treatments alone. Inaccuracies in treatment set up reproducibility may increase toxicities to organs at risks (OARs) (heart and lung) especially in left sided breast cancers. Studies have shown that the central lung distance (CLD) measured by an electronic portal images (EPIs) are due to displacements in three directions namely, anterior-posterior (AP), superior-inferior (SI), and medial-lateral (ML) for the three dimensional (3D) treatment plan with treatment planning system (TPS). In this paper we will discuss the evaluation of displacements in these three directions with EPIs and digitally reconstructed radiographs (DRRs) of left sided breast patients.

Materials and Methods: This study was carried out on approximately 50 patients (left sided), breast conserving surgery (3/50) and mastectomy (47/50) between ages 25-75 yrs (median age 50 yrs) treated with external beam radiation therapy (EBRT) during a period of 24 months at INHS Asvini. Patients were clinically marked for breast/chest wall field borders with fiducial radio opaque markers and then immobilized on a commercially available inclined Breast board in treatment position for whole breast scan (virtual simulation) by 16 slice CT scanner (Siemens). Three markers were placed at the central axis of the treatment field. Two straight lines meeting the SI and ML field borders and joining the central marker was drawn and four reference markers were placed, one each at the midline of this SI and ML field borders and distances from upper, lower and lateral borders with this central marker were noted. These DICOM CT images were imported to TPS OncentraTM (Elekta) for contouring OARs and Planning Target Volume (PTV) on each CT slice for all these patients. A 3D treatment plan with 6MV photons (Linear Accelerator, Siemens) for a prescribed dose of 50 Gy in 25 fractions at isocentre with two coplanar conventional tangential fields at two gantry angles as per International guidelines was generated. Mean doses to OARs and linear measurements for set up SSD (distance of the perpendicular drawn from isocentre to the upper skin border (AP) distance) and CLD on isocentric slice was calculated for each case on the 3D reference approved plan and was exported to Primeview workstation (Siemens) for EPIs for both tangential fields. Reference DRR and EPIs obtained on first day and weekly thereafter was superimposed to verify deviations in all the three directions for all patients.

Results: In the analysis of magnitude and directions of all displacements of the EPIs compared with the DRRs (n=141) for the supraclavicular nodal Anterior field of 47 chest wall irradiation patients, 75% were ≤5 mm, 11% were >5 mm and ≤7 mm, 9% were >7 mm and <10 mm, and 5% were ≥10 mm in the all three directions, and for tangential breast/chest wall fields of all 300 EPIs with DRRs of all 50 patients, 87% were ≤5 mm, 3% were >5 mm and ≤7 mm, 7% were >7 mm and <10 mm, and 3% were ≥10 mm in the AP direction, the corresponding values in ML direction were 92%, 6%, 1%, and 1% and in the SI direction, the corresponding values were 90%, 5%, 3% and 2%, respectively. The shifts observed in CLD was more for obese patients with set up SSD > than 4.5 cm due to difficulty in maintaining the arm position on breast board and motion of heart due to respiration.

Conclusion: Using portal imaging and DRRs, the treatment set up reproducibility of patient position is improved significantly in left sided breast cancer.

   P-27: Effect of Contrast Agents on Spatial Dose Distribution Using Different Calculation Algorithms Top

M. Kang1,2, B. Park2, Y. Bae2,3, J. Lee2,3

1Department of Medical Physics, Korea University, 2Department of Radiation Oncology, Konkuk University Medical Center, 3Department of Convergent Medical Physics, Konkuk University, Seoul, Korea. E-mail: [email protected]

Introduction: Intravenous (IV) contrast agents have been used widely in planning CT since contrast agents can improve the visualization of normal organs and malignant tissue in CT scans. However, there is concern that high atomic number of a contrast agent (CA) may cause errors in the dose calculation in radiation planning process. Dose discrepancy due to CA could affect monitor unit (MU) calculation as well as spatial dose distribution. It could be more critical issues in intensity-modulated radiation therapy (IMRT) using non-uniform small beamlet than in conventional uniform beam treatment. Therefore, it is necessary to investigate the effect of CA on spatial dose distribution and dose calculation in IMRT. In this study, we investigate and quantify the effect of CA on dose distribution using home-made phantom. In addition, the dependency of dose calculation algorithms on the effect of CA was also evaluated with IMRT plans.

Materials and Methods: The phantom was designed with the square size of 40×40 cm2 plastic material with 20×20 cm2 central hole filled with paraffin. The cylindrical CA container (diameter of 3 cm, thickness of 5 cm) was placed in the center of the phantom to simulate an enhanced tissue with CA. The CA was mixed with sodium chloride saline and diluted to be approximately 500 Hounsfield Unit (HU). We made two volumetric modulated arc therapy (VMAT) plans with/without CA to evaluate the effect of CA on spatial dose distribution. Once a treatment plan was generated based on anisotropic analytical algorithm (AAA) in the treatment planning system (Eclipse, v.13.6, Varian, Palo Alto, USA), it was recalculated using the Acuros® XB (AXB) to compare the dependency of dose calculation algorithms. The volumetric dose data was analyzed with the Vn% (defined by volume receiving n% dose). The dose was segmented with a contoured structure to determine the dose-volume. To quantitatively analyze spatial dose distribution, we used gamma index in commercial dose analysis software (OmniPro IMRT v.1.7, IBA, Germany).

Results: The maximum differences in volumetric dose were 19% and 13% for AXB and AAA respectively as shown in [Figure 1]. The average differences in the high dose (≥95% of prescribed dose) area were 8% for AXB and 6% for AAA, while those in the low dose (≤50% of prescribed dose) area were around 2% for both AXB and AAA. The results showed that the variation of dose distribution with/without CA did not meet more than 90% criterion for gamma index of 2%/2 mm. The passing rate was 86.5% and 81.0% for AXB and AAA in the gamma index histogram. It was shown that there was a significant difference in the high dose area. The dose uniformity in the high dose was within 1%, while there was a large difference in the spatial analysis of the dose distribution.
Figure 1: Volumetric dose deviation in phantoms

Click here to view

Discussion and Conclusion: The discrepancy of spatial dose distribution could be critical problem to choose the optimal treatment based on highly modulated VMAT plans. In conclusion, the effects of CA in the VMAT plan should be evaluated appropriately in the clinic, especially in where the beam passes through the contrast-sensitive organs such as liver, spleen, or kidneys with increased HU values due to CA.

Acknowledgement: This research was supported by a grant of the Korea Health technology R and D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health and Welfare, Republic of Korea (Grant Number: HI15C0638).

   P-28: Dosimetric Analysis of Plan Quality of Intensity-Modulated Radiation Therapy Versus Rapid Arc with Bone Marrow Sparing for Cervical Cancer Top

Vuppu Srinivas, Gangarapu Sri Krishna

MNJ Institute of Oncology and Regional Cancer Centre, Hyderabad, Telangana, India. E-mail: [email protected]

Objective: The aim of the present study was to compare intensity-modulated radiation therapy (IMRT) vs. Rapid Arc for treatment of cervical cancer with bone marrow sparing.

Materials and Methods: Fifteen cases of cervical cancer cases were selected for retrospective analysis. All the cases were previously treated using IMRT technique with bone marrow sparing (BMS-IMRT) as extra constraint. For this study, plans using Rapid Arc with bone Marrow sparing (BMS- RA) were created again for all patients following Radiation Therapy Oncology Group (RTOG) guidelines. The plan having coverage of 95% of PTV receiving 95% of prescribed dose is accepted. The plans were compared on the basis of planning target volume (PTV) coverage (dose to 2%, 98% of target), Constraints of OAR (Organs at Risk) were volume of 40% < 40 Gy for normal bladder and rectum, (volume receiving dose 5Gy) V5<95%, V10<80%, V20<60%, V30<50% and V40<35% respectively for Bone marrow were given for planning criteria. Apart from this, homogeneity index (HI), conformity index (CI) and Dose spillage index (R50%) was also calculated with respect to PTV coverage. The prescribed dose (PD) of 50Gy in 25 fractions was given.

Results and Discussion: Better PTV coverage with less OAR doses for bladder and rectum in case of Rapid Arc compared to IMRT. Bone marrow doses are comparable in both the techniques.

Conclusion: Using Rapid Arc technique better PTV coverage is possible with similar OAR doses compared to IMRT.

   P-29: Spatiotemporal Dose Evaluation in VMAT Plans for Prostate Cancer: Simultaneously Integrated Boost with Hypofractionated Schemes Top

Byung-Moon Park1, Yong-Ki Bae1,2, Min-Young Kang1,3, and Jeong-Woo Lee1,2

1Department of Radiation Oncology, Konkuk University Medical Center, 2Department of Convergent Medical Physics, Graduate School of Engineering, Konkuk University, 3Department of Medical Physics, Graduate School of Biomedical Engineering, Korea University, Seoul, Korea. E-mail: [email protected]

Introduction and Aim: As a prostate cancer is increasingly regarded to have a lower alpha/beta ratio (<1.5 Gy) with confidential intervals, contemporary randomized clinical studies have been suggested encouraging tumor control in hypofractionated dose schemes without significant late toxicity. To evaluate spatial and temporal effect of treatment schedule and dose optimization with simultaneously integrated boost (SIB) in volumetric modulate arc therapy (VMAT), dose distributions and effectiveness were compared with conventional 2-Gy based sequential VMAT.

Materials and Methods: Ten patients with prostate cancer were divided into two groups according to their prostate resection: intact prostate (Pint) and post-prostatectomy (Ptomy). The VMAT plans with sequential boost (VMAT-SEB) for the Ptomy were optimized to deliver dose of 46 Gy in 23 fractions to planning target volume including prostate bed and regional lymph nodes (PTV46). The boosting dose of 20 Gy was sequentially delivered more to prostate bed only (PTV66) in 10 fractions. While the VMAT plans with SIB (VMAT-SIB) were optimized to concurrently deliver dose of 46 Gy and 66 Gy to PTV46 and PTV66, respectively, in 23 fractions. The same dose scheme was remained for the PTV46 of the Pint, however, PTV including intact prostate cancer and seminal vesicles (PTV66) and high-risk PTV only (PTV76) were additionally defined. Total dose of 66 Gy in 10 fractions and 76 Gy in 5 fractions were delivered to each PTV sequentially in VMAT-SEB, whereas VMAT-SIB completed all dose delivery in 23 fractions. The spatial and temporal effect by non-uniform dose distributions and treatment schedule was evaluated with generalized equivalent uniform dose (gEUD), EUD-based equivalent dose in 2-Gy fractions (EEQD2), EUD-based tumor-control probability (TCP) and normal tissue complication probability (NTCP), and therapeutic efficiency for each organs of interest as well as physical evaluation.

Results: The VMAT-SIB achieved more conformal or competitive dose distributions with sparing irradiated volume of both bladder and rectum up to 3% at high and intermediate doses.

The rectal volumes received more than 60 Gy was effectively spared more than average 7%, especially for Pint. In addition, the hypofractionated scheme and dose optimization in the VMAT-SIB brought out promising improvement of biological effectiveness to both patient groups. The spatiotemporal effectiveness for the PTV showed increased EEQD2 more significantly with higher prescribed dose: 20 Gy for PTV66 of both groups and 30 Gy for PTV76 of Pint. Accordingly, EUD-based TCP was improved more than 20%, while the VMAT-SIB achieved comparable dose sparing of critical organs for Ptomy or slight increase EEQD2 and NTCP less than 3 Gy and 1.5%, respectively, for Pint. It led to increase therapeutic efficiency more than 20%.

Conclusion: In this study, the VMAT-SIB could provide optimized dose distribution to deliver differential prescribed doses to PTVs in hypofractionated schedule. The achieved spatiotemporal effectiveness of VMAT-SIB may allow treatment efficiency to potentially increase by significantly increasing EEQD2 of PTV and effectively sparing critical organs in prostate treatment.

Acknowledgement: This research was supported by a grant of the Korea Health Technology R and D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health and Welfare, Republic of Korea. (Grant Number: HI15C0638).

   P-30: Comparison of Rapid Arc, Helical Tomotherapy, Sliding Window IMRT and Conformal RT for Carcinoma Prostate Treatment Planning. Top

Amol Pawar, Kalpana Thakur1, Rajesh Kinhikar2, Sanjay Dhole3

Department of Radiation Oncology, Sir H N Reliance Foundation Hospital and Research Centre, 1Department of Radiation Oncology, Holy Spirit Hospital,2Department of Medical Physics, Tata Memorial Hospital, Mumbai, 3Department of Physics, University of Pune, Maharashtra, India. E-mail: [email protected]

Helical Tomotherapy (HT), a complex treatment strategy for intensity modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares Helical Tomotherapy against established RapidArc, IMRT and 3Dimensional conformal radiation therapy (3DCRT) delivery techniques.

Introduction: Objective: The potential benefits and limitations of the new RapidArc treatment concept compared to Helical Tomotherapy, fixed gantry intensity modulation techniques and conformal radiation treatment have been assessed at treatment planning level on ten patients presenting with prostate sites tumours.

Materials and Methods: CT datasets of ten patients were included in the study. Plans were optimised with the aim to assess organs at risk and healthy tissue sparing while enforcing highly conformal target coverage. Here we use simultaneous integrated boost technique. Planning objectives for PTV were: maximum significant dose lower than 64.2 Gy and minimum significant dose higher than 57 Gy and same for CTV were: significant dose lower than 70.88 Gy and minimum significant dose higher than 62.93 Gy. For organs at risk, the mean and median doses were constrained to be lower than 42-45Gy (rectum), 45-48Gy (bladder); additional objectives were set on various volume thresholds. Plans were evaluated on parameters derived from dose volume histograms. We were used Eclipse planning system to contouring the structure and generate rapidarc, IMRT & 3DCRT plans. For helical tomotherapy plans, we were used HI-Art Tomotherapy planning system. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D98% and D2% (dose encompassing 98% and 2% of the target volume respectively). The MU and delivery time were scored to measure expected treatment efficiency.

Results: Both helical tomotherapy and rapidarc resulted in better target coverage but helical tomotherapy had an improved homogeneity and conformity index as depicted in [Figure 1]. For RA/HT/IMRT/3D-CRT, mean CI was 1.0/1.0/1.0/1.0 &1.0/0.99/0.97/0.98 and HI was 0.03/0.05/0.03/0.03 & 0.11/0.16/0.12/0.06 for CTV & PTV respectively. For a prescribed dose of 66.25 Gy and 60 Gy to CTV and PTV respectively, mean doses to organs-at-risk (OAR) were 23.68Gy/24.55Gy/19.82Gy/23.56Gy for the bladder and 36.85Gy/33.18Gy/33.18Gy/38.67Gy for the rectum. D98% was 65.68Gy/66.23Gy/64.27Gy/61.56 for CTV and 59.54Gy/58.27Gy/57.95Gy/57.83Gy for PTV. D2% was 67.46Gy/69.72Gy/66.29Gy/59.53 for CTV and 66.13Gy/67.74Gy/64.99Gy/61.45Gy for PTV. Mean treatment time was 1.45 min/3.64 min /2.36 min /1.48 min.
Figure 1: Isodose distribution of 95 % of prescribed doses to PTV and CTV-P for (a) Helical tomotherapy (b) RapidArc (c) Sliding window intensity modulated radiation therapy (d) 3DCRT techniques

Click here to view

Conclusion: All approaches yield treatment plans of improved quality when compared to 3D conformal treatments, with helical tomotherapy providing best OAR sparing by using directional block method in planning and RapidArc being the most efficient treatment option in our comparison.

RapidArc was investigated for prostate sites cancer showing significant improvements in organs at risk and healthy tissue sparing with uncompromised target coverage leading to better conformal avoidance of treatments w.r.t. IMRT and 3DCRT. This, in combination with the confirmed short delivery time, can lead to clinically significant advances in the management of this highly aggressive cancer type. Clinical protocols are now advised to evaluate prospectively the potential benefit observed at the planning level. Plans which were calculated with 3DCRT provided good target coverage but resulted in higher dose to the rectum and bladder.

   P-31: Dosimetric Comparison for Active Breathing Coordinator Reduces Radiation Dose to the Heart and Lungs in patients with Left Breast Cancer using VMAT Techniques. Top

C. Prabagaran, S. S. Mokha, Piyush Jain, Gaurav Kumar, Chhamta Dutt, D. Manigandan1

Department of Radiotherapy, City Hospital and Research Centre, Jabalpur, Madhya Pradesh, 1Department of Radiotherapy, Medanta-The Medicity, Gurugram, Haryana, India. E-mail: [email protected]

Introduction: For women with left-sided breast cancer, there is risk of potential cardiotoxicity from the radiation therapy. Different breath-hold methods have been utilized. The two dominant methods are the spirometry-based active breathing coordinator (ABC R3.0) system (Elekta Ltd, Crawley, UK) and the video-based real-time position management (RPM) system (Varian Medical Systems, Palo Alto, USA). The ABC device was developed at the Manipal Hospital Vijayawada, AP. The device is essentially a mouth piece attached to a spirometer and the patient's nose is pegged to ensure they are breathing only through the device. As the spirometer is connected to a computer, the Radiation Teams are able to visualize the patient's level of inspiration. Once the patient has reached the required threshold, pinch valves in the spirometer remotely close, preventing the patient from exhaling or inhaling outside the required threshold. A wide array of planning techniques has been reported in the DIBH literature, but one planning study compared VMAT-Deep Inspiration Breath-Hold (DIBH) Technique and VMAT-Free-Breathing (FB) Technique. DIBH allows this potentially superior planning technique to be used while minimizing cardiac dose.

Materials and Methods: The Pinnacle treatment planning system, v.9.8 (Philips Radiation Oncology Systems, Fitchburg, WI) employs a collapsed cone convolution (CCC) algorithm method is currently regarded as one of the better practical options for dose calculation. Philips Pinnacle v9.8 TPS is used to generate VMAT plans, for a Elekta Infinity machine with a Agility 160 MLC (Elekta Ltd, Crawley, UK). Our VMAT planning protocol uses a single isocenter with two partial composite arcs, each consisting of two complementary arcs of identical gantry rotations. Again Plan is used to generate Free-Breathing (FB plans, for Infinity with a Pinnacle TPS. The plan quality was evaluated by dose conformity, homogeneity, dose fall-off and leakages. Efficiency is measured in treatment planning and delivery time. In order to investigate the dosimetric impact of the ABC, two sets of CT images were acquired.

Results and Discussion: Ten left-sided breast cancer cases are studied. The PTV volumes plan range from 534 to 620 cc. Plans were evaluated by target coverage, minimum and maximum dose to target, Quality of Coverage (QI), Homogeneity Index (HI) and conformity index (CI) as shown in [Table 1]. Dosimetric parameters for analysis included RTOG protocol in Heart, Left Lung, Right Lung, Greater Vessels, Opposite Breast, Liver, Spine max dose including Monitor Units (MU). Patient selection is long breath-hold 20-30 sec is desirable.
Table 1: 6 MV photon average dose for both volumetric modulated arc therapy (deep inspiration breath-hold) and volumetric modulated arc therapy (free-breathing) plans for all 10 patients

Click here to view

All plans were optimized using six megavolts (6 MV) X-ray, and the objective dose-volume parameters were identical at the beginning of optimization for the different plans, Planning study compared VMAT-Deep Inspiration Breath-Hold (DIBH) Technique and VMAT-Free-Breathing (FB) Technique. DIBH allows this potentially superior planning technique to be used while minimizing cardiac dose, Lungs dose etc. ABC is viable options to reducing margin for respiratory motion and main advantage was automated beam on and off during treatment of the patients without man interrupts the machine beam.

   P-32: Higher Homogeneity Index in Close Proximity Targets with Different Dose Prescription with VMAT Compare to IMRT Top

Jayapalan Krishnan1,2, Jayarama Shetty2, Suresh Rao1, Sanath Hegde1

1Department of Radiation Oncology, Mangalore Institute of Oncology, 2Department of Radiation Oncology, K.S. Hegde Medical Academy, Mangalore, Karnataka, India. E-mail: [email protected]

Introduction: Many advanced treatment delivery technologies like IMRT, VMAT, tomotherapy have been used widely in Radiotherapy. In the different delivery techniques, the relative merits of dosimetric advantage and the feasible treatment parameters play an important role in the decision making at the time of plan approval for clinical treatment. In the context of a plan with different levels of dose prescriptions for two or more targets, higher dose spillages are presented in the targets with lower dose prescription. This can be resulted an heterogeneous dose distribution. Therefore, the plan evaluation has to be carried out to identify the amount of homogeneous dose distribution in the targets with a lower dose prescription.

Objectives: Aim of this study was to analyse the homogeneity index with different levels of dose prescription to the close proximity targets using VMAT at different treatment sites and comparison of the same with IMRT.

Materials and Methods: 120 patients, includes 60 head and neck, 15 prostate, 20 cervix with Para aortic node, and 25 lower third oesophagus cancer patients. Two levels of dose was prescribed to the all patients in the all cases. The higher dose was to GTV target and lower dose was to CTV target. Dual arc VMAT and 7-9 field IMRT plans were generated for all the patients and optimized using similar planning objectives in Eclipse treatment planning system (10.0.39) for 6MV photons. Both plans were calculated using AAA at 2.5 mm grid size. Both the techniques VMAT and IMRT plans were evaluated based on the dosimetric score such as the Conformation Number (CN), Homogeneity Index (HI), Dose Gradient Index (DGI), and OARs sparing. Student 't' test was used to find out the significant difference between the techniques.

Results and Discussion: Results showed that conformity index, conformation number, and UDI of the higher dose prescribed target was significantly better with VMAT than IMRT plan (p<0.001) in all the sites. The average HI, coverage index of higher dose prescribed target of all sites did not differ significantly between VMAT and IMRT. However, the HI index of close proximity lower dose prescribed target was significantly better with VMAT plans than IMRT in all the sites (p < 0.001) without compromising target coverage. These results, implies that the dose fall-off with VMAT was more and resulted in sharp dose gradient to achieve homogeneity in close proximity target as well. This improved homogeneity effect in all the targets achieved with VMAT technique can avoid the risk of higher dose irradiation of serial organ with in the target as well as the clinical outcome can be assessed effectively.

   P-33: Weightage Optimization for the Hybrid VMAT For CA. Oropharynx Cancers Top

J. Antony Paull1, G. Madhan Kumar1, C. Krishnappan1,2, C. Anu Radha2

1Apollo CBCC Cancer Care, Gandhinagar, Gujarat, 2School of Advanced Sciences, VIT University, Vellore, Tamil Nadu, India. E-mail: [email protected]

Introduction: In India the head and neck cancer is over 40% of all cancers. In the western region the head and neck cancer is over 55% due to higher tobacco use. Treating such cancers by simple bilateral and anterior beams may restrict to deliver required dose due to the spinal cord. If a higher end technique like Intensity Modulated Radiation Therapy or Volumetric Modulated Arc Therapy is used then the dose to the uninvolved respiratory related structures like Larynx, Constrictor muscle, cervical esophagus, trachea and thyroid gland need to be compromised. So h-VMAT is the emerging technique to achieve the both objectives. But with h-VMAT the dose to lungs is comprised. So the vital role is plays by weightage optimization.

Objective: To optimize the weightage h-VMAT plans for Oropharynx cancers especially at the respiratory structures and lungs.

Materials and Methods: The 30 patients which have been treated earlier by VMAT technique are taken for the study. Delineation of PTVs and OARs and other respiration related structures were created by oncologist as per RTOG guidelines for Carcinoma of Oropharynx. Upper neck PTV was prescribed 60Gy in 30 fractions and lower neck PTV was prescribed 54Gy in 30#. Two h-VMAT plans are created for all the patients with the weightage of 80:20 and 40:60. h-VMAT plans were created at Eclipse treatment planning system with two mono isocentric plans in two steps. Dose calculations were performed by AAA (v11.01) algorithm with grid size of 2.5 mm. The isocentre was placed at the level of Larynx. as the first step, 80% of the prescribed dose the lower neck PTV was planned with static AP/PA fields with half-beam block technique and mid-line blocked by MLC to reduce the dose to the respiratory structures and to the spinal cord. as second step, a VMAT plan with two co-planar arcs for both upper and lower neck PTVs was created to deliver 100% dose to upper neck PTV and remaining 20% dose to Lower neck PTV by taking the AP/PA plan as a base dose plan during the optimization. The same procedure has repeated with the weightage changing of 40% at AP/PA fields and 60% at VMAT plans. As a prerequisite of the clinical acceptable plan, further DVH of respiratory structures and lungs are analyzed.

Results and Discussion: No significant variation at PTV, spinal cord and Parotids of all three types of plans. Significant variation is found at respiratory structures like larynx, PC Muscles, cervical esophagus, thyroid gland and trachea at hybrid plans in compared to VMAT plans. If further look at weightage variation the 80:20 plans has the edge over 40:60 in respiratory structures and lung dose. The DVH variation for all structure is shown in the [Table 1]. Our results show that h-VMAT doses are optimally reducing the dose to uninvolved structures like Larynx, PC Muscles, Cervical Esophagus, Thyroid gland and trachea in the treatment of Ca. Oropharynx over the VMAT. The weightage shared between the static field plan and VMAT in h-VMAT plan plays a vital role, care must be taken while deciding the dose prescribed in static field plan.
Table 1: The dose-volume histogram variation for all structure for three type of plans

Click here to view

   P-34: Comparitive Study of IMRT and VMAT for Cancer of Middle Third Oesophagus Top

C. Shambhavi, N. Jyothi1, Sarath Nair1, Shree Kripa Rao, B. Ramya1, G. C. Srinidhi1, Krishna Sharan1

1Department of Radiotherapy and Oncology, SOAHS, Kasturba Medical College, Manipal University, 2Department of Radiotherapy and Oncology, Kasturba Medical College, Manipal University, Manipal, Karnataka, India

Introduction: Radiotherapy plays a major role in the treatment of esophageal carcinoma. 3-Dimensional Conformal Radiotherapy (3DCRT) planning is the method of choice since many years. Innovative technologies in radiation delivery such as Intensity Modulated Radiotherapy (IMRT) offer potential for better tumor coverage reducing doses to normal tissues. The Volumetric Modulated Arc Therapy (VMAT), a novel form of IMRT allows intensity modulated radiation delivery during gantry rotation with dynamic multi leaf collimator (MLC) motion and dose rate alteration simultaneously.

Objective: The aim of this study is to determine the clinical impact of VMAT in middle third esophageal cancer and evaluate its various dosimetric indices by comparing with the IMRT.

Materials and Methods: Six patients with esophageal cancer were selected for this retrospective study. Planning CT scans were acquired with 5 mm slice thickness. The target, organs at risk (OARs) were then delineated. All plans were done in Monaco (version 5.1) planning system for Elekta Versa HD Linac with 80 pairs MLC for 6MV photon. A dose of 59.4Gy was prescribed to the planning target volume PTV59.4Gy and 45Gy to PTV45Gy in 33 fractions. 7-field IMRT, and single and double-arc VMAT plans were generated with the aim to spare OARs and healthy tissue while delivering highly conformal target dose. All plans aimed to achieve target coverage of 95% and hotspot within 107% of the prescribed dose. The objectives for OARs were as follows: spinal cord Dmax <45 Gy; and lung V20Gy<30%. And mean dose of Total lung <20 Gy; heart V45Gy <67%. Data analysis of plans were performed by means of DVH Statistics summary. For PTV59.4Gy and PTV45Gy, the values of D98% and D2%, minimum and maximum doses were reported. The Homogeneity Index (HI) in PTV59.4Gy was expressed in terms of (D2% - D98%)/D50%.

The degree of conformity of the plans measured with the Conformity Index (CI95%) expressed in terms of (TV95%/TV) was reported. Total MU (monitor unit) and treatment time in QA (quality assurance) mode also accounted. Maximum dose to spinal cord; Lung V5Gy, V20Gy; mean dose of Total lung; Heart V45Gy were reported. The analyzed dosimetric indices between groups were compared using student't' test and p value < 0.05 was considered significant.

Result: All the 6 patients for which IMRT and both VMAT plans showed good tumor coverage of 95% prescribed dose with better homogeneity and negligible hotspot. Coverage of PTV45Gy was significantly better with dual arc VMAT (p =0.045) than IMRT and single arc VMAT without compromising conformity and homogeneity. In all the plans the dose to the OARs were within the limit. Both single arc and dual arc VMAT resulted in considerable reduction in maximum dose to spine compared to IMRT (p-0.024, p-0.027 respectively) and also showed significant and closer to significant reduction in MU (p-0.012, p-0.09 respectively) and treatment time.

Discussion: In the treatment of mid third Esophagus, all group plans achieved better tumor coverage with OARs sparing. However, Spine dose was reduced by single and double arc was similar and significantly better than IMRT. The reduced treatment time and MU can help in patient convenience and throughput performance of LINAC.

   P-35: Dosimetric Advantages and Disadvantages of Junction Free VMAT Based Craniospinal Irradiation Technique Over the 3DCRT Technique Top

Saneg Krishnankutty, Biplab Sarkar

1Department of Radiation Oncology, Fortis Memorial Research Institute, Gurugram, Haryana, India. E-mail: [email protected]

Purpose: This article evaluates the dosimetric advantages and disadvantages of the junction free craniospinal irradiation over the 3DCRT technique. Further we compare the junctional characteristic of between two techniques.

Materials and Methods: CT datasets of 10 patients who have already received a VMAT based CSI treatment has been planned using a 3DCRT technique in this dosimetric study. Serial plans were generated with 3D conformal radiotherapy (3DCRT) as well as volumetric modulated arc therapy (VMAT) for a prescription dose of 35Gy in 21 fractions. To verify the junctional characteristic of the 3DCRT and VMAT plans Isocentre positions were manipulated both superiorly and inferiorly by ±1, ±2, ±3, ±5 mm to generate an overlap or gap at the field junction. 3DCRT based CSI contains two cranial ports along with the one or two spinal beams depending on the length of the spinal target volume. Junctions were matched using collimator, couch and gantry rotation. 3DCRT based CSI requires a junction shift to feather out the cold or hot spots at the junction. Junction shift requires three sets of planning segregated as the 1/3rd of the total prescription. For a three iso-centric plans the number of treatment and imaging beams is counted as 12 and 27 respectively. It's always challenging for a therapist to handle large number of beams in the Record and Verify (R and V) system. VMAT based CSI uses a full arc (360°) cranial beam with 100° posterior arc (either one or two depending on the PTV length) for spinal target. Optimization was carried out for all isocentre in a synchronized setting. An unrestricted jaw movement was used to generate a low gradient junction over a length of more than 10 cm.

Results: Both with inferior and superior isocentric shifts, 3DCRT showed higher dose variation at the junction when compared with VMAT. With a 5 mm superior shift (creating gap between fields) there was average junctional underdose of 13.9 ±2.1 Gy and 4.8 ± 1.4 Gy for 3-D CRT and VMAT respectively. With a 5 mm overlap, 3D CRT and VMAT plans showed an overdosing of 10.3±2.5 Gy and 6.0±1.5 Gy respectively. For D1%_Spine statistically significant dose difference was obtained at -3 mm and -5 mm level. 1% dose to brain was not statistically different between 3DCRT and VMAT plans (0.4≤p≤0.9). Highest dose point between 3DCRT and VMAT shows a significant dose variation (0.03≤p≤0.001). Total 22 OAR's were evaluated dosimetrically between two plans. Midline structures like heart, esophagus and thyroid shows a higher dose in case of 3DCRT where the peripheral structure like kidney, liver shows an elevated dose for VMAT plans. However difference in dose to OAR attributed to different techniques are not statistically significant except thyroid. 3DCRT shows a lesser dose to (body-PTV) in <7Gy range, however above 10Gy 3DCRT spillage dose was higher than VMAT. VMAT require 2.2 times higher MU than 3DCRT required MU.

Conclusion: The low dose gradient junction based VMAT techniques do not have a specific junction hence insensitive to patient longitudinal setup error (1-3 mm). Unlike deliberate shifting of junction every 7th fraction with 3DCRT the low gradient technique does not require junction shifting during entire CSI course. VMAT shows a higher spillage dose than 3DCRT in the low dose range. VMAT require only 4 treatment and nine setup beams compared to 12 and 27 beams respectively for 3DCRT. 3DCRT demands an exact spatial position of the patient for reproducibility of the junction where the proposed junction free VMAT technique is insensitive to the accurate patient positioning; hence number of portal images or CBCT/isocentre/day can be reduced. OAR doses yields a mixed result with favoring VMAT technique.

   P-36: Influence of Statistical Uncertainty on Monte Carlo Dose Calculation in Volumetric Modulated Arc Therapy for Glioblastoma Brain Tumor Top

P. Mohandass1,2, D. Khanna2, D. Manigandan1, Midhun Kumar1, Narendra Bhalla1, Abhishek Puri1, Pawan Kumar1

1Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, 2Department of Physics, School of Science and Humanities, Karunya University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: Volumetric modulated arc therapy (VMAT) is an advanced modality of radiotherapy treatment delivery by varying gantry speed and dose rate with reduced treatment time. Dose calculation accuracy in radiotherapy is an important and crucial factor to prevent mistreatment of radiation treatment delivery. Ideally, the dose calculation algorithm should be accurate and able to generate quality plan with less calculation time. Although Monte Carlo (MC) dose calculation algorithms are recognized as the most accurate dose computation algorithms among the commercially available algorithms for treatment planning, its inherent statistical uncertainty (SU), determines the accuracy of the dose calculation and calculation time. During VMAT treatment, the Monaco™ treatment planning system (TPS) has an option to choose different SU (%) up to 5% for MC dose calculations. So it is necessary to evaluate optimal acceptance level of SU (%) for different treatment each clinical sites.

Objectives: To study the dosimetric impact of statistical uncertainty per plan on Monte Carlo calculation in Monaco™ TPS during VMAT for glioblastoma brain tumor.

Materials and Methods: Five glioblastoma (GBM) brain tumor patients treated with 60Gy/30 fractions were chosen for the study. VMAT plans were generated with Monaco™ treatment planning system (TPS-V5.11) for Elekta Synergy™ linear accelerator with 1 cm leaf width. Plans were generated using dual partial arcs with 2% statistical uncertainty per plan. By keeping all other parameters constant, plans were recalculated only by varying the SU, 0.5, 1, 3, 4, and 5%. For plan evaluation, conformity index (CI), Homogeneity index (HI) to planning target volume (PTV), dose coverage to PTV (D98%) was analyzed. The mean and max dose to organ at risk (OAR) was analyzed for brain stem, optical structures, and PTV–brain. The normal tissue volume receiving dose >5Gy and >10Gy and normal tissue integral dose (NTID) (patient volume-PTV), calculation time (mins), point dose measurement and gamma pass rate (<1.00) (3%/3 mm) were compared.

Results and Discussion: The CI and HI improve as the SU increases 0.5 to 5% (p>0.05). No significant dose difference was observed in Dmean, D98% to PTV, mean dose to brain stem, optical structures and PTV–brain (p>0.05). The Dmax to PTV, optic structures and brain stem were increases with increase of SU (p<0.05). Similarly, normal tissue volume receiving dose >5Gy and >10Gy and NTID showed no significant dose difference (p>0.05). Decrease in dose calculation time was observed with increase of SU (p<0.05). Gamma pass rates were observed >98% and <3% variations in point dose measurement in all VMAT plans. No significant dose variation was seen in calculation reproducibility (p>0.05).

The SU can be accepted up to 3% per plan with reduced calculation time without compromising target coverage, OAR doses and plan delivery for GBM VMAT plans. Only by accepting variations in point dose and inhomogeneous dose within target. There is no significant dose variation in calculation reproducibility.

   P-37: Planning Comparison Between Dynamic IMRT, Single and Dual Arc Volumetric Modulated Arc Radiotherapy for Head And Neck Carcinoma Using a Simultaneous Integrated Boost Technique Top

C. Prabagaran1, S. S. Mokha1, Piyush Jain1, Gaurav Kumar1, Chhamta Dutt1, D. Manigandan2

1Department of Radiotherapy, City Hospital and Research Centre, Jabalpur, Madhya Pradesh, 2Department of Radiotherapy, Medanta-The Medicity, Gurugram, Haryana, India. E-mail: [email protected]

Introduction: Compared to dynamic beam Intensity-Modulated Radiation Therapy (IMRT), the main advantage of Volumetric Modulated Arc Therapy (VMAT) is a shortened delivery time, which leads to improved patient comfort and possibly smaller intra-fraction movements. This study aims at a treatment planner-independent comparison of radiotherapy treatment planning of IMRT and VMAT for head-and-neck cancer performed based on the same CT- and contouring data. Radiotherapy for head and neck cancer can be challenging due to the complex anatomy of the head and neck region with these tumours often located within close proximity to critical structures which can limit radiation dose. Furthermore the ability of dynamic IMRT to produce inhomogeneous dose distributions can be exploited to simultaneously treat the primary and elective target volumes to different dose per fractions without increasing overall treatment time. This SIB technique allows both volumes to be treated within one treatment plan without the need for matching fields therefore reducing the potential risk of reduced dose coverage in the areas of matching beams.

Materials and Methods: The Monaco Treatment Planning System, v.5.1 (Elekta Ltd, Crawley, UK) employs a Monte-Carlo algorithm method is currently regarded as one of the better practical options for dose calculation. Elekta Monaco v5.1 TPS is used to generate VMAT plans, for a Elekta Synergy Platform Linear Accelerator Machine with a Agility Head 160 MLC (Elekta Ltd, Crawley, UK). 20 patients with loco regionally advanced the oropharynx, hypopharynx and larynx carcinoma were selected. The prescription dose was 70, 63 and 56 Gy to the high-dose, intermediate-dose and low-dose planning target volume (PTV), respectively, and planning parameters were according to Radiation Therapy Oncology Group IMRT protocols. VMAT and IMRT plans were calculated, and dose-volume histograms were created for plan evaluation and comparison. The VMAT delivered the dose rapidly with lesser Monitor Unit without compromising in target dose coverage, conformity and higher sparing of OARs than IMRT.

Results and Discussion: We compared single and double arc VMAT with 7-field fixed dynamic IMRT (SW) in 20 patients with advanced tumours of the oropharynx, hypopharynx and larynx and data presented in [Table 1]. The PTV coverage was similar between IMRT and VMAT with improved homogeneity when using two arcs with VMAT. Similarly there were no significant differences in the doses to the OARs, a slightly lower mean dose to the parotid glands with the double arc VMAT plans compared with the single arc and IMRT plans. Which compared single and double arc VMAT with 7 field fixed field dynamic IMRT (SW) in 20 patients with tumours of the oropharynx, hypopharynx and larynx. PTV coverage and conformity were similar in the two groups with better homogeneity in the double arc VMAT plans. In this study, the mean doses to the OARs were lower in the VMAT plans with double arc plans achieving significantly lower doses compared with single arc plans. For the spinal cord, the max dose was 33 Gy in the double arc VMAT plans and 35 Gy in the dynamic IMRT plans. For the brainstem max dose was 36.4 Gy for double arc VMAT and 39.1 Gy for dynamic IMRT. For the right side parotid glands, the mean dose was 22.3 Gy for double arc VMAT and 25.1 Gy for dynamic IMRT, while for the left side parotid glands the mean dose was 21.2 Gy and 23.6 Gy for the double arc VMAT and dynamic IMRT plans, respectively. Additional OARs, including cochlea, vocal apparatus and eyes constrictors, were also defined and evaluated in this study. Again there was greater sparing of these OARs with the VMAT plans achieving lower mean doses to these structures. Integral doses to the body were also lower in the VMAT plans by compared with the fixed field dynamic IMRT plans. Simultaneous integrated boost VMAT achieved comparable plans to dynamic IMRT in complex head and neck cases and used two-thirds less monitor units.
Table 1 : 6 MV photon average dose volume statistics comparing dynamic intensity-modulated radiation therapy, single arc volumetric modulated arc therapy and dual arc volumetric modulated arc therapy plans for all 20 patients

Click here to view

   P-38: Investigation of Effect of Collimator Angles on Dosimetric Parameters in Double-Arc Volumetric Modulated Arc Therapy of Head and Neck Cancer Top

Shefali Pahwa1, Avtar Singh1, Amit Saini1, Tapas Kumar Dora1, D. D. Deshpande2

1Department of Radiotherapy, Homi Bhabha Cancer Hospital, Sangrur, Punjab, 2Department of Medical Physics, Tata Memorial Hospital, Parel, Mumbai, India. E-mail: [email protected]

Introduction: Volumetric Modulated Arc Therapy (VMAT) has become a technique of choice these days for almost all the treatment sites. Arc therapy technique which was originally developed for prostate, subsequently extended to all the sites like Head and Neck, Brain, abdomen, thorax and cervix. VMAT technology coordinates gantry rotation speed, multileaf collimator (MLC) motion, and dose rate modulation simultaneously. The advantage of VMAT technique is that highly conformal treatment is possible with optimal sparing of critical structures and with lesser overall treatment time, lesser monitor units (MU's) and more efficiency as compared to static gantry angle Intensity Modulated Radiotherapy (IMRT).

Aim and Objective: The aim of this study is to investigate the effect of different collimator angles on dosimetric parameters in double arc volumetric arc therapy of Head and Neck cancers. The collimator angle has the largest impact and is worth considering, so, its awareness is essential for a planner to produce an optimal VMAT plan in a reasonable time frame.

Materials and Methods: Fifteen patients undergoing VMAT for Head and Neck cancers are included in this study. Double-arc VMAT plans are created using Monaco® treatment planning system (version 5.11) with two full arcs i.e. one is clockwise arc and other is anticlockwise arc with collimator angle 0–0°. The plans are reoptimized with different collimator angles like 15–345°, 30–330°, 45–315°, 60–300°, 75–285°, 90–270°, 0–90°, 5–85°, 10-80°, 15– 75°, 30–60° and 45–45° using same optimization parameters. The conformity index (CI), homogeneity index (HI), gradient index (GI), machine monitor units (MUs), dose-volume histogram and mean and maximum dose of the PTV are calculated and analyzed. On the other hand, the dose-volume histogram and mean and maximum doses of the OARs such as the parotids, PRV spinal cord, brainstem and oral cavity for different collimator angles are determined from the plans.

Result and Discussion: Preliminary results show that dose coverage of target and OAR's doses depend significantly on the collimator angles due to the geometry of target and OAR's. These dosimetric results provide support and guidance to allow the clinical radiation physicists to make careful decisions in implementing suitable collimator angles to improve the PTV coverage and OARs sparing in Head and Neck VMAT.

Study is going on. Detailed results will be presented in full paper.

   P-39: Dosimetric Evaluation of Dose Reporting Modes in monaco TPS: Dose to Medium VS Dose to Water Top

Mamta Mahur1,2, P. S. Negi1, R. K. Grover1, M. Sasindran1, V. Gedam1, R. Sharma1, A. Singh1, D. Kumar1, M. Semwal3, Munendra Singh2

1Delhi State Cancer Institutes, 3Army Hospital (RR), New Delhi, 2School of Basic Sciences and Research, Sharda University, Greater Noida,Uttar Pradesh, India. E-mail: [email protected]

Introduction: In radiation therapy treatment planning accuracy of dose calculation is crucial to achieve the clinical goal of radiotherapy i.e. to maximize tumour control probability and to minimise normal tissue complication probability. In radiotherapy treatment planning systems (TPS), photon dose calculations are performed including both simple correction based algorithm and model based algorithm and typically report the dose to water. With recent advancement in technology and computing power, improved Monte Carlo codes have been developed and employed in modern radiotherapy TPS for clinical practices.

Monte Carlo based dose calculations are considered as gold standard due to its accuracy in computing. Monte Carlo algorithm also has the ability to calculate energy deposition in different media accurately and reports dose to medium directly instead of dose to water as what conventional dose calculation algorithm does.

Objective: Monte Carlo dose calculation algorithm is available for external beam photon dose calculations in MONACO treatment planning system (TPS) v 5.11.01 which can report the absorbed dose in two modes: dose-to-water (Dw) and dose-to-medium (Dm). The main purpose of this study is to compare the dosimetric results of two dose reporting modes of Monte Carlo algorithm in MONACO TPS and clinical evaluation in real patient treatment plans of Ca Esophagus case.

Materials and Methods: Step and Shoot IMRT treatment plans were created in Monaco TPS using Monte Carlo algorithm for ten cases of Ca Esophagus for a dose of 5400cGy in 30 fractions using 6MV photon beam for ONCOR Expression linear accelerator. Treatment plans were computed using Dose to medium and Dose to water for identical beam arrangements, grid size and dosimetric constraints. Dosimetric evaluation of plans were done by comparing various dosimetric parameters in the plans for both the dose reporting modes.

Results and Conclusion: The preliminary comparative analysis of dosimetric results in our clinical study shows that selection of either Dw or Dm in Monte Carlo calculations in IMRT plans in MONACO TPS does not introduce significant dosimetric difference in target coverage and OAR DVH's. However doses reported in Dw were relatively higher in comparision to doses reported in Dm plans.

   P-40: Evaluation of FFF Beam in Head and Neck Cancer for Rapid Arc Delivery Top

Sandip Patil, Vaibhav Mhatre, Shaju Pilakkal, Rajkumar Chauhan, M. Vadivel, Kaustav Talpatra, Pranav Chadha

Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital and Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Objective: Aim of this study was to investigate the applicability of flattening filter free (FFF) beams to fractionated radiotherapy of head and neck cancer.

Materials and Methods: Five head and neck cancer patients previously treated were selected for this study. All patients were treated on Edge linear accelerator which was recently installed at our Institute. Each plan was optimized for Rapid Arc therapy (RAT) using 2 full arcs on Eclipse Planning System v13.6. Prescription doses are 60 Gy to the primary and 54 Gy to the nodal target in 30 fractions. For each patient two plans were created by varying the photon beam energy (6X vs 6X FFF) for maximum dose rate 600 MU/min for 6X and 1400 MU/min for 6X FFF. For each patient the prescription dose and OAR dose limits remained unchanged. Furthermore, the number of optimization iterations remained the same for each plan without user interference. The plans were compared using dose volume histograms, conformity and homogeneity indices.

For the PTV, the homogeneity index (HI) and conformity index (CI) were used as comparison metrics between FFF-RAT, FF-RAT plans. HI was defined as (Dmax)/Dp, where Dmax is the maximum dose received, Dp is the prescribed dose. CI was calculated as Vpi/PTV, where Vpi, and PTV represent the volume receiving a dose equal to or greater than the prescribed dose and PTV volume, respectively.

In the evaluation of the OAR dose, the maximum point doses to the spinal cord and brain stem were determined, and the mean doses to the parotid gland, larynx, and body were recorded. Finally, the number of MUs and the beam-on time (BOT) were evaluated for comparisons of the delivery efficiency.

Results: All plans met the clinical objectives. The RAT plan quality for 6X FFF (1.27) is similar to 6X (1.28). The mean doses for both the paratoids were almost similar. The FFF beams produce slightly better sparing for OARs such as brainstem and larynx. Total MUs are slightly higher in 6X-FFF compared with 6X. The mean body dose was lower in FFF.

Conclusion: For Head and Neck Cancers with conventional fractionation, FFF beam have little impact on Rapid Arc in terms of delivery, plan quality and OAR doses when compared with Flattened beam.

   P-41: Comparision of Radiation Treatment Plans for Breast Cancer Between VMAT and IMRT Top

N. Jyothi, C. Shambhavi, B. Ramya, G. C. Srinidhi, S. Sarath Nair, Shree Kripa Rao, Krishna Sharan

Department of Radiotherapy and Oncology, Kasturba Medical College, Manipal University, Manipal, Karnataka, India. E-mail: [email protected]

Introduction: Breast cancer most common cancer in women. Radiotherapy following breast-conserving surgery (BCS) is currently the standard treatment for patients with early breast cancer. The main purpose is to improve local control in treated breast with minimum toxicity. With the advent of advanced sophisticated treatment planning software, Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy is becoming increasingly popular.

Objective: The aim of this study is to compare and analyzing the dosimetric aspects of Intensity Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) for Cancer of breast cases.

Materials and Methods: A total of Ten (10) patients who have under gone breast conservative surgery for breast cancer were considered for this study. CT images of the required region was acquired with slice thickness of 5 mm with sixteen slice Computed Tomography (CT) available at our center. After CT scan was done the DICOM images were transferred to treatment planning system. Clinical Target Volume (CTV), Planning Target Volume (PTV) and Organ at Risk (OAR) volumes were generated by Radiation Oncologist according to ICRU83 guidelines. PTV was excluded 3 mm from skin. All plans were generated in Monaco planning system version 5.1 using 6 MV X-RAY beam For Elekta HD versa linear accelerator integrated with 80 pairs of Multi Leaf Collimator (MLC). The dose prescribed was 50Gy in 25# to the PTV. Both VMAT (dual arc) and IMRT (7 fields) plans the dose calculation is done by using Monte Carlo Photon algorithm. Tissue heterogeneity correction was considered in the TPS optimization process. All plans were done to achieve a minimum of 95% of the prescribed dose to 95% Target volume. Plans were compared using Dose Volume Histogram (c-DVH) for maximum dose, Homogeneity Index (HI) and Conformity Index (CI) of the PTV as well as dose to OARs. The target dose uniformity and conformity are calculated and evaluated based on ICRU 83. The conformity index (CI) as defined in ICRU is CI = Volume of PTV covered by the reference isodose/Volume of PTV. CI = 1.0 is ideal value. The Homogeneity Index (HI) as defined in ICRU is HI = (D 2% - D 98%) / D 50%. HI = 0 (Zero) is ideal value.

Results: All the plans achieved minimum target coverage of 95% of the prescribed dose to 95% of the target volume. The dose to OARS are very low in VMAT than the IMRT plans. V10, V20, V5, Maximum dose, Mean dose for Ipsilataral lung are low in VAMT. Contralateral Lung, Total lungs, contralateral breast, Mean doses are low in VMAT compared to IMRT. Heart V10, V20, V25 are also low in VMAT plans. There is no significant difference interms of Tumor coverage, HI, CI in both the techniques. Maximum Dose to PTV and Monitor units are low in VMAT technique.

Conclusions: By comparing both the techniques though the CI, HI are similar, but the Dose to normal tissues are better spared in VAMT than the IMRT Treatment planning technique. Lesser monitor units in VMAT planning reduced the treatment time.

   P-42: Dosimetric Impact of Statistical Uncertainty Per Control Point on Monte Carlo Dose Calculation in Monaco TPS Volumetric Modulated Arc Therapy for Lung Cancer Top

P. Mohandass1,2, D. Khanna2, D. Manigandan1, Midhun Kumar1, Narendra Bhalla1, Abhishek Puri1, Pawan Kumar1

1Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, 2Department of Physics, School of Science and Humanities, Karunya University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: The Monte Carlo calculations (MC) are potentially more accurate than the best currently available commercial algorithms. However, Monte Carlo calculations inherently contain random errors, or statistical uncertainty (SU), the level of which decreases inversely with the square root of computation time. The Monaco treatment planning system (TPS) uses MC calculation algorithm for the patient dose calculation in external beam radiotherapy beams. It has an option to choose different SU (%) per control point up to 10% during dose calculations. Therefore, to generate clinically acceptable plans with lesser time, the compromise between SU and dose calculation time must be understood and studied properly for various treatment sites.

Objectives: To study the dosimetric impact of statistical uncertainty per control point on Monte Carlo calculation in Monaco™ TPS during volumetric modulated arc therapy (VMAT) for lung cancer.

Materials and Methods: Five lung cancer patients treated with 60Gy/30 fractions were chosen for the study. VMAT plans were generated with Monaco™ treatment planning system (TPS-V5.11) for Elekta Synergy™ linear accelerator with 1 cm leaf width. Plans were generated using dual partial arcs with 5% statistical uncertainty per control point. By keeping all other parameters constant, plans were recalculated only by varying the SU, 1, 2, 3, 4, 6, 7, 8, 9, and 10%. For plan evaluation, conformity index (CI), Homogeneity index (HI) to planning target volume (PTV), dose coverage to PTV (D98%) was analyzed. Mean and max dose to organ at risk (OAR) was analyzed for spinal cord, pericardium, both lungs-PTV, esophagus and liver. The normal tissue volume receiving dose >5Gy and >10Gy and normal tissue integral dose (NTID) (patient volume-PTV), calculation time (mins), point dose, gamma pass rate (<1.00)(3%/3 mm) were compared. In addition, calculation reproducibility was analyzed.

Results and Discussion: CI and HI improve as the SU increases 1 to 10% (p>0.05). No significant dose difference was observed in Dmean to PTV, both lungs-PTV dose, mean dose to pericardium, esophagus and liver (p>0.05). Similarly, normal tissue volume receiving dose >5Gy and >10Gy and NTID showed no significant dose difference (p>0.05). Decrease in dose calculation time was observed with increase of SU (p<0.05). The Dmax to PTV and spinal cord was increases with increase of SU (p<0.05). The gamma pass rates were observed >97% and <3% variations in point dose verification in all VMAT plans. No significant dose variation was seen in calculation reproducibility (p>0.05).

The SU can be accepted between 4-7% per control point with reduced calculation time without compromising target coverage, OAR doses and plan delivery for lung VMAT plans. Only by accepting variations in point dose and inhomogeneous dose within target. There was no significant dose difference in calculation reproducibility.

P 43 ABS0051

   P-43: Verification of Monitor Unit Calculations for Eclipse Treatment Planning System by In-House Developed Spreadsheet Top

M. Athiyaman, Hemalatha, Arun Chogule1, H. S. Kumar2

Departments of Radiological Physics and 1Radiotherapy S.P. Medical College and AG Hospitals, Bikaner, 2Department of Radiological Physics, S.M.S Medical College, Jaipur, Rajasthan, India. E-mail: [email protected]

Introduction: Computerized treatment planning is a rapidly evolving modality depends efficiently on hardware and software. Despite various ICRU recommendations suggest 5% deviation in dose delivery the overall uncertainty shall be less than 3.5% as suggested by B.J. Minjnheer. J. To ensure accurate dose delivery to the patients independent or secondary verification of Monitor Units (MU) check is preferred. In house spread sheets are developed by the clinical medical physicist to cross verify the dose calculated by the TPS. The Task Group 40 and 114 recommends that the calculation results of any TPS should be independently verified.

Objective: To develop an in-house spreadsheet for the secondary monitor unit verification for our Linear Accelerator for 6MV X-ray beams.

Materials and Methods: The Monitor unit verification calculation (MUVC) verification was tested for pre-approved and executed treatment plans taken from our Treatment Planning System (TPS) database (Make: Varian Medical System, Model, Eclipse version 13.7). The treatment plans were made for Linear Accelerator (Make: Varian Medical Systems, Clinac 2100CD, Palo Alto, CA) with integrated 80 leaf Multileaf collimator for 6MV X-ray beams. In house developed spreadsheet based on MS Excel was used in this study. The necessary dose calculation parameters such as Output Factor (O.F), Percentage Depth Dose (PDD) and off axis ratio (OAR) data were taken from the TPS. The TPS calculated MU for square fields, wedged fields, Head and Neck, Esophagus and Cervix cases were cross verified with the spreadsheet.

Results: MU ratio for square fields for fixed SSD technique and isocentre beams were within acceptable range for the taken depths of 5 cm, 10 cm and 15 cm. The overall MU ratio lies in the range of 0.999 to 1.02 for square field geometries which showed that there was a deviation of 1% between the TPS calculated and the spread sheet calculated. The MU ratios were 0.995 for Head and Neck plans and 1.012 for Cervix plans with a standard deviation of 0.024 and 0.029 respectively.

However we observed the mean MU ratio for Esophagus plans were 1.026 with the standard deviation of 0.040.

Discussion: The independent spreadsheet was designed and tested for most of the routine treatment sites and geometries. The designed spreadsheet is having good agreement with the Eclipse TPS version 13.8 for homogenous treatment sites such as Head and Neck and Cervix and it can be used a secondary MU verification tool.

   P-44: A Dosimetric Feasibility Study on Flat and Unflat Beams in VMAT Delivery of Nasopharynx Cancers Top

S. Maruthu Pandian, S. Karthikeyan, J. Mathangi, T. Surendra Reddy1

Department of Radiation Oncology, BGS Global Hospitals, Bengaluru, Karnataka, India. E-mail: [email protected]

Purpose: To evaluate Rapid Arc - volumetric modulated arc radiotherapy (VMAT) using coplanar arcs for the treatment of nasopharynx (NPx) carcinomas to achieve conformal dose distribution, homogeneous coverage of the planned target volume (PTV) using flattened beams (FF) and flattening filter free (FFF) beams. The purpose of this work is to evaluate any potential improvement in Rapid Arc plans using Flattening Filter Beams. This work represents one of the initial attempts to assess the usefulness of evaluating normal tissue dose reduction in dynamic VMAT using FFF beams on the True beam STx platform.

Methods: We use the Eclipse (version 13.7) and Truebeam STx linear accelerator which allows during VMAT delivery for both FF and FFF beams. We considered 25 NPx patients who underwent FF VMAT delivery. We set the collimator between 15o and 30o and generate plans with and without flattening filter for comparison. Special attention is given to the low dose regions. Clinical radiation treatment plans were converted to plans with the FFF plans g. Each plan with FFF beams were planned to obtain target coverage within 1% of that in the original FF plan. The new plans were compared to the original plans in a Varian Eclipse treatment planning system (TPS). Reduction in normal tissue dose was evaluated in the new plan by using the parameters V5, V10, and V20 in the cumulative dose-volume histogram for the following structures: Brainstem, Chiasm, Brain, Spinal cord, Parotids. Cochlea, Oral Cavity, Larynx and Mandible. In order to validate the accuracy of our beam model, MLC transmission measurements were made and compared to those predicted by the TPS.

Results: The greatest change between the original plan and new plan occurred at lower dose levels. The reduction in V20 was never more than 1.2% and was typically less than 1% for all patients. The reduction in V10 was never more than 1.6% and was typically less than 0.8% for all patients. The reduction in V5 was 1.2% maximum and was typically less than 0.5% for all patients. The variation in normal tissue dose reduction was not predictable, and we found no clear parameters that indicated which patients would benefit most from FFF beams. As expected FFF beams has 27% higher Monitor Units (MU) as compared to FF beams. Our TPS model of MLC transmission agreed with measurements with absolute transmission differences of less than 0.1% and thus uncertainties in the model did not contribute significantly to the uncertainty in the dose determination.

Conclusion: The amount of dose reduction achieved was not significant in VMAT delivery of FFF beams appears to be similar and not more than 2%. Currently we are analysing more plans for other sites and with other geometries to improve the statistical significance of our conclusion.

   P-45: Impact of Different Collimator Angles on Dosimetric Outcome of Rapid-Arc Plans Top

Hemant Umbrani, Sadique Kazi, Anand Gudur

Krishna Hospital and Medical Research Center, Karad, Maharashtra, India. E-mail: [email protected]

Introduction: Dual arc Rapid-Arc™ treatment plans were mainly planned by assigning two different collimator angles. Generally both collimator angles were complement to each other. Present dosimetry study compares dual arc Rapid-Arc™ plans using various collimator angles set for each arc. Plans were compared using Dose Homogeneity Index and Dose Spillage Index.

Objective: To compare and study impact of various collimator angle settings on Dose Homogeneity Index and Dose Spillage Index for Rapid-Arc™ treatment planning.

Materials and Methods: Five head and neck cancer patients were selected for this dosimetric study. Five different dual arc Rapid-Arc™ plans were generated for each patient. These plans were generated with collimator angles values 10°-350°, 25°-25°, 25°-325°, 35°-325°, 45°-315° respectively for each patients. While gantry start and stop angles, field size, dose rate and optimization parameters were kept same for each plan of particular patient. Dual arc Rapid-Arc™ plan optimization was performed using Progressive Resolution Optimiser algorithm (Varian Medical System, Palo Alto, USA). Dose calculations were performed using 6 MV photons and algorithm used was Anisotropical Analytical Algorithm (Varian Medical System, Palo Alto, USA) in Eclipse treatment planning system. Comparison were made using Dose Homogeneity Index and Dose Spillage Index. Dose Homogeneity Index (DHI) is defined as, DHI= (D5-D95)/prescription dose. D5 and D95 were minimum doses to 5% and 95% of PTV respectively. Dose Spillage Index (R50%) was defined as, R50%=50% isodose volume/PTV volume. Smaller the value of DHI more is the homogeneous distribution in PTV. Lower R50% ratio indicates greater dose fall-off and better dose conformity around the PTV.

Result: DHI were found 0.0851 ± 0.00331, 0.08451 ±0.00321, 0.07467 ± 0.00316, 0.08379 ± 0.00303, 0.08245 ± 0.00411 respectively. DHI found higher in 10°-350° collimator angles plan than 45°-315° or 35°-325° plans. R50% were found 2.4255 ± 0.02489, 2.7418 ± 0.05185, 2.6428 ± 0.08001, 2.8339 ± 0.16329, 2.0775 ± 0.03118 respectively. R50% found more in 10°-350° collimator angles plan than 45°-315° or 35°-325° plans.

Discussion: By performing this dosimetric study it was observed that both Dose Homogeneity Index and Dose Spillage Index can be improved with different collimator angles value. We get better results in 35°-325° and 45°-315° collimator angle combinations in terms of homogeneity and dose spillage.

   P-46: A Dosimetric Comparative Analysis of Tomo-Direct 3DCRT and Conventional 3DCRT in Case of Left-Sided Breast Cancer Top

Priya Saini, Ritesh Mhatre, Shrikant Kale, D. D. Deshpande

Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India. E-mail: [email protected]

Objective: Comparing the Dosimetric parameters of TomoDirect (TD) 3DCRT with Tomotherapy and Conventional 3DCRT on Eclipse Treatment panning systems for carcinoma of left sided breast.

Methods: 10 patients with left-sided breast cancer were selected for this study who had received whole breast radiotherapy following breast-conserving surgery. 3DCRT treatment plans were generated with Linear Accelerator on Eclipse TPS and TD-3DCRT on Tomotherapy TPS. Planning target Volume (PTV) andorgan at risk (OAR) such as lung and heart were contoured. The Hypo fractionated treatment regimen was used to prescribe the dose to the planning target volume (PTV), i.e. 40 Gy in 15 fractions. The treatment Plans were compared using to dose-volume histogram analysis in term of PTV coverage, HomogeneityIndex (HI), Conformity Index (CI) and dose to OARs.

Results : TomoDirect-3DCRT showed PTV coverage better than Linear accelerator based 3D-CRT. There was no significant difference in the mean PTV dose between 3DCRT and TD-3DCRT. Conformity of PTV was better in 3DCRT than that in TD-3DCRT (Mean CI 1.2 ± 0.08 vs. 1.7 ± 0.34, p=0.0005). However, homogeneity of PTV was better in TD-3DCRT than in 3DCRT (Mean HI 0.06 ± 0.039 vs. 0.13 ± 0.044, p=0.005). For ipsilateral lung, values of V5Gy, V10Gy, V12Gy, V20Gy and V30Gy were significantly lower in 3DCRT than those in TD-3CDRT. For heart, mean value of V2.5Gyin 3DCRT was lower than that in TD-3CDRT (Mean10.8 ± 9.45 vs. 14.8 ± 4.19, p=0.0001) and V105% of PTV was also found to be lower in 3DCRT than in TD-3CDRT. It was also found that, with increasing of CLD (1 Cm to 2.5 Cm), percentage volume receiving V12Gyof ipsilateral Lung was also increasing for both modalities.

Conclusion: The study showed that doses to OARs were lower for 3DCRT technique and higher for TD-3CDRT. The PTV coverage in both the techniques was found to be optimal from clinical point of view, but slightly superiorin case of TD-3DCRT. Based on these results 3DCRT technique in left breast cancer provides slightly more advantage.

   P-47: Hybrid VMAT Technique for Post-Mastectomy Chest Wall Irradiation: A Dosimetric Comparison Among Different Hybrid VMAT Plans. Top

K. Balaji1,2, S. BalajiSubramanian1, T. Moorthi1, K. Sathiya1 C. AnuRadha2, V. Ramasubramanian2

1Department of Radiation Oncology, Gleneagles Global Hospitals, Chennai, 2School of Advanced Sciences, VIT University, Vellore, Tamil Nadu, India. E-mail: [email protected]

Introduction: Hybrid Volumetric Modulated Arc Therapy (H-VMAT) is an innovative technique which uses conventional 3-Dimensional Conformal Radiotherapy (3DCRT) and VMAT. Several researchers have been compared hybrid IMRT/VMAT techniques with conventional 3DCRT, IMRT and VMAT techniques and reported the benefit of hybrid plans over conventional plans. Studies using H-VMAT in post-mastectomy setting are sparse. Majority of the published article favored VMAT technique over IMRT for chest wall irradiation.

Objective: In the present study, we used three different designs of VMAT for breast cancer patients to determine the optimal H-VMAT plan.

Materials and Methods: CT scan data of 10 post-mastectomy breast cancer patients (median age of 55 years) who received adjuvant radiotherapy were used for this study. Planning target volume (PTV) include chest wall and supraclavicular nodes (CW+SCL). The prescription dose was 50 Gy in 25 fractions (2Gy/fraction). The dose proportion of 3DCRT and VMAT used for hybrid plan was 80/20 percentage of prescribed dose. The isocenter was placed at CW and SCL junction. The 3DCRT plan consisted of two open tangential with half beam blocked fields for CW and one anterior oblique half beam blocked field for SCL. Three different VMAT designs include single partial arc (1A), two partial arcs (2A) and two tangential arcs (TA) were created. During VMAT optimization, the 3DCRT plan was kept as the base dose plan. All Plans were compared using various PTV dosimetric variables and Organs at Risk (OAR's) dose statistics.

Results and Discussions: The mean and standard deviation (SD) values of PTV coverage (D95%), conformity and homogeneity showed significant differences among all compared plans with p values 0.0006, 0.002 and 0.0002 respectively. Published clinical studies have cautioned about the potential risk for lung and cardiac injury even at low doses. The lung and heart low dose (V5Gy) results showed significant differences (Lung V5Gy: 53.79+1.59 Vs. 49.83+3.59, p=0.005 and heart V5Gy: 24.28+8.44 Vs. 28.06+3.14, p=0.034 for 2A Vs. TA H-VMAT plans respectively). All other OAR's mean doses were comparable. Significant difference in MU (p<0.0001) and treatment time (p<0.0001) were observed among all compared plans. The 2A H-VMAT achieved better PTV coverage, conformity, homogeneity and sparing of heart at V5Gy and V40Gy. The results of present study suggest that 2 Arcs H-VMAT plan is superior.

   P-48: Dosimetric Evaluation of VMAT with FF and FFF Photon Beam for Localised CA Prostate Top

Sarath S. Nair, G. C. Srinidhi, B. Ramya, Jyothi Nagesh, C. Shambavi1, Shreekripa1, Krishna Sharan

Department of Radiotherapy and Oncology, KMC, Manipal University, 1School of Allied Health Science, Manipal University, Manipal, Karnataka, India. E-mail: [email protected]

Introduction: Prostate cancer is the most common cancer in men, accounting for over one-fifth of male cancer diagnoses, Various radiotherapy techniques are used for treating prostate cancer have been considered effective treatment options. Especially for elderly patients and those unfit for surgery, VMAT improved delivery time and thus produced a highly conformal and accurate dose delivery when compared to intensity-modulated radiotherapy (IMRT). Recently, a new linear accelerator (linac) called ELEKTA HD versa with flattening filter-free (FFF) beams was introduced into our clinical operation. The benefits of removing the flattening filter is fast delivery time because of the high dose rates, and reduction of the head scatter and leakage, which leads to reduced exposure of normal tissue outside the target field. This study is to evaluate and compare the plan quality and efficacy of flattened and flattening-filter-free (FFF) photon beams in external beam RT for high-risk prostate cancer patients. Hereby we try to elucidate the difference in plan quality and treatment delivery time compared to flattening filter beams.

Materials and Methods: Eight patients for ca prostate are selected and planned. Using CT and MRI images all contours are drawn. Planning was done in monoco by using two full arcs with 6MV, 10MV flattened, and FFF photon beams. The prescribed dose was 72 Gy in 40 fractions for the planning target volume (prostate PTV), All plans were optimized using the same objectives and constraints in MONACO 5.11 planning system. Plans were then evaluated for PTV coverage, OAR. The number of monitor units and the treatment delivery times were also compared. For all cases, the objective of the planning was to cover at least 95% of the PTV with 95% of the prescribed dose (V95%≥95%).

We compared the cumulative dose-volume histograms (DVHs) and technical parameters for all cases. We also measured the mean, maximum, and minimum doses for the PTV. For the target coverage, V95% for PTV (i.e., the volume of PTV receiving more than 95% of the prescribed dose) several quality parameters were analyzed for the plans. The homogeneity index (HI) of the PTV was defined as (D5%)/D98%), where D2% is the maximum dose. The Set of segmentation parameters used in planning included 3 mm grid size, maximum control point of 180, 0.5 cm minimum segment width and Monte Carlo photon algorithm.

Results and Discussion: There was no significant difference in the PTV dose coverage using all energies compared. The conformity index for all plan are ≥0.78. Homogenity index is found ≤1.2, V95% is ≥98%. It is found that the treatment plan quality there is not much changes, Superior plans were obtained using 10 MV beams in terms of mean and minimum OAR doses, even though this difference was negligible. Mean of bladder and rectum is ≤43Gy and 51Gy. While the treatment delivery time of volumetric modulated arc therapy (VMAT) is considerably shorter using FFF beams, even though the beam MU is more. MU ranges from 490-1047. Sparing for the bladder and rectum was slightly better with the 10 MV FF and FFF plans than with the 6 MV FF and FFF plans, but the difference was negligible. Follow-up studies are needed to confirm the clinical outcome and toxicity of prostate using 6, 10 Mv FF and FFF beams in clinical use.

   P-49: Evaluation of Rapid Arc Plan with Anisotropic Analytical Algorithm and Acuros XB Dose Calculation Algorithm for Head and Neck Cancers: Our Experience Top

K. Janish, Reshma Bhaskaran, R. D. Praveen Kumar, B. Aswathi, Sandeep Madhavan, T. Ajaya Kumar

Department of Radiotherapy, Govt. Medical College, Kozhikode, Kerala, India. E-mail: [email protected]

Introduction and Aim: IMRT and RapidArc (RA) are the most common treatment techniques used in Radiotherapy now-a- days. The selection of the technique is in general the discretion of the people involved in treatment. Photon dose calculation algorithms in treatment planning system could affect the accuracy of dose delivery when tissue heterogeneity is involved along the path of the beam. Analytical anisotropic algorithm (AAA) is one of the widely tested and validated dose calculation algorithms in external beam photon radiation therapy. Recently, Acuros XB (AXB) was made available for photon dose calculations, and several studies have demonstrated better dose prediction accuracy of the AXB over AAA. This work aims to evaluate the Rapid Arc treatment plans for Head and Neck cancers with AAA and ABX dose calculation algorithms using the various plan comparison tools.

Materials and Methods: The study was done using Varian Eclipse (Ver.11) treatment planning system. 10 patients were selected. RA plans were done with two full arcs with 6MV and a dose rate of 600cGy/min for AAA and AXB. 2.5 mm grid size was used for both the calculations. The plans were optimized to get a minimum of 98% and maximum not more than 107% of prescribed dose to PTV. Both the plans were evaluated with DVH using tools like D2Gy (Dose received by 2% of PTV volume), D98Gy (Dose received by 98% of PTV volume), D95 Gy (Dose received by 95% of PTV volume), Dmean Gy (Mean dose for PTV), CI (Volume of PTV receiving 98% of dose/Volume of PTV), HI (D2-D98)/DPTV).

Results and Discussion: Comparing the plans we see that D98 Gy for AAA is 6497.9 ± 76.9 Gy and for ABX is 6394.7 ± 98.2 Gy. D2Gy for AAA is 6498.1 ± 60.8 Gy and for ABX is 6919.4 ± 81.3 Gy. Dmean Gy for AAA is 6769.3 ± 48.1 Gy and for ABX is 6723.8 ± 55.7 Gy. Conformity Index, CI for AAA is 0.92 ± 0.05 and for ABX is 0.86 ± 0.10. Homogeneity Index (HI) for AAA is 0.10 ± 0.02 and for ABX is 0.11 ± 0.02. One of the biggest advantages with regard to the plan calculation with AXB is that the dose calculation time is significantly reduced as compared to AAA. This is very helpful in departments like ours where the patient load is very high.

From the results we see that the plans generated using AAA calculation algorithms have better conformity index. The homogeneity index is same for both the calculation algorithms. Even though these factors are same the most important parameter in the radiotherapy treatment planning is the accuracy of the treatment delivery. Hence the doses were physically verified using an indigenously developed phantom. Since head and neck regions involve several inhomogeneity we found that the plans calculated using AXB were in better agreement with the physically verified doses.

   P-50: Dosimetric and Radiobiological Analysis for Prostate Cancer on Grid Size and Dose Calculation Algorithm Top

Kyeong-Hyeon Kim, Sang-Won Kang, Jin-Beom Chung1, Keun-Yong Eom1, Yong-Jin Kim, Tae Suk Suh

1Department of Biomedical Engineering, College of Medicine, Research Institute of Biomedical Engineering, The Catholic University of Korea, Seoul, 2Department of Radiation Oncology, Seoul National University Bundang Hospital, Seongnam, Korea. E-mail: [email protected]

In this study, we evaluated the dosimetric and biological impact on volumetric modulated arc therapy (VMAT) plan according to the dose calculation algorithm and the dose grid size in prostate cancer patients. The VMAT plans were exported in different dose grid and algorithm case, and dose calculation were implemented. By using Acuros XB (AXB), 1 mm, 2 mm, and 3 mm dose grid size were applied, and 1 mm, 3 mm 5 mm dose grid size were applied in AAA. Dosimetric parameter such as D2%, V95%, the homogeneity index (HI), conformity index (CI), and conformal number (CN) were calculated, and tumor control probability (TCP) and normal tissue complication probability (NTCP) of bladder, rectum, and femoral head were calculated for the radiobiological impact evaluation. In AAA algorithm case, the dosimetric parameter and TCP to planning target volume (PTV) were decreased with increasing dose grid size. As dose grid size was increased, the dosimetric parameter and TCP of AXB case were increased in the contrary with AAA. Average HI, CI, and CN showed worst value in AAA and 5 mm grid size, and were 0.13, 0.93, and 0.89 respectively. NTCPs of bladder, femoral head in all case were under 0%. NTCPs of rectum were 11.76 – 1.51%, and showed relatively large value in large PTV volume. Similarly with TCP, NTCP of rectum were increased with increasing dose grid in AXB, and decreasing dose grid in AAA. Calculation time of AXB were generally longer than that of AAA, and time difference between two algorithm were increase as dose grid size were decreased. As dose grid size were increased, dosimetric and biological impact of AXB and AAA algorithm showed different tendency, and calculation time increase according to dose grid size were different.

   P-51: Assessment of Volumetric Modulated Arc Therapy Optimization Strategy for Hypopharyngeal Carcinoma Top

N. Singh, S. Ahamed1

Department of Radiotherapy, King George's Medical University, Lucknow, Uttar Pradesh, 1Department of Radiotherapy, Basavatarakam Indo-American Cancer Hospital and Research Institute, Hyderabad, Telangana, India. E-mail: [email protected]

Introduction: The progressive resolution optimizer (PRO) of RapidArc volumetric modulated arc therapy (VMAT) generates varying field apertures alongside dose rate and gantry speed variations to arrive at variable MU per degree. MU objective tool available in Eclipse plan optimization environment controls monitor units and thus influences PRO.

Objective: To quantify relative merit of MU deprived plans against freely optimized plans in terms of plan quality and report changes induced by progressive resolution optimizer algorithm (PRO3) to the dynamic parameters of RapidArc.

Materials and Methods: Ten cases of carcinoma Hypopharynx were retrospectively planned in three sequential phases offering complex to simple combinations of target-critical structures. Each of the three clinical plans (baseline plans) was generated without using MU objective tool. Three plan replicas of baseline plans for each phase were reoptimized using the same tool intending to reduce MUs by 20%, 35%, and 50%. Intermediate dose feature along with MU tool was utilized to proceed with the baseline optimization for retaining a similar dose distribution but with lesser MU. This strategy helped to understand the changes made to baseline plans without starting a new loop which might produce but a different solution. Plan merit was quantified as an overall quality index, determined from individual dosimetric indices obtained from DVH for target and OARs separately. In addition to whole body integral dose, dose volume spread was also assessed at various dose levels in the entire patient and in CT sections containing target structures. Significant differences from plan sum comparisons were reported. To analyze the changes induced by PRO3 while reducing MUs, mean values of leaf aperture, CP area, and absolute delta dose rate variation were derived in addition to MU per Gy and dose rate. All plans were appraised for changes induced in RapidArc dynamic parameters and pre-treatment quality assurance (QA).

Results and Discussion: With increasing MU reduction strength (MURS), MU/Gy values reduced, for all phases with an overall range of 8.6–34.7%; mean dose rate decreased among plans of each phase, phase3 plans recorded greater reductions. MURS20% showed good trade-off between MUs and plan quality, yielding equivalent and acceptable plans. Dose-volume spread below 5 Gy was higher for baseline plans while lower between 20 and 35 Gy owing to the dose sculpting ability over the MU deprived plans. Integral dose was lower for MURS0%, not exceeding 1.0%, compared against restrained plans. Mean leaf aperture and control point areas increased systematically, correlated negatively with increasing MURS, resulting in increased effective field size. Absolute delta dose rate variations were least for MURS0%. MU deprived plans exhibited GAI (>93%), better than MURS0% plans, due to reduced modulation complexity.

Conclusions: In this retrospective study, a methodical approach was established to make use of MU objective tool in conjunction with intermediate dose feature and its influence on VMAT dynamic parameters. MU objective tool has a marked influence on the PRO3 algorithm in reducing MUs irrespective of the complexity or size of the target volumes and proximity of OARs. Baseline plans are superior to MU restrained plans. However, MURS20% offers equivalent and acceptable plan quality with mileage of MUs, improved GAI for complex cases. MU tool may be adopted to tailor treatment plans using PRO3.

   P-52: LEft breast Irradiation with Tomotherapy: TomoDirect or TomoHelical - A Dosimetric analysis Top

Jerrin Amalraj, S. Rajesh, A. Pichandi, A. Dinesh

Department of Radiation Oncology, Central Physics Division, HCG Enterprises Ltd., Bengaluru, Karnataka, India. E-mail: [email protected]

Introduction: Adjuvant whole-breast external beam radiation therapy is an integral part of the current standard multimodality approach for early stage breast cancer. Radiotherapy planning for breast cancer patients is technicallychallenging because of varying size and shape of the breast as well as setup reproducibility and respiratory motion. Different techniques have been adopted for radiotherapy of left breast say 3D conformal tangential fields with wedge filters, field in field techniques, intensity modulated radiotherapy (IMRT), volumetric arc etc. Over the years, Tomotherapy system was able to deliver highly conformal IMRT plans within helical geometry under image guidance for left breast irradiation. A platform upgrade named TomoDirect® in Tomotherapy empowered users to plan and deliver radiation at user defined static gantry angleswith the couch moving at a constant rate past a fixed binary multileaf collimator. This study investigates how TomoDirect (TD) is equitable with TomoHelical (TH) delivery for the radiotherapy of left breast.

Objective: The aim of this study is to investigate TomoDirect (TD) plans in terms of dosimetric outcomes of target coverage and organ at risk (OAR) sparing and to compare with TomoHelical (TH) counterpart for left breast irradiation.

Materials and Methods: Study population consist of 10 patients presented with carcinoma left breast submitted to whole breast radiotherapy. Retrospective plans are constructed with both TD and TH approach to a prescription dose of 50 Gyto the breast PTV with session dose of 200cGy. Planning were done with Tomotherapy planning station with VoLo Optimization. Clinically acceptable plans were generated for both techniques and compared. Dosimetric parameters such as D98%, V105%, V110% for target volume and volume of organs receiving specific doses; say V5Gy, V10Gy, V20Gy, V30Gy and their mean doses were compared.

Results and Discussion: Plan quality were quantified with respect to target volume coverage, target homogeneity, low doses to OARs. Mean Dose to 98% Target volume for TD and TH are 48.6Gy ± 86 and 48.8Gy ± 87 respectively. TH plans showed slightly better PTV coverage and homogeneity compared to TD. Mean low dose volume V5Gy to ipsi-lateral lung, Heart, contra-lateral breast and unspecified tissues of body were 48% ± 8.7, 25.5% ± 0.9, 1.72% ± 1.4, 13% ± 4 and 74.2% ± 16, 38% ± 17, 35% ± 16, 24% ± 10 for TD and THrespectively. It is observed that low dose regions to lungs, heart and unspecified tissue of the body were significantly lesser with TD compared to TH. However, mean lung and heart dose (TD: 1287Gy ± 41.6 and 684Gy ± 29; TH:1249Gy ± 21.4 and 589Gy ± 20) were lesser with TH compared to TD. Scoring of TD over TH could be based on the central lung distance (CLD) and maximum heart distance (MHD). It is observed that for plans with average CLD, MHD less than 1.7 cm and 2.5 cm respectively, TD scores over TH for overall OARs sparing and vice versa.

Conclusion: The choice of technique whether TD or TH is solely patient specific based on planning target volume delineation and the proximity of lungs and heart irradiation volume. CLD and MHD are useful parameters to decide the choice the technique to be used for planning left breast radiotherapy.

   P-53: Dosimetric Comparison of Four Different Intensity Modulated Radiotherapy Techniques in Carcinoma Oesophagus Top

Soumya N M, Ranjitha K H, Resmi K B, Silpa Ajay Kumar

Department of Radiation Oncology, Malabar Cancer Centre, Thalassery, Kerala, India. E-mail: [email protected]

Introduction: Radiation therapy is a clinical modality dealing with use of ionizing radiations in the treatment of patients. The aim of radiation therapy is to precisely deliver measured dose of radiation to a defined tumour volume with as minimal damage as possible to surrounding normal tissue. Linear accelerator can be used for the effective treatment delivery. Modern Linacs have different radiation treatment technique like Three Dimensional conformal radiation therapy 3DCRT, intensity modulated radiation therapy IMRT, volumetric modulated arc therapy VMAT (/RAPID ARC), Image guided radiation therapy IGRT, Stereotactic radiotherapy etc. Treatment planning in the system allows to achieve the goal of radiotherapy.

Aim: The aim of this study is to find out the best treatment technique in the case of oesophageal carcinoma.

Objective: In radiotherapy there are different types of treatment technique and beam orientations in treating oesophageal carcinoma. So it is very important to find out the best treatment technique in terms of target coverage and sparing of critical organs.

Materials and Methodology: 14 patients who were already treated for oesophageal carcinoma with a technique using a combination of volumetric modulated arc therapy (VMAT) and three dimensional conformal radiation therapy were considered for the study. All those cases were re-planned with VMAT, a 4 field intensity modulated radiation therapy (IMRT) technique and with a 9 field IMRT technique. The treatment plans were evaluated and compared to find out which plan is best among the four in terms of target dose coverage and sparing of organs at risk. Factors like dose received by 95% of the planning target volume, Homogeneity index, Volume of lung receiving dose of 20Gy (V20), V30, V10, V5, mean dose of lung, mean dose of heart and maximum dose to spinal cord were evaluated and compared. The treatment planning system Eclipse10.0 was used for creating plans.

Results and Discussion: All plans meet the target dose prescription requirements. The combined 3DCRT + VMAT technique provides good target coverage and homogeneity. The lung V20 is the least in this technique. The V30 of lung is less than 20%. The V10 and V5 values of lung are also least in this. Compared to other techniques, spinal cord dose is high. But still it can limit within the tolerance. In VMAT alone plans, the V20 values exceeds the limit of 30%. In 4 field IMRT and 9 field IMRT all OAR's can achieve with compromised target coverage. If we try to increase the coverage all the OAR's will exceed the tolerance doses.

   P-54: Dosimetric Comparison of IMRT Versus 3DCRT for Post Mastectomy Chest Wall Irradiation Top

Kartick Rastogi

Department of Radiation Oncology, Sawai Man Singh Medical College and Attached Group of Hospitals, Jaipur, Rajasthan, India. E-mail: [email protected]

Introduction: Breast cancer is the most common cancer in females. In India, especially Rajasthan, most of the patients present with Locally Advanced Breast Cancer (LABC) so mastectomy is performed more often than Breast Conservative Surgery (BCS). Most of these patients require Post Mastectomy Radiotherapy (PMRT) to decrease locoregional recurrence. 3-dimensional conformal therapy (3DCRT) is widely employed radiation therapy technique, but there is still need to minimize the doses to organ at risk (OAR). A few clinical studies have discussed the role of intensity modulated radiation therapy (IMRT) to address this issue.

Objectives: To compare the dose distribution of 3DCRT and IMRT in post mastectomy left sided female breast cancer patients.

Materials and Methods: 110 post mastectomy left sided breast cancer patients were randomised for adjuvant chest wall irradiation in 3DCRT group (n=67) and IMRT group (n=43). All patients were treated on linear accelerator with 50Gy in 25 fractions. The mean doses of lung and heart, percentage volume of ipsilateral lung receiving 20Gy (V20) and heart receiving 25Gy (V25) were extracted from dose-volume histograms (DVHs) and compared between two groups.

Results: The target coverage was achieved with 90% prescription to the 95% volume of the PTV. On average, the V20Gy of ipsilateral lung was significantly higher in 3DCRT than in IMRT group (30.9% and 22.4% resp., p< 0.05) but V5 was significantly lower in 3DCRT than in IMRT group (51% vs. 64% resp., p<0.05). Similarly, the average V25Gy of heart was significantly higher in 3DCRT than in IMRT group (8.7% vs. 4.3% resp., p<0.05).

Discussion: IMRT for the chest wall irradiation of postmastectomy left sided breast cancer patients offers the potential to significantly reduce the high dose-volume of the ipsilateral lung and heart compared to 3D-CRT.

   P-55: Analysis of Photon Beam Skin Dose for Physical and Enhanced Dynamic Wedges for Different Field Sizes for 6 MV and 15 MV Photons Top

Titiksha Vasudeva1,2, Baljeet Seniwal1,2, Ranjit Singh2, Arun S. Oinam2

1Centre for Medical Physics, Panjab University, 2Department of Radiotherapy and Oncology PGIMER, Chandigarh, India. E-mail: [email protected]

The introduction of high energy linear accelerator in radiotherapy allows treatment of deep seated tumors with better dose homogeneity and conformity. The greater penetration of high energy mega-voltage X-rays results in reduction of doses to the skin surface. Apart from primary radiation, electron scattered from collimator head and patient's body contributes significantly to the skin dose. The patient scattered depends upon area of the irradiation and the contribution from collimator depend upon it's distance from the patient's surface. The commercially available treatment planning algorithm (Pencil beam algorithm (PBC), anisotropic analytical algorithm (AAA)) shows a significant variation at the surface interface and the dose gradient region.

Various beam modifying devices (e.g., wedges, shielding block, Multi leaf collimator (MLCs) etc.) are used in treatment planning system to adequately cover the target volume with the prescribed dose without exceeding the doses to the normal structures. The wedge filters are commonly used as a tissue compensator and it results in tilt of iso-dose curve toward thicker end. Physical and Enhanced dynamic wedges (EDW) are the two main class of wedge filters routinely used in radiotherapy. The skin dose drastically changes with the introduction of these two classes of wedge filters.

The aim of the present study is to evaluate skin doses for 6 MeV and 15 MeV photon beams at different field sizes (5 × 5, 10 × 10, 15 × 15, 20 × 20, and 40 × 40 cm2) and for different wedge angle (15°, 30°, 45° and 60°). The experiment was performed on Clinac DHX dual energy linear Accelerator (Varian Oncology Systems, Palo Alto, CA). The solid water phantom RW3 (dimension 30 × 30 cm2, 0.1-1 cm thickness range) (density 1.09 g/cc), parallel-plate ion chamber (PPC-40 (IBA (S/N-913) and supermax (Standard Imaging (S/N-P09133, +300 V polarizing potential) electrometer were used for the measurement. The source to surface distance (SSD) was 100 cm and all measurements were carried out upto a depth of 4 cm with backscattered thickness of 15 cm. The percentage depth dose data were measured for all wedge angles and field sizes. The meter readings (electrometer) were recorded and normalized with the meter reading obtained at the depth of maximum dose. The percentage depth dose at surface (PDD0) increases with the increase in field size, both for enhanced dynamic (EDW) and physical wedged (PW). The surface doses are slightly higher for EDW as that for same angled physical wedge.

   P-56: Utility of Manual Selection of Jaw Placement and Collimator Rotation in the Rapid-Arc Planning for Large Volumes with HDMLC Top

R. C. Jaon bos, Gopinath Menon, Jayadevan Pattaloor, Jose Paul, Arunlal, Jino Joseph, Sreedev, Nizar

Department of Radiation Oncology, Aster Medcity, Kochi, Kerala, India. E-mail: [email protected]

Introduction: Rapid Arc as it's known for, provides with increased degrees of freedom utilising entire span of Gantry and Multi-leaf Collimator movement and their speed along with dose rate modulation. While using High Definition MLC for extended target volumes, regions stretching beyond the limited width of HDMLC bank gets compromised in terms of degrees of freedom that Rapid-Arc provides resulting in in-homogeneous dose distribution and increased spillage of prescription and lower doses.

Objective: Utility of manual selection of jaw placement and collimator rotation in the Rapid-Arc planning with HDMLC for large volumes is studied. A technique of manual intervention in the planning process by limiting jaws and appropriately choosing collimator rotation to effectively increase the degrees of freedom that produces homogeneous and conformal distribution is presented.

Materials and Methods: High Definition MLC with 120 leaves by Varian Medical Systems on True-beam platform with Eclipse planning system were used for all Rapid-Arc planning. Maximum width of this HDMLC bank is 22 cm and region of targets extending beyond this limit suffers the aforementioned problem. Routinely 1 to 3 arcs with optimum collimator rotation of 30 and 330 suffices to achieve a clinically acceptable distribution.

Additional arc with feasible collimator rotation that make the leaves to travel along the maximum dimension of the target exploiting maximum over-travel distance of 15 cm works very well but has its own drawbacks when employed for large volumes as following. (1) Leaves have to traverse more distance and more number of them are pushed to travel at their maximum speed of 2.5 cm/s. Since leaf position uncertainty is found to be more with increase in their speed which in turn results in poor gamma in quality assurance. (2) Leaves modulating over the entire length of volume at a time diminishes the degrees of freedom of leaf positioning, i.e. constraints met at particular region of volume takes away freedom of achieving clinical goal in another region.

The methodology used for solution to this problem is to have the additional arc limited to modulate over the particular in-homogeneous region of target volume. This is achieved by limiting jaws to the particular region along with a collimator rotation that makes leaves travel along the longer dimension of target before proceeding to optimization. If needed, this additional arc can be split into two different arcs independently modulating over such different regions e.g. cranial and caudal extent of PTV with the collimator rotation 90 or lateral aspects of PTV with near zero collimator rotation one for left lateral and the other for right lateral.

With this method the connectedness existing among the DoF subsets of all arcs used for modulation is minimised and makes them mutually more exclusive.

Results and Discussion: “The jaw arrangement used for a pelvic volume with inguinal nodes, and the resulting distribution using this method is shown in [Figure 1]”, and the resulting distribution using this method is shown in [Figure 2]. Distribution obtained with this method is superior in terms of conformity and spillage of lower doses as well.
Figure 1: A two IC plan converted to single IC plan by splitting the additional arc into 2 arcs confined to superior and inferior aspect of PTV respectively with collimator rotation 90 and the resultant distribution obtained

Click here to view
Figure 2: The single IC plan sparing normal tissue of 80% of prescription dose in split regions

Click here to view

Jaw arrangement used for a volume in the lungs extending cranially into neck region and resulting distribution is shown in [Figure 2]. The third arc used in this case produces better sparing of medial structures in its confined region.

Utilizing analogy of DoF with connectedness in topology could yield better solutions to optimization problem in near future.

   P-57: Systematic and Dosimetric Evaluation of Static and Dynamic Conformal Radiotherapy Plans Using Different Optimization Parameters Top

Radhika Jain, Rose kamal1, Pankaj Kumar, Sajal Kakkar, Varinder Singh Chabbra

Department of Radiation Oncology, Max Super Speciality Hospital, Mohali, Punjab, 1Department of Radiation Oncology, Institute of Liver and Biliary Sciences, New Delhi, India. E-mail: [email protected]

Introduction: The development of advanced techniques of Radiotherapy viz. IMRT, IGRT, SBRT, Gating techniques etc. has led to very precise delivery of dose to tumour, sparing surrounding normal tissues, increasing the efficacy of treatment. Accurate dose calculation in TPS is the key factor to achieve the aim. The grid size of dose calculation cube determines the resolution of dose calculation and hence accuracy at the boundaries of adjacent structures of tumours.

Aim and Objective: The aim of the study is to determine the site specific optimum grid size resolution and optimal parameters for dose calculation in TPS i.e. minimum segment widths, number of control points and to incorporate it in clinical protocols.

Materials and Methods: Monaco (5.11) treatment planning system is used to generate the plans for each site with different grid sizes. Plan evaluation is done on the basis of standard evaluation tools i.e. slice by slice and DVH comparison etc. A Medical Linear Accelerator Elekta Synergy Platform equipped with 80 MLC is used for dose delivery using VMAT and IMRT technique. IMATRIXX is used for verification of delivered dose using gamma evaluation method.15 patients of Head and neck, prostrate, Brain and cervix, and Breast evaluated and 3D Gamma analysis of each plan is done using IMRT phantom.

Results: There were no significant differences for dose volume histogram (DVH) values between grid sizes. The calculation time was significantly higher for grid size 1.0 - 2.5 mm. The Monitor units varied by 5-10%, for smaller grid size the MU was less. A 4-mm grid size changed the dose variation by up to 3–4% (50 cGy) for the heart and the spinal cord, while a 3-mm grid size produced a dose difference of <1% (12 cGy) in all tested OARs. The segment width showed comparative variation. As we change no of control points the number of MU is increased and quality by increasing number of control points but treatment delivery and calculation time increases. Gamma evaluation of calculated and measured dose distributions is within tolerance (3% and 3 mm).

Conclusion: Grid size of Dose calculation cube, segment width, and no of control points is an important factor for accurate dose calculation depending upon the site and corresponding surrounding structures adjacent of tumour for different sites. The optimal selection and combination of these three parameters effects the plan quality.

   P-58: Effect of Multicriterial Optimisation Option in Monaco V5.0 TPS On Serial and Parallel Organs Top

Rahul Phansekar, S. Divya, Vipul Patel1, Hemendra Mod1

Departments of Medical Physics and 1Radiation Oncology Aaruni Hospital Pvt. Ltd., Rajkot, Gujarat, India. E-mail: [email protected]

Introduction: The basic planning challenge of radiotherapy is to handle the trade-offs between achieving the required tumour dose meanwhile not overdos-ing the surrounding healthy organs. A multicri-terial optimisation (MCO) allows the treatment planners to explore and understand these trade-offs thus providing a means to select the best plan for each patient.

Objectives: This study is to investigate the effect of multic-riterial optimisation in MonacoV5.0 treatment planning system (TPS) on Serial and Parallel organs.

Materials and Methods: Our department is equipped with Elekta Com-pact 6MV Linac with 80 leaves MLC (MLCi2), Monaco V5.0 TPS. Fifteen IMRT cases were selected for this study. Five head and neck cas-es with bilateral neck nodes and 5 with unilater-al neck nodes; similarly 5 thoracic and abdo-minal cases with no GTV involved are selected. For each case we made 3 IMRT plans. First plan without applying MCO to any organ; second by applying MCO only to serial organs and in third plan applying MCO only to parallel organs. Dose calculations were performed by keeping same constraints for PTV and OARs in all cases. For all plans, dose was calculated with Monte Carlo algorithm with dose calculation grid of 3 mm. We analyzed the dose volume his-tograms of all three plans generated for each patient. The Parameters used for comparison of the plans are Total Volume of PTV (TV), Vo-lume of the PTV covered by 95% isodose line (VRI), which is our reference isodose line (RI), Maximum dose to the PTV (Dmax), Minimum dose to the PTV (Dmin), maximum dose to the Serial organs and mean dose to the parallel or-gans. From above obtained parameters Confor-mity Index (CI), Quality of coverage (Qcov) and Homogeneity index (HI) were calculated as proposed by Radiation Therapy Oncology Group (RTOG).

Conformity Index RTOG = VRI (95%)/TV (1)

Results and Discussion: It has been observed that there is no significant difference in conformity index, quality of cov-erage and homogeneity index for all three plans generated for each patient as depicted in [Table 1],[Table 2],[Table 3],[Table 4],[Table 5],[Table 6].. We have no-ticed that the spinal cord doses are reduced significantly with MCO option selected. In head and neck cases with unilateral neck node PTV, the maximum reduction in spinal cord dose was (3925.9cGy to 3049.3cGy) and average reduc-tion was (4031.18cGy to 3514.58cGy). In head and neck cases with bilateral neck node PTV, the maximum reduction in spinal cord dose was (4329.7cGy to 3201.6cGy) (1128.1cGy) and average reduction was (4409.3cGy to 3589.12cGy) with MCO. In head and neck cases with unilateral neck node PTV the maxi-mum reduction in mean dose to contralateral parotid dose was reduced (1404.6cGy to 867.6cGy) and average reduction was (1183.8cGy to 755.7cGy) with MCO. In head and neck cases with bilateral neck node PTV the maximum reduction in mean dose to left and right parotid dose was (2579.9.cGy to 1896.4.cGy) and (2271.8.cGy to1653.8cGy) and average reduction was (2477.0cGy to 2252cGy) and 2395cGy to 2078.8cGy) respectively. In case of thorax and abdominal cases the maxi-mum reduction in spine dose was (3649.4 cGy to 1637.5cGy) and average reduction was (3696.2cGy to 2814.4cGy) with MCO. The maximum reduction in mean dose to left and right lungs dose was (1219.0cGy to 1016.0cGy) and (1283.5cGy to 1122.4cGy). Average mean dose reduction to both lungs was (1180.8cGy to 1049cGy) and (1271.6cGy to 1162.6cGy) with MCO. The maximum reduction in mean liver dose was (1422.7cGy to 1018.3cGy) and aver-age reduction was (1118.58cGy to 934.5cGy).
Table 1: Head and neck intensity modulated radiation therapy cases with unilateral planning target volume

Click here to view
Table 2: Head and neck intensity modulated radiation therapy cases with bilateral planning target volume

Click here to view
Table 3: Abdominal and thorax intensity modulated radiation therapy cases

Click here to view
Table 4: Conformity index

Click here to view
Table 5: Quality of coverage

Click here to view
Table 6: Homoginity index

Click here to view

From above study we can say that muliticriterial optimisation tool in Elekta Monaco TPS effec-tively helps to reduce the doses to critical or-gans in IMRT planning.

   P-59: 3DCRT Breast Irradiation – Organ at Risk Doses from Reduced Target Volume Margins Top

D. Basaula1,2, N. P. Freeman1, A. Quinn3, A. Walker2, 4, 5, V. Batumalai2, 4, 6, S. Kumar2, 4, 6, G. P. Delaney2, 3, 6, L. Holloway2, 3, 5, 6, 7

1Department of Medical Physics and Radiation Engineering, The Canberra Hospital, Garran, 5Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 2Ingham Institute of Applied Medical Research, 3Northern Sydney Cancer Therapy Centre, Royal North Shore Hospital, 4Liverpool and Macarthur Cancer Therapy Centres, 6University of New South Wales, 7Institute of Medical Physics, University of Sydney, Sydney, Australia. E-mail: [email protected]

Introduction: Three dimensional conformal breast radiotherapy (3DCBRT) results in radiation dose to organs at risk (OARs) such as heart, lung and contralateral breast. Radiation dose received to OARs during the course of breast radiotherapy has shown to be associated with increased risk of radiation induced health issues. Potentially, by reducing breast planning target volume (PTV) margin, OARs dose can be reduced.

Objective: This study investigates the effect of planning target volume (PTV) margin reduction for 3DCBRT in relation to dose received by organs at risk (OARs).

Materials and Methods Using ten retrospective patients computed tomography (CT) datasets, delineation of target volumes and OAR structure were made. For each patient, three different PTV were created by adding different margins (0 mm, 5 mm and 10 mm) to clinical target volume (CTV). Treatment plans were created for each PTV with a 3DCBRT field-in-field technique using the XiO version 4.64 treatment planning system (TPS). The compliance with the Radiation Therapy Oncology Group (RTOG) 1005 protocol requirements was followed. A prescription dose of 50 Gy in 25 fractions to the PTV was used to generate treatment plans. Each patient's dose volume histogram (DVH) data were extracted from treatment plans and used to evaluate the doses to OARs. Measurement of relative dose for comparison with treatment planning system calculated dose was performed in CIRS IMRT Thorax phantom.

Results and Discussion: By changing PTV margins from 10 mm to 0 mm, mean dose reduction of 31% (heart), 28% (lung) and 23% (contralateral breast) was obtained. Such reduction in dose would reduce the radiation induced health issues to OARs. However, careful consideration must be given to clinical implication of reduced PTV margins. Significant reduction in margin may cause inferior treatment outcomes.

   P-60: Traceability of Dose Between Treatment Planning System and Linear Accelarator for Various Treatment Modalities Top

Dince Francis, C. A. Shahan Shad, Daicy George, V. Ramya, P. Suresh Babu, S. Sowmya Narayanan

Vydehi Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, India. E-mail: [email protected]

Objectives: The goal of radiotherapy is to cure or locally control the disease while minimizing complications in normal tissues. The International Commission on Radiation Units and Measurements recommends that radiation dose has to be delivered within ±5% of the prescribed dose. Computerized Radiotherapy Treatment Planning Systems (RTPS) are used to get in-patient dose calculation using machine data. Precise dose delivery, both geometrically and dosimetrically is crucial for the successful outcome of the treatment. Thus, there is a need for rigorous dosimetry and quality controls in order to ensure precision and accuracy of dose estimation in treatment planning software. In this study, the traceability and reproducibility of planned dose between RTPS and Linear Accelerator for various treatment modalities is verified.

Materials and Methods: The equipments used for this study were Treatment Planning System (Eclipse, Version11.1, Varian Medical Systems & Monacco, Version5.1, Elekta Medical Systems), Medical Linear Accelerator (Clinac 2300C/D, Varian) able to deliver IMRT and VMAT with multi-leaf collimators and 4D CT Scanner (GE Medical Systems). The Dose calculation and delivery accuracy check was performed in homogeneous and non-homogeneous mediums for conformal static fields (3DCRT) as well as dynamic field techniques (IMRT, VMAT). The Mini water phantom was used for dose measurement in homogeneous medium whereas Lung phantom and CIRS phantom were used for the same in heterogeneous medium. The Pencil Beam Convolution (PBC), Anisotripic Analytical Algorithm (AAA) and Collapsed Cone Convolution (CCC) algorithms were used for dose calculation for 3DCRT plans whereas AAA was used for the same in IMRT and VMAT plans. The doses were calculated at different positions in the medium, i.e., at different densities within the phantom. The choice of detector (FC65G or CC13) for dose measurement was made according to the provision provided in the phantom. The plan delivery was performed with the aid of IGRT capabilities to account for any geometrical shift of the target. The TPS calculated dose and the measured dose were compared and deviation is noted. The QA on homogeneous phantom was performed on monthly basis and checked for its consistency. In addition, accuracy check of dose delivery is supplemented using the TLD capsule irradiation for 2 Gy at 10 cm depth for 10 x 10 cm2 field size for 100 cm SSD, for 6 and 15 MV energies.

Results and Discussion: The accuracy of dose delivery is within ±2% for simple field in homogeneous medium. For symmetric field technique, the accuracy of dose delivery lies within ±3% and for 3DCRT, IMRT and VMAT, the agreement was within ±5% for both algorithms in heterogeneous medium. The TLD response shows a difference of -0.5% and -1.3% for 6 and 15 MV respectively. The study over one year period ensures the acceptable quality of the RTPS, which is capable of delivering dose to the patient within an accuracy of ±5%. The dose delivery over the study period is found to be consistent.

Conclusion: The reproducibility and traceability of planned dose from TPS to the treatment unit was accurate. The quality and the functionality of the TPS is found to be within the accepted tolerances, which are mandatory to obtain the requisite clinical outcome with an optimal treatment delivery. This study enhances the level of confidence in the efficient treatment delivery.

   P-61: Cranio Spinal Irradiation Techniques: A Dosimetric Comparision of Helical Tomotherapy with Volumetric Modulated Arc Therapy Top

M. Sathiya Seelan1,2, R. Murali2, K. Tamilselvan1, G. Padma1, M. K. Revathy1, N. Arunai Nambi Raj2

1Department of Oncology, Apollo Cancer Hospital, Hyderabad, Telangana, 2School of Advanced Sciences, VIT University, Vellore, Tamil Nadu, India. E-mail: [email protected]

Objective: Cranio Spinal Irradiation (CSI) is a challenging procedure of treating various central nervous system malignancies. Large PTV size (includes whole Brain and Spinal Cord and overlying meninges) requires field matching due to technical limitations of conventional linear accelerators (LA), which cannot irradiate such volumes as a single isocentre treatment. Helical Tomotherapy (HT) could help to avoid these limitations as irradiation of long fields is possible without field matching. This study aims to assess the dosimetric comparision of treatment plans between HT and Volumetric Modulated Arc therapy (VMAT) of CSI.

Materials and Methods: CT datasets of Four (n=4) previously treated patients with medulloblastoma were used to generate VMAT plans in Eclipse V13.6 and HT plans in VoLO planning system V5.1.0.4. In both plans a total dose of 36Gy in 20 fractions with 2Gy per fraction was prescribed such that at least 98% of the volume of PTV received at least 95% of the prescription dose. Plans were compared using PTVs conformation number (CN), homogeneity index (HI), normal tissue mean dose statistics, body mean dose and treatment time.

Results and Discussion: HT plans showed better homogeneous dose distribution to PTV with a mean (SD) HI of 0.06 (0.006) vs. 0.10 (0.019) for VMAT plans. In terms of conformity VMAT plans showed marginally better CN with mean value of 0.83 vs. 0.76 for HT plans. Normal tissue mean dose statistics included the structures total lungs, total kidneys, heart, oesophagus, liver, thyroid, parotids, oral cavity showed 1.1-1.39 (mean, 1.25) times higher in VMAT plans compared to HT plans. Both the plans showed average body doses were same. HT plans showed mean beam on time 11 mins vs. 6.25 mins for VMAT plans. However, beam –on time is not necessarily representative of the total time the patient will spend in the treatment room, factors such as patient setup and imaging, shifting patients to different isocentres, gantry rotations must be considered to estimate the overall treatment time. Considering all such factors, in our institute the patient who underwent CSI treatment patient spent average of 30 mins and 25 mins for HT and VMAT respectively from setup to treatment delivery. In conclusion, radiation treatment planning and delivery of CSI with a homogeneous dose distribution remains one of the most challenging processes. HT for CSI is favourable in terms of PTV coverage, homogeneous dose distribution, conformity, OAR sparing. Overall HT is technically easier without any junction matching and dosimetrically superior than VMAT.

   P-62: Dosimetry Verification of Stereotactic Body Radiation Therapy for Hepatocellular Carcinoma Treatment Top

R. P. Srivastava, B. Katarzyna, S. Junius, K. Thevissen

Centre Hospitalier Mouscron, Mouscron, Belgium. E-mail: [email protected]

Purpose: A new radiotherapy technique, stereotactic body radiation therapy (SBRT) allows safe delivery of higher dose external beam radiotherapy to liver tumours and the focus of the treatment has shifted from palliative purposes to cure-oriented therapy. A dosimetric study was performed to evaluate the performance of stereotactic body radiation therapy with Rapid Arc on hepatocellular carcinoma.

Materials and Methods: Ten patients with unresectable HCC were enrolled in this study. The patients were calculated using the Eclipse planning system (version 11.0) with the 120-leaf multi-leaf collimator (MLC) (Varian Medical Systems). Dose prescription varied from 45 to 62.5 Gy to the Planning Target Volume of 80% prescribed dose in 3 to 10 fractions. A verification plan was created for portal dosimetry (PD) and PTW Octavius 4D phantom (Detector 1000 SRS). All plans were analysed using gamma-index with 3% dose tolerance and 3 mm (PD) and distance to agreement and 2%, 2 mm for Octavius 4D in relation to the treatment planning system.

Results: PD 95% and Octavius 4D phantom100 % confirmed a good agreement between the two distributions with high dose and conformed dose to the target and low dose to the organ at risk. All measurements passed with at least 95% of the measurements within gamma-criteria. SBRT allowed to achieve required target coverage as well as to keep within normal tissue dose/volume constraints. The presentation will include some practical and pitfalls.

   P-63: Tumor and Critical Organ'S Dose Arising from Different Radiotherapy Techniques Applied to Parotid Gland: A Comparison Between Calculated and Measured Dose Top

Mohammad Taghi Bahreyni Toossi, Hamid Gholamhosseinian, Atefeh Vejdani Noghreiyan1

1Medical Physics Research Center, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. E-mail: [email protected]

Introduction: Parotid gland tumors account for 3% of head and neck tumors. Adjuvant radiotherapy is suggested for reducing the risk of high grade parotid tumors.

Objectives: the aim of the present study was to compare patient's dose arising from different techniques applied to treat parotid gland tumors and suggest useful modification, to optimize organ's dose.

Materials and Methods: The dose of target volume and OARs of three usual parotid gland radiotherapy techniques were measured on Rando phantom by TLDs. Tech1: mixed beam of 6 MV photons and 10 MeV electrons technique (weighting=1:2). Tech2: Paired wedged 6 Photon beams, Tech3: Paired wedged 6 Photon beams using MLC. Then, measured doses were compared with corresponding values obtained from treatment planning calculations. Finally, the best technique was suggested with respect to tumor dose sufficiency and homogeneity, and organ at risks protection. Results and discussion: Tech2 and tech3, significantly improved the dose homogeneity in PTV (ΔD95% - 5% =2.31, 2.28, respectively). Tech3 was the most effective factor in dose reduction to tissues beyond the target volume. Tech1 kept the lowest dose to oral cavity (1.9 Gy). PTV received at least 95% of the prescribed dose in all techniques. Based on the TRS-430 protocol, 95% of the measured dose by TLD inner and outer of the field was in good agreement with the treatment planning system calculations, for three techniques. In the studied techniques, tech1 can be considered for protecting oral cavity and preventing xerostomia. Regarding target dose homogeneity, tech2 and tech3 were considered as the optimal techniques; moreover, in reduction dose to structures sticking to target volume, tech3 was selected. It is suggested that, whether during the treatment, three techniques are used instead of single technique, the critical structures surrounding are spared more efficiently, and the tumor volume receives sufficient and homogeneity dose.

   P-64: A Treatment Planning Study: Statistical Evaluation of Dynamic and Static IMRT Techniques Top

Kaur Amandeep, Sharma Ramita, Sachdeva Kanchan

Department of Radiotherapy, Sri Guru Ram Das Institute of Medical Sciences and Research, Amritsar, Punjab, India. E-mail: [email protected]

Introduction: Radiotherapy is one of the most common modalities used for the treatment of cancer in addition to surgery, chemotherapy and hormonal therapy. External beam radiotherapy directs high energy rays from outside the body to the tumor. Intensity modulated radiotherapy (IMRT) is a mode of delivering high precision conformal radiotherapy with computer- controlled Linear Accelerator having multi-leaf collimation (MLC) system. IMRT is usually delivered via two techniques viz. the static or step and shoot (SS) mode and the dynamic or sliding window (SW) mode of delivery. In the static mode IMRT the radiation beam is ON only when the MLCs are set to the discrete aperture shapes and are stationary at each sub-field. While in the dynamic IMRT delivery mode the beam remains ON as the leaves move to take shape for the next sub-field.

Objective: The purpose of our study was to evaluate the statistical differences between the treatment plans generated for head and neck and pelvis cases at our centre with both the static and sliding window technique.

Materials and Methods: In this study, five cases each for head & neck and pelvis were planned with 6MV on Elekta Monaco 5.0 Inverse Treatment Planning Software for IMRT utilizing Monte- Carlo algorithm. The cases were planned with both step and shoot and dynamic IMRT techniques keeping the optimization constraints same. Gamma analysis was applied to the plans with the Compass software version 3.1 to meet the 95% pass criterion at 3%/3 mm. The plans for each individual case with both techniques were evaluated in terms of Dose Volume Histogram parameters viz. Dmax , Dmean , D 95%, D 1% Uniformity index, Homogeneity index, Conformity index (at 95% isodose) and number of Monitor Units.

Results: On evaluation of plans, it was observed that there was comparable coverage for PTVs in both techniques for pelvis cases but for head and neck cases PTV receiving 95% dose was 96.14 ± 0.99% and 94.26 ± 1.07% for dynamic and SS techniques respectively. The maximum dose received by PTV for pelvis cases was 106.86 ± 0.25% and 106.65 ± 0.27% for SW and SS techniques respectively and the maximum dose received by PTV for head and neck cases was 107.71 ± 0.38% and 107.99 ± 0.29% for SW and SS techniques respectively. For the two sites studied, there was no significant change in Uniformity Index and Homogeneity Index values for both dynamic and SS techniques. However, there was significant difference observed in Conformity Index for pelvis as well as head and neck cases in both methods. The number of Monitor Units were also less in the step and shoot technique in comparison to the dynamic delivery for both the sites.

Discussion: The study indicates that the difference in PTV coverage was not significant in pelvis cases for both the techniques but it doesn't follow the same trend for head and neck cases. The doses to OARs were lower in the SS technique for pelvis cases but no significant difference was found in head and neck cases.

   P-65: Set-Up Accuracy in Dose Distribution: Comparison Between CT-AND CBCT-Based Plans for Oropharyngeal Cancer Top

Masakazu Otsuka1, Hajime Monzen1,2, Kazuki Ishikawa2,3, Kenji Matsumoto1, Mikoto Tamura1, Tamaki Nishi1 Masahiko Okumura2, Yasumasa Nishimura3

1Department of Medical Physics, Graduate School of Medical Science, Kindai University, 2Department of Radiology, Kindai University Hospital, 3Department of Radiation Oncology, Kindai University Faculty of Medicine, Higashiosaka, Japan. E-mail: [email protected]

Introduction: Oropharyngeal cancer patients are treated with the two-step intensity modulated radiotherapy (IMRT) in our institution. Deformable image registration (DIR) is a critical technic in adaptive radiotherapy (ART) for propagating contours between planning computerized tomography (CT) images and treatment CT/cone-beam CT (CBCT) images to account for organ deformation for treatment re-planning.

Objection: The aim of this study was to investigate an influence factor for the oropharyngeal cancer ART using weekly CBCT.

Materials and Methods: We employed the Exactrac and Varian's On-Board Imager (OBI) for image matching. Ten patients with oropharyngeal cancer were enrolled. The CBCT were used to estimate the dose distributions during the treatment. Planning Target Volume (PTV), spinal canal, brain stem and parotid gland (R, L) were propagated from pre- to mid-treatment images using DIR. The dose between pre-treatment plans and CBCT plans were evaluated by body weight, body surface contour and set-up errors.

Result and Discussion: The differences of mean dose for PTV, spinal canal, brain stem, and parotid gland (R, L) in the maximum weight loss of 8.9 kg were 1.5%, 0.3%, -0.1%, 1.7%, and 8.3% respectively, while in the maximum set-up error of rotating 3.5° at mandible bone, the differences were -1.3%, 1.2%, 5.3%, 2.6%, and 12.5%, respectively. The maximum change in body surface contour was observed the same patient of maximum weight loss. The high set-up accuracy (less than rotating 1° at mandible bone) was found that the differences were less than 2% in PTV, spinal canal and brain stem. Set-up accuracy was higher influence to dose distributions than body weight and body surface contour.

Two-step IMRT is used for dose escalation of parotid gland occurs due to body weight and body contour loss. However, set-up accuracy of patients had the most influence on dose distribution in this study. The most important factor was set-up accuracy of patients in ART, namely strategies for set-up are necessary at CT-simulation and treatment. Set-up accuracy of a patient should be performed ART according to loss of body weight and body contour.

   P-66: Dosimetric Evaluation of Titanium in 16-BIT Depth and 12-Bit Depth: Monte Carlo Study Top

J. Jayapramila, A. A. Mohd Zahri

Oncology & Radiological Sciences Cluster, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Penang, Malaysia. E-mail: [email protected]

Introduction: Accuracy of currently available algorithm for treatment planning system is limited and require full mode algorithm to know the true dose distribution. Monte Carlo (MC) algorithm in radiotherapy is the most accurate approach to perform radiation dosimetry calculation.

Objectives: This study compare dosimetric analysis of titanium rod in 12-bit depth and 16-bit depth DICOM image using MC code of linear accelerator (LINAC) Elekta Synergy.

Materials and Methods: Titanium rod was scanned in two computed tomography (CT) scanners (SIEMENS Somatom (12-bit depth); TOSHIBA Aquilion (16-bit depth)) at 120 kV using in-house built phantom. CT images transferred to MONACO treatment planning system (v.5). Anterior oriented beam plan consisted of 10 x 10 cm3 generated. Collapsed cone (CC) algorithm was applied to deliver 200 MU EGSnrc MC simulation was validated first by comparing percentage depth dose and beam profile on water phantom. BEAMnrc/DOSXYZnrc MC codes with 5 x 108 particle histories traversing titanium rod in 10 x 10 cm3 anteriorly. Point dose evaluation was carried for 12-bit depth and 16-bit depth DICOM images.

Result and Discussion: CT number for titanium rod in 12-bit image saturated at 3071 Hounsfield Unit (HU), whereas for 16-bit depth, mean CT number was 9996 HU. MC simulation is well matched with measured data (PDD and beam profile) with percentage difference of less than 2%. Treatment planning system comparison was compared with MC simulation with presence of titanium rod.

Conclusion: MC code for Elekta Synergy will be a benchmark for this institute. This code give confidence to the physicist to plan and deliver the treatment to patient accurately. 16-bit depth provide accurate dosimetric output than 12-bit depth.

   P-67: Radiation Shielding Application of Lead Glass Top

R. Nathuram

Ex-Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Nuclear medicine and radiotherapy centers equipped with high intensity X-ray or teletherapy sources use lead glasses as viewing windows to protect personal from radiation exposure. Lead is the main component of glass which is responsible for shielding against photons. It is therefore essential to check the shielding efficiency before they are put in use. This can be done by studying photon transmission through the lead glasses. The study of photon transmission in shielding materials has been an important subject in medical physics and is potential useful in the development of radiation shielding materials. In order to make use of the photon attenuation by HP Germanium gamma spectrometer. The counting setup used in the present measurements consists of a narrow beam collimator coupled to a HP Germanium gamma spectrometer. The experiment consists of measuring the ratio of photon beam intensity I, transmitted through an absorber of known thickness t, expressed in units of to the photon beam intensity I0 incident on it. Then the value of attenuation coefficient μ is obtained from the relation:-

I / I0 = e-μt

Each radioactive sources of Cs-137 and Co-60 were selected for the present study as they are used as teletherapy sources in radiotherapy department. Each chosen source of about 200 kBq in solid disc form was in turn placed in front of a lead collimator of 2 mm diameter. The photon beam leaving this collimator passed through the absorber and another identical collimator before being detected by a HP Germanium detector. The photon spectrum of transmitted and incident beam with and without absorbers were recorded on a 8K MCA. From the ratio of transmitted to incident photon beam I/I0 and thickness 't' of the absorber, the value of attenuation coefficients were obtained. In [Table 1], the experimental value of attenuation coefficients obtained against photon energy of each source used in the present investigation are presented compilation of shielding factors of lead viewing glass of known thickness.
Table 1: Photon attenuation coefficients for lead glasses

Click here to view

   P-68: SBRT of Kidney: Our Initial Experience Top

R. Phurailatpam, S. Balara, S. V. Jamema, S. N. Paul, K. Joshi, D. D. Deshpande1

Department of Radiation Oncology, ACTREC, 1Department of Medical Physics, TMH, Tata Memorial Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Aim: To report our Initial Experience on Volumetric-Modulated Arc Therapy (VMAT) of SBRT Kidney.

Materials and Methods: Stereotactic body radiation therapy (SBRT) represents a novel treatment approach in the setting of renal cell carcinoma (RCC). Three patients of RCC already treated with VMAT, True Beam (Varian) were taken for this study. Three VMAT plans for gantry rotation angles of 360° and 180° viz 2 full-arc with flattening filter less 10 MV photon (2FA_10FFF), 2 half-arc with flattening filter less 10 MV photon (2HA_10FFF), 2 full-arc with flattening filter less 6 MV photon (2FA_6FFF) were created for each patient with the Eclipse treatment planning system (version 13.5). Dose prescription was 45Gy/3 fractions. Full-arc and half-arc VMAT plans were compared with regard homogeneity index (HI), coverage index (CI), Conformation Number (CN), dose to OARs (Spine, Duodenum, Stomach), total monitor units (MU), effective dose rates, delivery times, and gamma passing rate for delivery QA for each plan. Delivery QA for each plan is carried out using Arc check dosimetry (Sun NuclearTM).

Result: The HA plans achieved comparable HI, CI and CN to the FA plans. 2HA_10FFF resulted in 30% less MU and 50% shorter delivery time than 2FA_10FFF. Low dose volumes for normal tissues (V5 and V10) are upto 200cc more in 2FA_10FFF than in 2HA_10FFF. Maximum Dose to Spine, Duodenum, Stomach, are also 12%, 35% and 30% lesser in 2HA_10FFF plans than 2FA_10FFF. However for 2FA_10FFF and 2FA_6FFF plans, there is not much difference in dose to OARS and in treatment delivery time between the two plans as shown in [Table 1]. Delivery QA of all the plans were passing with 99% in 2% and 2 mm criteria.
Table 1: Plan parameters

Click here to view

Conclusion: 2HA_10FFF is more efficient than 2FA_10FFF in terms of treatment delivery and OAR sparing. However, there is no difference between 2FA_10FFF than 2FA_6FFF.

   P-69: Comparison Between Single and Double Volumetric Arc Therapy Technique in the Treatment of Cervix and Bot Cancer Top

Amit Saini1, Avtar Singh1, Shefali Pahwa1, Ashok Kumar1, D. D. Deshpande2, Tapas Dora1

1Department of Radiotherapy, Homi Bhabha Cancer Hospital, Sangrur, Punjab, 2Department of Medical Physics, Tata Memorial Hospital, Parel, Mumbai, India. E-mail: [email protected]

Introduction: Volumetric modulated arc therapy (VMAT) is a novel radiation technique, which can achieve highly conformal dose distribution with improved target volume coverage and sparing of normal tissues compared with conventional radiotherapy techniques. VMAT is a new form of IMRT, which allows irradiation with the simultaneously changing gantry position, dose rate and multileaf-collimator (MLC) position. VMAT also has the potential to offer additional advantages, such as reduced treatment delivery time compared with IMRT.

Aims and Objectives: The aim of this study was to investigate volumetric-modulated arc therapy (VMAT) with single arc (1 ARC) and dual arc (2 ARC), and to evaluate the quality. The quality of these plans was evaluated by calculating the quality index (QI) homogeneity index (HI), conformity index (CI), dose to PTV and dose to OAR. For the delivery efficiency of these plans, the numbers of monitor units (MUs) were evaluated.

Materials and Methods: A total of 15 patients (7 with cervix and 8 with base of tongue (BOT) were taken for this study. Patient's plans were created with single and dual arc on Monaco 5.1 Treatment Planning System. For comparison same VMAT planning constraints were utilized in all the single and dual arc plans for each patient and typical dose distribution is shown in [Figure 1]. All the plans had been calculated with constant dose calculation grid size of 3 mm using monte-carlo algorithm. After which dose volume histogram data used to calculate quality index (QI) homogeneity index (HI), conformity index (CI), dose to PTV and dose to OAR.
Figure 1: Dose wash (lowest isodose line is 10%)

Click here to view

Results: As form the tables it was clearly shown that, in cervix as well in BOT cases we evaluated that quality index (QI) homogeneity index (HI), conformity index (CI) were much better in dual arc as compared to single arc. Whereas, MU delivered and Coverage to PTV in dual arc were also more. There were not such big difference in the doses of Organ at Risk (OAR).

Conclusion: In comparison to the VMAT plan with one arc, the VMAT plan with multiple arcs has more control points that give higher degree of freedom for possible MLC positions. This could result in higher degree of modulation and better plan quality, especially for a complex-shaped target volume. However, a higher degree of modulation generally increases the planning time due to longer plan optimization and dose calculation processes.

   P-70: Dosimetric Verification of Total Skin Electron Therapy by Using CASO4 :DY Thermoluminescence Powder in Indigenous Wax Phantom Top

T. Natarajan, A. Chougule1, T. Senthil Kumar S. Venugopal, Umra Fatima, Jeev Raj Bhati, K. Ratheesh, Rajkamal

Department of Radiation Oncology, Bhagwan Mahaveer Cancer Hospital and Research Centre, 1Department of Radiological Physics, SMS Medical College and Hospital, Jaipur, Rajasthan, India. E-mail: [email protected]

Indroduction: The aim of the study is to verify the six dual field Total Skin Electron Therapy radiation technique by using CaSO4:Dy thermoluminescence powder in indigenously prepared wax phantom. This radiation technique is used for the treatment of mycosis fungoides.

Materials and Methods: The study involves the characteristics of the electron beam such as energy, dose rate, flatness at 100 SSD and Extended SSD at 400 cm. The electron beam with gantry angle 270±18.5 for 6MeV with HDTSe- mode which produces dose rate of 888 MU/Min is used for all the measurments. Parallel Plate Chamber is used for dose rate measurement in indigenously prepared wax phantom [Figure 1] which mimic the patient and vertical movement stand [Figure 2] uesd for vertical profile. TLD Reader is used to estimate the dose deposited in CaSO4:Dy powder and 6 mm PMMA acrylic sheet [Figure 2] is used as a energy degrader.
Figure 1: Position of Parallel Plate Chamber in waxphantom

Click here to view
Figure 2: 6 mm PMMA and phantom stand for vertical profile movement

Click here to view

Results: The horizontal and vertical profile was measured and the flatness is found within ±10% as shown in Graphs 1 & 2. The dose rate for six dual field was measured by determining factor A (=0.97061) and factor B (=3.1363) to find the required MU to deliver the prescribed dose.

Discussion: It was found that the required MU to deliver 200cGy at 400 cm SSD for each beam of 6MeV electron with HDTSe- mode is 504 MU. The areas in which the TLDs received less prescription dose is treated as a underdose area and those areas of the patient skin is treated with normal electron mode with 100 cm SSD.

Conclusion: Six dual field dosimetry was performed using CaSO4:Dy thermoluminescence powder in indigenously prepared wax phantom and it is satisfactory method for verification of Total Skin Electron Therapy.

Acknowledgement: The author wish to acknowledge Department of Radiological Physics, SMS Medical College and Hospital, Jaipur for their valuable suppot.

   P-71: Dosimetric Comparison of Epid and Octavius Array for Volumetric Modulated Arc Therapy and QA of VMAT Top

Felix M. S. Vijayan

Department of medical Physics, Anna University, College of Engineering, Chennai, Tamil Nadu, India. E-mail: [email protected]

Aim: The main aim of this study was to assess the reliability of VMAT delivery and compare the dosimetric technique of the portal dosimetry system and Octavius 4D phantom dosimetry for patient specific QA.

Materials and Methods: Dosimetric study has been performed by using the clinac iX, which is operated in the range of 6 MV. For the Patient specific QA, we have selected 7 patients and planned in TPS. These plans recalculated on EPID and Octavius 4D. Thimble chamber 0.65CC was used for measuring high-energy photon and electron radiation in air/in phantom material and also PTW 2D-Array were used. To assess the reliability of VMAT delivery, the accuracy of parameters such as variable dose rate, variable gantry speed, and dynamic MLC during gantry rotation were assessed using EPID.

Result and Discussion: For the comparison of these two dosimetric equipment's used the gamma analysis for the portal dosimetry system, and we found on an average value 98.4% of the pixels passed the criteria of 3%, 3 mm gamma with a standard deviation of 0.82 and with the 4D Octavius system, on an average value 99.37% of the pixels passed the criteria of 3%, 3 mm gamma with a standard deviation of 0.62 for rapid arc and the result shows that, both the systems can be used for patient specific QA measurements for rapid arc. The current study shows that the patient specific QA for VMAT, no significant differences were observed in the rapid arc gamma results of portal dosimetry as well as in the Octavius array system.

Conclusion: We conclude that the QA can also be carried out by EPID and 2D array for the routine patient specific QA in VMAT Radiotherapy.

   P-72: Measurement of Small Irradiation Relative Dose with Various Detectors for 6 MV Photon from Clinical Linac Top

Santunu Purohit, S. M. Enamul Kabir1, Md. Shakilur Rahman2, Md. Kawchar Ahmed Patwary3, A. K. M. Moinul Haque Meaze, Debasish Paul2

Department of Physics, University of Chittagong, Chittagong, 1Department of Radiotherapy, North East Medical College Hospital, Sylhet, 2Secondary Standard Dosimetry Laboratory, Bangladesh Atomic Energy Commission, Dhaka, 3Department of Physics, Comilla University, Comilla, Bangladesh. E-mail: [email protected]

Now a days, modern radiotherapy techniques such as IMRT, IGRT, SRT/SRS etc where proper commissioning of Clinac is challenging due to absence of protocol in dosimetry of small field (where Bragg gray cavity theory actually does not exist). Relative dose of small fields were measured using Cross Calibration Factor (CCF) method and Daisy Chaining Output Factor (DCOF) method using different IBA Chambers. The absolute dose at 10 cm × 10 cm was measured with CC13 (ionization) chamber by IAEA protocol TRS-398. Afterward CC13 chamber was cross calibrated with CC01 (Ionization) and Razor (diode) chamber respectively for the measurement of dose in small fields. According Daisy Chaining factor method, CC13 (ionization) to Razor (diode) dose was also measured. The reference dose of small field was measured using CC13 (ionization) chamber applying newly proposed formalism (R. Alfonso et al . 2008). By introducing cross calibration and Daisy Chaining factor method, it was experimentally found that dose measured with Daisy Chaining factor method technically more suitable and closer result with small field reference dose. During cross calibration factor technique, the dose variation was measured in between CC01 (ionization) and Razor (diode) chambers which found to be close to 4% at field size close to 1 cm × 1 cm, 100 cm SSD and 10 cm depth. The correction factors of Razor chamber for small fields (less than reference size) were measured using CC13 (ionization) chamber. Uncertainties arises in this work both Type-A and Type-B were considered. Finally, combined standard uncertainty was measured 1.51% (1σ). Experimentally it was found that Diode dosimetry is suitable for small field dosimetry for measuring escalated low energy dose in penumbra region. Dosimetry of small field due to source occlusion effect, dose at the centre of field is falling down. In our recent work, it was experimentally found that special attention is needed when field size is close to 1 cm × 1 cm field. Because in 1 cm × 1 cm field, proper positioning of small volume ionization chamber is a challenging task. Most of uncertainties were introducing in dosimetry actually from calibration certificate and beam quality correction factor.

   P-73: Dosimetric Studies of Mixed Energy (6 and 10MV) of FF and FFF Photon Beam on Rapid Arc Radiotherapy Planning Of Carcinoma of Cervix Top

U. G. Ramanjaneyulu, G. Sri Krishna

MNJ Institute of Oncology and Regional Cancer Centre, Hyderabad, Telangana, India. E-mail: ugraman9

The objective of this study was to compare the dosimetric influence of filtered and flattening filter free beam of mixing 6MV and 10MV energy photon beam on the quality of Rapid Arc radiotherapy (RA) plans for patients with Cervical cancer. For this study, plans were created for all patients following Radiation Therapy Oncology Group (RTOG) guidelines. The prescribed dose (PD) of 50Gy in 25 fractions was given. The plan having coverage of 95% of PTV receiving 95% of prescribed dose was accepted. The plans were compared on the basis of planning target volume (PTV) coverage (dose to 2%, 98% of target), Constraints of OAR (Organs at Risk) were volume of 40% <40 Gy for normal bladder and rectum. Apart from this, homogeneity indexes (HI), conformity index (CI), total number of monitor units (MUs) and integral dose to normal tissue (NTID) were calculated to analyze plan quality. The present study reveals that the quality of plan is better for FF beam over the FFF beam in case of Cervical Cancer. Only treatment time decreases in case of FFF beam because of high dose rate.

   P-74: Radiotherapy For Carcinoma of Bilateral Breast Top

Kirti Tyagi, Sachin Taneja, Deboleena Mukherjee, Arti Sarin1

Radiation Oncology Centre, INHS Asvini, 1Nuclear medicine Department, INHS Asvini, Mumbai, Maharashtra, India. E-mail: [email protected]

Objective: Breast cancer is the most common malignancy amongst females in the world, including Indian females. Cancer in both breasts is an uncommon presentation. Incidence of bilateral breast cancer (BBC) has been reported in the range of 1.4–11.8% with the majority being metachronous cancer. In this study we are discussing the effect of post operative radiotherapy in a patient presented at our centre with synchronous bilateral breast cancer.

Materials and Methods: Treatment in patients with BBC is similar to that in patients with unilateral breast cancer wherein adjuvant radiotherapy (RT) forms an integral part of the breast conservation algorithm. Adjuvant RT for breast cancer typically includes whole breast irradiation after lumpectomy or chest wall irradiation after mastectomy with or without regional nodal irradiation. This is accomplished using conventional bi -tangential portals that include part of the anterior chest wall adjacent to the RT target 4-6. RT delivery in cases of SBBC is even more complex owing to multiple field junctions, which results in heterogeneous dose distributions as well as significantly higher irradiation volume of organs at risk (OARs) such as the lungs and heart. A 63 yrs female with carcinoma breast (right and left) was evaluated for receiving external beam therapy. She had been managed with 2 cycles of neoadjuvant chemotherapy followed by bilateral modified radical mastectomy. Histopathology confirmed infiltrating lobular carcinoma ypT2N1 on left side and ypT3N2 on right. After completion of another 2 cycles of planned adjuvant chemotherapy, she was planned for sandwich radiotherapy in view of large volume disease with close posterior margins. The radiotherapy was planned with medial and lateral tangential fields and supraclavicular field with the help of CT markers applied manually. A dose of 50Gy/25# (in 2Gy daily fractions) using 6 MV linear accelerator was prescribed as post mastectomy. During the course of radiation treatment the patient was taken up for clinical evaluation, verification of patient position on treatment couch and port film checks of the treatment field.

Conventional Planning: Conventional plans were made for each side respecting principles of conventional bi-tangential treatment planning consisting of two opposed tangential beams of 6-MV energies for unilateral breast RT with at least 0.7 to 1.0-cm gap between medial tangential portals of both sides. All plans were made on the treatment planning system ONCENTRA™ (M/s Elekta) for treatment on a Siemens Primus Hi Linear accelerator. The heart was spared by using multi leaf collimators (MLCs) whenever possible without compromising target volume coverage. Bolus was not used for any chest wall planning. The plan of each side was summated and the sum plans were evaluated respecting the International Committee on Radiation Units and Measurements (ICRU) criteria and disregarding contours.

Results and Discussion: The radiotherapy planning in this case was highly demanding due to huge target volumes and bilateral involvement of lungs and heart. In the study for our patient an arm support was used and no breast immobilisation system was used. The combined lung volume receiving 20 Gy was 3.28%. A dose of 2.87 Gy was in total delivered to 33% of the heart. Radiotherapy treatment was completed in time. Apart from mild acute skin reactions, no significant acute radiotherapy side effects were observed.

Conclusion: More numbers of patients with long term follow up is required to give a conclusion about radiotherapy treatment in post operative radiotherapy patients of bilateral breast carcinoma.

   P-75: Volumetric Intensity-Modulated Arc Therapy VS. Conventional Intensity-Modulated Radiation Therapy in Lung Cancer: A Dosimetric Study Top

Gangarapu Sri Krishna1,2, Vuppu Srinivas1, Palreddy Yadagiri Reddy2

1MNJ Institute of Oncology and Regional Cancer Centre, 2Department of Physics, Osmania University, Hyderabad, Telangana, India. E-mail: [email protected]

Dosimetric comparisons between Rapid Arc (RA) and conventional Intensity-Modulated Radiation Therapy (IMRT) techniques for left sided lung cancer were performed to address differences in dose coverage of the target, sparing of organs-at-risk (OARs), delivery of monitor units (MUs) and time, to assess whether the RA technique was more beneficial for treatment of lung cancer. 15 lung cases were taken for the study. Originally all plans were created using AAA algorithm (AAA) and the patients were treated using Intensity Modulated Radiotherapy (IMRT). Again all 15 cases were re-planned using RA technique. The evaluated plan parameters were PTV coverage at dose at 95% volume (TV95) of PTV (D95), the dose at 5% of PTV (D5), dose maximum (Dmax), the mean dose (Dmean), the percent volume receiving 5Gy (V5), 20Gy (V20), 30Gy (V30) of normal lung at risk (Left Lung-GTV), the dose at 33% volume (D33), at 67% volume (D67) and the mean dose (Gy) of Heart, the dose maximum (Dmax) of spinal cord. Also, Homogeneity index (HI), Conformity index (CI) and integral dose to normal tissue (NTID) were evaluated to check the quality of the plans. The advantages and disadvantages of RA over IMRT were presented in this paper.

   P-76: Comparative Study of Dose Distribution in 3D Conformal and Simulated 2D Plan of Lung Carcinoma Top

Adhikari Matrika Prasad, M. Thapa1, P.P. Chaurasia, C. S. Shrestha

B.P. Koirala Memorial Cancer Hospital, 1Birendra Multiple College, Bharatpur, Nepal. E-mail: [email protected]

Background: In this modern era, Radiation therapy is adopting newer and newer technology. In our center we have started 3DCRT in 2007. Undoubtably 3DCRT would be better choice of treatment than 2D system. We have tried to find the dose variation in 2D and 3DCRT plans and evaluate the plans with conformity index and heterogeneity index.

Objective: To compare the 3DCRT and simulated 2D plan and evaluate them by studying the dose conformity and dose heterogeneity between these plans.

Materials and Methods: This is a hospital based retrospective study.25 patients with lungs carcinoma were taken for this study. Eclipse treatment planning system is used to create both 3D and 2D plans. Both plans were prepared on the same patient body. The acceptable plans were optimized and compared for dose distribution. The conformity index and homogeneity index were calculated using the following relations from ICRU guidelines.

Results and Conclusion: The Conformity Index (CI) for 3D plan varies from 0.90 to 0.99 which indicates the less variation and hence better coverage of PTV while for 2D plan it varies from 0.56 to 0.99 indicates the poor coverage in many cases. The Heterogeneity Index (HI) value for 3D plans varies from 0.095 to 0.26 indicating less heterogeneity and hence less hot and cold spot, while in 2D plans it varies from 0.080 to 0.46, with indication of poor coverage and more hot and cold spots.

   P-77: Simple Method to Correct for Pitch in a Non 6D Couch for a Frameless Stereotactic Treatments Top

V. K. Sathiya Narayanan, Amit A. Nirhali, Pooja V. Moundekar, Mithun Sajeev, Surendra Pawar

Department of Radiation Oncology, Ruby Hall Clinic, Pune, Maharashtra, India. E-mail: [email protected]

Introduction: Stereotactic treatments has been in vogue for more than 3 decades and efforts were always made to reduce the errors in delivery by introducing a good number of quality assurance methods. The introduction of volumetric imaging before treatment delivery facilitated frameless stereotactic treatments. But, correcting for rotational errors required 6D couch. However, there are publications which show that 6D couch is an expensive technology and it is one among the many factors that contribute to the accuracy and its absence is not a major factor. In our setup, we have been performing stereotactic treatments with couches which has only translational movements. After introducing volumetric imaging and performing frameless stereotactic treatments, we found that rotational errors also need to be addressed. Out of the three rotational errors such as pitch, yaw and roll, we found that pitch is a rotational correction which is a dominant systemic error, has a significant role and it is addressed in our work.

Aim: The aim of this communication is to describe a simple method to address pitch rotation in non 6D couch and hence make the frameless stereotactic treatments of very high accuracy.

Materials and Methods: Siemens Oncor impression Plus machine which has the unflat beam and a Moduleaf tertiary mMLC is used for delivering stereotactic treatments. However, once, the tertiary mMLC leaf which has the leaf width of 2.5 mm is mounted, the size of the volumetric imaging becomes limited to a diameter of 10 cm with a length of 10 cm, which is not sufficient. Hence, we proposed a method of not mounting the Moduleaf, performing Carbon target based MV volumetric imaging, marking the laser centres then rotating the couch using column rotation and then mounting the Moduleaf for treatment delivery. The different sagging properties of CT couch and treatment couch introduces a systematic error of pitch. To quantify the tilt, we use a digital inclinometer which has a resolution of 0.1°. We use Somatom 6, which is a 6 slice CT for acquiring planning CT images. When the patient is with the localiser box on CTcouch, we find the inclination and it is usually between 0.4° to 0.5°, depending on the patient's weight. After the plan, when the patient is positioned for treatment, before the volumetric imaging is acquired, the pitch (tilt) is introduced. The Siemens couch Tx550 is used and the couch mount for stereotactic treatments, has the provision to control the pitch which is done using the tilt knob. We introduce the same tilt (0.4° or 0.5°) by using the digital inclinometer. By this method the pitch rotation is completely eliminated.

Resuts: We have so far implemented the idea of measuring the sag in CT couch with the digital inclinometer and introducing the same sag on the treatment table. The couch mount has this facility for introducing the tilt and the simple digital inclinometer with the resolution of 0.1° helps in introducing the same tilt just before imaging and this helps in eliminating the pitch.

Discussion: By preparing the double layered masks, it is easier to reduce the roll and yaw to the minimum. However, the systemic component of the pitch is due to the different couch sagging levels and pertains to the two couches that are involved in this situation. By using 3 linear and one rotational or angular correction, the delivery accuracy of the treatment can be brought to very high levels. The pitch can also occur due to the improper reproducibility of the patient inside the mask. However, this can be eliminated by taking special care while preparing the double layer mask.

   P-78: Estimation of Cumulative Surface Dose with FFF Beams from Linear Accelerator & Tomotherapy for SBRT of Ca_Prostate: A Phantom Study Top

Lilawati Meena, R. A. Kinhikar, Priyadarshini Sahoo, C. M. Tambe, D. D. Deshpande

Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Flattening filter free (FFF) beams are widely used for the treatment of lung, liver and prostate sites i.e. in Stereotactic Body Radiotherapy (SBRT) techniques. These treatments may be delivered either with linear accelerator or tomotherapy or other modalities like Cyberknife. High dose per fraction (≥7Gy) is delivered to the isocentre of PTV. So, it is important to know the dose received at the surface of patient using Rapidarc technique in Truebeam and rotational IMRT in Tomotherapy.

Objectives: To estimate the cumulative surface dose variation between 6X FFF energies of two different modalities i.e. Varian Truebeam and Accuray Hi-Art Tomotherapy. Also, variation between two energies i.e. 6X FFF and 10X FFF of Varian Truebeam using Rapidarc technique.

Materials and Methods: TLD-100 (LiF:Mg, Ti) was used for the measurements with Varian Truebeam linear accelerator and Accuray Hi-Art Tomotherapy. Five patients who have been already treated with Ca_prostate were selected for this study. Body phantom of dimension 30X90X20 cm3 was assembled using different slabs of different dimensions. Phantom verification plans were created from the final approved plans. Then, those plans were made to run on the phantom created by various slabs. The total dose of 7Gy was delivered at the isocentre. In 10X FFF plans, two arcs were used one running in clockwise and the other one running in anti-clockwise direction from 1790-1810 and collimator angles used were 300, 3300 . The tomo plans were made using field width of 2.5 cm, modulation factor of 2.5 or 2 and pitch of 0.3. TLD's were read with Rexon reader after 24 hours of exposure and readings at different distances were recorded. Calibration of TLD was also done using Elite-80 cobalt machine. TLD's were placed at isocentre and laterally on both sides at 7.5 cm distance from isocentre, and at depth of 5 cm and 10 cm on left and right side.

Results: Mean surface dose delivered with 6X FFF energy from Truebeam was 11.33% ± 3.43 of the prescribed dose of 7 Gy in single fraction whereas the surface dose delivered by Tomotherapy was 10.89% ± 1.3 of the prescribed dose. Mean surface dose delivered with 10X FFF energy of Truebeam was 9.48% ± 2.88.

Conclusion: Among two advance technologies delivering rotational IMRT with 6X FFF, there was no significant difference. Surface dose delivered by 6X FFF energy linear accelerator was slightly higher compared to Tomotherapy. Among two different beam energies of 6X FFF and 10X FFF, 10X FFF energy certainly showed reduction in surface dose by 2% compared to 6X FFF. But the deviation observed in the surface dose delivered by tomotherapy was less compared to Truebeam.

   P-79: Stereotactic Body Radiotherapy (SBRT) for Metastatic Spine Tumours Using High Intensity Flattening Filter Free (FFF) Photon Beams - A Planning Comparison With Flattened Photon Beam Top

T. Moorthi1,2, K. Balaji1, S. Balajisubramanian1, P. Sumana1, K. Sathiya1, D. Khanna2

1Department of Radiation Oncology, Gleneagles Global Hospitals, Chennai, 2Department of Physics, Karunya University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: Vertebral metastases are a common and progressive disease can result in pain, neurological disability and reduced quality of life. A recent development is the application of high precision stereotactic body radiotherapy (SBRT) for spinal metastases. Several reports indicate that durable improvement in pain control are possible with long-term local control by giving radiotherapy.

Objectives: To compare SBRT treatment for metastatic spine tumour using high intensity unflattened and flattened photon beams.

Materials and Methods: VMAT based SBRT treatment plans were generated for 10 metastatic lumbar spine patients using 6X-FFF, 10X-FFF and 6X-FF photons of TrueBeamSTx linear accelerator (Varian medical systems, USA), modeled in Eclipse Treatment Planning System (Version13.7). 8Gy in single fraction was delivered to the target volume using 1 full arc for 6X-FFF and 10X-FFF and 3 full arc for 6X-FF. Dose calculation was performed with Anisotropic Analytical Algorithm (AAA). All plans were normalized to 100% in target mean.

Comparison of plans generated has been established in terms of various dosimetric variables such as Quality Coverage for PTV (D95% in %), Conformality number (CN), Homogeneity Index (HI), Gradient Index (GI). Organs at Risk (OAR's) like kidneys, liver and small bowel mean doses were evaluated. Technical parameters of delivery such as total number of monitor units (MU) and Beam On time (BOT) were compared. ANOVA test was performed for statistical significance analysis.

Results and Discussion: The Mean ±SD value of Quality of Coverage D95% for 6X-FF, 6X-FFF and 10X-FFF were 94.60 ± 1.30, 93.52 ± 0.68 and 94.16 ± 0.99 % respectively (p=0.07). CN values for 6X-FF, 6X- FFF and 10X-FFF were 0.79 ± 0.04, 0.76 ± 0.03 and 0.80 ± 0.02 respectively (p=0.005). HI values for 6X-FF, 6X-FFF and 10X-FFF were 0.11 ± 0.02, 0.14 ± 0.02 and 0.12 ± 0.03 respectively (p=0.02). GI value for 6X-FF, 6X-FFF and 10X-FFF were 5.33 ± 0.64, 5.43 ± 0.45 and 4.97 ± 0.56 respectively (p=0.163). The Mean ± SD value of spinal cord (D2) for 6X-FF, 6X-FFF and 10X-FFF were 7.7 ± 0.16, 7.75 ± 0.04 and 7.71 ± 0.16 Gy respectively (p=0.783). The mean dose of small bowel for 6X-FF, 6X-FFF and 10X-FFF were 1.83 ± 0.67, 1.69 ± 0.59, 1.67 ± 0.56 Gy respectively (p=0.823). The mean dose of kidneys for 6X-FF, 6X-FFF and 10X-FFF were 1.51 ± 0.65, 1.49 ± 0.65, 1.26 ± 0.53 Gy respectively (p=0.600). The mean dose of liver for 6X-FF, 6X-FFF and 10X-FFF were 0.49 ± 0.52, 0.47 ± 0.50, 0.45 ± 0.50 Gy respectively (p=0.984). All normal organs shows comparable dose values in all plans. This study showed reduced MUs and BOT with improved treatment delivery for SBRT plan using 10X-FFF compared to 6X-FFF and 6X-FF. MU values (Mean ± SD) for 6X-FF, 6X-FFF and 10X-FFF were 1841.60 ± 178.77, 1881.90 ± 131.54 and 1768.00 ± 70.28 MU respectively (p=0.772). BOT values (Mean ± SD) for 6X-FF, 6X-FFF and 10X-FFF were 3.75 ± 0.0, 1.32 ± 0.05 and 1.25 ± 0.0 min respectively (p=0.00001).

The investigation of dosimetric performance and treatment delivery efficiency suggests that 10X-FFF Planning is promised for SBRT in the treatment of metastatic spinal column. Total beam on time is substantially reduced, because of reduced MUs and single arc with increased dose rate delivery with respect to 6X-FF and 6X-FFF. This gain in BOT with 10X-FFF mode adds patient's convenience.

   P-80: National University Hospital of Singapore Experience: Intensity Modulated Radiotherapy Commissioning Based on Task Group 119, a Report from AAPM Top

Y. F. Leong, S. P. Bargarley

Radiation Therapy Centre, National University Cancer Institute, Singapore. E-mail: [email protected]

Introduction: 3D conformal was the standard of care for radiotherapy before intensity modulated radiotherapy (IMRT) started in the late 1990s. Since then, usage of IMRT has been growing rapidly. IMRT involves an inverse planning approach with complex MLC movement and multiple gantry angles. In 2008, the Radiological Physics Center (RPC) irradiated 250 head and neck phantoms and found that 28% failed to meet either 7% dose accuracy in low gradient region or 4 mm DTA in high gradient, or both. This experience suggested that many clinics did not commission their IMRT system adequately. In 2009, Task Group 119 (TG-119) of AAPM produced a set of quantitative confidence limits as baseline expectation values for IMRT commissioning. These confidence limits (CL) were based on collective data from 9 facilities that had passed the RPC credentialing tests for IMRT. Any facility that wants to use these benchmarks should perform the planning, measurement and analysis as suggested by TG-119.

Objective: NUH evaluated its overall IMRT system performance based on the TG-119 guidelines and compared the results to the TG-119 benchmarks.

Materials and Methods: Scans were conducted on 20 cm solid water phantoms with 0.125 cm3 SemiflexTM ionization chamber inserted in the middle. 6 planning cases (multi-target, mock prostate, mock head, mock neck, C-shape easy and C-shape hard) were created using the recommended plan goals and beam arrangements to ensure that the beam modulation produced is similar to the benchmark plans. 2 preliminary tests (AP:PA 10 x 10 open fields and AP:PA five bands 3 cm wide) were planned, delivered and measured to demonstrate the reliability of the assessment system of non-IMRT dose delivery. Chamber measurements were done using 0.125 cm3 SemiflexTM ionization chamber and the agreement between planned and measured doses was determined at high and low dose region. Per-field measurements were measured with ArcCHECK (AC) cylindrical diode array phantom and measured fields were analysed using SNC Patient™ software.

Results: The benchmark confidence limits for chamber measurement at high and low dose region averaged over 9 institutions were 0.045 and 0.047 respectively. NUH achieved confidence limit of 0.040 for high dose and 0.024 for low dose. Benchmark confidence limit for per-field measurements was 7.0 and NUH achieved a confidence limit of 6.8.

Discussion: TG-119 commented that the confidence limits obtained by any facilities performing similar tests should be equal to or less than the confidence limits reported by TG-119. NUH met the benchmarks recommended by TG-119. Performing the TG-119 IMRT commissioning test and being able to meet the benchmarks gives NUH confidence in our IMRT delivery system. Institutions that are going to start new services in IMRT treatment or institutions that wish to evaluate their current IMRT system performance are recommended to perform this specific set of tests.

   P-81: Designing a Novel Phantom for Daily QA of Cyberknife M6 Robotic Radiosurgery System Top

R. Holla, B. Pillai, D. Khanna1

Department of Medical Physics and Radiation Safety, Amrita Institute of Medical Science and Research Center, Kochi, Kerala, 1Department of Physics, Karunya University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Purpose: Performing daily QA on Cyberknife system includes routine linac output constancy and constancy check for energy. Placing the ionization chamber at 80 cm SAD as specified by the equipment supplier for Cyberknife system is difficult since the system is non isocentric. However, birdcage assembly, an assembly and detector mount for holding the ionization chamber at a fixed distance of 80 CM from the the radiation source can be used to monitor the output. But the measurement chamber is placed in air which is not suitable for 6MV photon beams. Hence a new phantom has been designed which can be fixed to birdcage assembly to monitor output and energy constancy in the medium (Polystyrene)

Methods: A polystyrene block of 5 cm thickness is designed to fit in the distal end of the birdcage and this block is drilled to accommodate 0.13cc (PTW, Germany) ion chamber at the dmax depth of 1.5 cm. The source to the chamber distance (SCD) is exactly 80 cm when the phantom is placed in the birdcage assembly. Two more polystyrene phantom blocks of 3.5 cm and 5 cm thickness are cut to fit inside the birdcage assembly. These 3 blocks gives us the measurements at depths of 1.5 cm, 5 cm and 10 cm. Primary calibration has been done in water. Standard readings in the polystyrene phantom are obtained by comparison with water measurements. Measurement at 1.5 cm depth corrected for temperature and pressure represents the output constancy of the Linac. The ratios of the readings 5 cm and 10 cm depths to 1.5 cm depth represent the constancy of beam quality.

Results: Daily measurements are performed with this phantom developed in-house.

Conclusion: Since the phantom is designed to fit inside the birdcage assembly, reproducibility of the setup is found to be very good therefore the readings will truly reflect the performance of the machine.

   P-82: Comparison of Inhomogeneity Effect for Small Field Dosimetry Between 6 MV FF and FFF Photon Beams Using The Egsnrc Monte Carlo Code Top

S. Sangeetha, C. S. Sureka1

Departments of Physics and 1Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: In recent years, a great deal of attempt has been carried out by the researchers on inhomogeneity effect in human body in the field of radiation therapy. Among these studies, accurate dose calculations of inhomogeneous organs such as lung; particularly for small field size has been considered to be the more challenging task in the field of radiation therapy.

Objectives: The objective of the present study is to analyze the inhomogeneity effect of lung region inside the inhomogeneous phantom for small field sizes of FF (Flattening Filter) and FFF (Flattening-Filter-Free) 6 MV photon beams using EGSnrc Monte Carlo user codes.

Materials and Methods: A 6 MV FF and FFF photon beams of a Varian Clinac 600C/D medical linear accelerator for small field dosimetry (0.5 x 0.5 cm2 to 4 x 4 cm2) were performed for homogeneous and inhomogeneous water phantom containing lung using EGSnrc Monte Carlo user codes (BEAMnrc and DOSXYZnrc) in order to calculate the dosimetric beam characteristics. The dimension of the water phantom was 30 × 30 × 30 cm3 with the voxels dimension of 0.5 x 0.5 x 0.5 cm3 and the phase space source position was incident on the water surface at Z=0, so that the distance from the electron beam to the surface of the water phantom (SSD) is 100 cm. In all simulations, the charged particle and photon cut off energies were set as default to be 0.7 MeV and 0.01 MeV respectively and the water used with the density of 1g/cm3 and 0.25 g/cm3 is considered to resemble the material of soft-tissue and lung material in this present work.

Results and Discussion: The results were analysed in determining the inhomogeneity effect of lung region inside the inhomogeneous phantom for small field sizes of FF and FFF 6 MV photon beams using dosimetric beam parameters. The results obtained showed that the edges between inhomogeneity for all field sizes were evidently visible that the absorbed dose gets dramatically reduced in the lung region for FF beams while it gets minimally reduced for FFF beams with small discrepancies. It has been observed that the dose fall-off occurs in the edge between solid water and lung region and further, the dose gets increased in the edge of lung region and solid water for all field sizes. the dose reduction for FF beams inside the lung was found to be 50%, 44%, 23%, 15% and 10% for FF beams whereas for FFF beams, the dose reduction was 13%, 9%, 7%, 5% and 3% respectively for the smaller field sizes of 0.5 x 0.5 cm2, 1 x 1 cm2, 2 x 2 cm2, 3 x 3 cm2, and 4 x 4 cm2. These dose fluctuations occur due to the variation in the density of the materials and due to the yield of secondary electrons. This study depicts that the FFF beams depicted minimal dose reduction in the lung dose region irrespective to the lung dose region in the FF beams for small field dosimetry and thus FFF beams are well suitable in delivering accurate dose calculations for inhomogeneity effect in small field sizes.

   P-83: Does high density artifacts impact Stereotactic Radiosurgery of post endovascular embolization AVM? A Dosimetric analysis Top

A. Jerrin1,2, V. Ramasubramanian2, A. Karuppusamy3, A. Pichandi1, A. Dinesh1, P. S. Sridhar1, N. Madhusudan1, K. Roopesh1

1Cyberknife Center, HCG Enterprises Ltd., Bengaluru, Karnataka, 2School of Advanced Sciences, VIT University, Vellore, Tamil Nadu, 3Department of Radiation Oncology, Apex HCG Oncology Hospitals LLP, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Cereberal Arteriovenous Malformation (AVM) is a tangle of abnormal and poorly formed blood vessel. This condition causes bleeding to surrounding brain and injure the surrounding brain which leads to headache, seizure, stroke or even death. Treatment of AVM relies on multimodality approach predominantly by surgery, stereotactic radiosurgery (SRS) and/or endovascular embolization depending on various condition like location, size, grade etc. Embolization can be used as curative procedure for smaller AVMs, however it is also used as adjuvant for surgery or Radiosurgery. Endovascular approach uses embolization agents such as n-butyl cyanoacrylate (n-BCA) called glue, Ethylene-vinyl alcohol copolymer (Onyx) etc. However post embolized AVMs possess challenges if treated further with radiosurgery due to high density of embolizing agents cause artifacts in CT images which affects the delineation of tumor. Also for small radiosurgical beam these artifacts affects plan quality due to missing tissue information. This study aims at analyzing the dosimetric inaccuracy caused by embolization agent for post embolization AVM radiosurgery treatment.

Objective: To analyze dosimetric impact of missing tissue information from CTdue to the presence of high density embolizing agents in the treatment of post embolization recurrent AVMs.

Materials and Methods: Two patients were presented with recurrent AVM post embolization. The planning CT images were taken with Siemens Biograph CT equipment. At 140 kVp, Hounsfield Unit (HU) of embolization agent oynx is found to be approx. 3059HU. Target and organ at risk delineation were carried out with assistance of MRI secondary images to overcome missing tissue information from CT images. Treatment planning was done with goal of achieving 16Gy to at least 95% Planning Target Volume in single session. In order to access the dose uncertainties caused by missing tissue information from CT, the plans made in original raw CT (RCT) were superimposed on HU enforced CT (HUeCT) imageswith enforced 40 HU to regions of of HU less than -60. Retrospectively, similar SRS plans with Dynamic Conformal Arc therapy (DCAT) and Volumatric Arc Therapy (VMAT) were made with Monaco® planning station for ElektaVersaHD with Apex Micro MLC unit. Treatment plans generated in CTs with and without HU corrections were compared and analyzed. Plan class verification measurements were also done for plans in CTs with and without HU corrections.

Results and Discussion: Dose distribution in two sets of CT images (RCT and HUeCT) were compared. Plan quality were quantified with respect to target coverage, maximum, minimum point dose and gradient scores. Out of three techniques used in this study, CK and VMAT plans on both CT sets varies by approx. 0.5% and DCAT plans varies by 2%. Radiosurgical plan quality evaluated with Gradient Index showed there werelittle changes in dose distribution isotropicallyfor all plan techniques, with VMAT plans having larger gradient up to 4 mm. Maximum dose to Organ at risks (OAR) closer to targetswere underestimatedin RCT and inversely for peripheral OARs.

Conclusion: Overall, all plans in both CT sets satisfy planning goals and there was no clinical significance found. Planning with high density artifact CT does not affect plan quality however care should be taken for OARs in close proximity with target. We suggest planners to set objectives with tight constraints much lower than allowed tolerances for OARs close to PTV.

   P-84: Accuracy of Positioning Errors for Patient Set-Up on SRS or SBRT Top

Jinsook Ha1,2, Taewon Kim1, Mijin Jeon1, Kwangwoo Park2, Bo Young Choe3, Tae Suk suh3, Hong-Suk Jang3

1Department of Radiation Oncology, Gangnam Severance Hospital, 2Department of Radiation oncology, College of Medicine, Yonsei University, 3Department of Biomedical Engineering and Research Institute of Biomedical Engineering, The Catholic University of Korea, Seoul, Korea. E-mail: [email protected]

Purpose: For stereotactic body radiation therapy (SBRT) or stereotactic radiosurgery (SRS), positional accuracy is crucial. We focused on isocentric positional error based on the several angles of gantry and treatment couch. The main purpose is to improve the accuracy of delivered dose for SBRT/SRS by applying offset corrections which are determined by Winston-Lutz test for each angles of gantry and couch.

Materials and Methods: Isocentric offset values are determined by rotating gantry angles (every 15 degree) for each couch angle (335, 15 degree). From the winston-Lutz test, offset values are obtained. As a preliminary study, we performed patient specific quality assurance (PQA) with and without isocentric corrections. For PQA, we measured point dose in high dose region and film image to analize gamma index. The phantom, StereoPhan (sun-nuclear) with A1SL ionization chamber (Exradin) is used. Gamma index analysis was performed using DoseLab Pro (sun-nuclear) with 3 mm/3% criteria.

Results: Based on the preliminary measurement, the accuracy of point dose was improved from -3.34% to -1.8%. Practical target volume is approximately 0.6cc which need a small field size where ionization chamber, A1SL usually measures underdose by volume averaging effect. Therefore, -1.8% is very accurate result. Gamma analysis showed also improvement after applying isocentric corrections. Gamma pass rates are 91% and 94% without and with corrections applied respectively.

Conclusion: We suggested the method which can be applied to actual treatment without work overloading. Isocentric corrections are determined before treatment using Winston-Lutz test, and applied to actual treatment. The result showed the improving accuracy of delivered dose.

   P-85: Detector Accuracy Comparison for Point Dose Measurements in Small Fields Top

Silpa Ajay Kumar, Vipin M, Resmi K, Soumya N M

Department of Radiation Oncology, Malabar Cancer Centre, Thalassery, Kerala, India. E-mail: [email protected]

Introduction: The present aim in radiation therapy is to ensure that the uncertainty in the dose received by a patient does not exceed 5%. Considering all sources of uncertainty, this means that the dose at the calibration point of a Linear Accelerator has to be known to be within 2%. Commonly, a field size of less than 4×4 cm2 is considered other than the conventional treatment field size that needs special attention both in dose measurements and in dose calculations. Small field dosimetry plays an important role in modem radiotherapy for many reasons. For fields this small, the physics of how the radiation is delivered is different from that of large fields and some traditional forms of dosimetry begin to fail. As such, it is imperative that accurate treatment planning and QA can be performed to ensure that these very small fields are being used safely and effectively.

Aim: To find out the suitable detector for point dose measurements in small fields.

Objective: The definition of a small field in radiation dosimetry is currently very subjective. A “small field” is generally defined as a field with dimensions smaller than the lateral range of the electrons that contribute to dose. Small fields are increasingly used in modern radiotherapy especially in volumetric modulated arc therapy and stereotactic radiosurgery treatments. In this study suitability of detector for small field dosimetry is checked.

Materials and Methods: Small field size plans were created in the water phantom in Eclipse treatment planning system version 10.0 at a specified depth (10 cm), These plans were delivered in a water phantom and point doses were measured with different detectors. Measured point doses were compared with point doses obtained from the treatment planning system. Then the detector efficiency is validated using IMRT plans.

All measurements were performed in a Varian Clinac iX linear accelerator equipped with a millennium 120 leaf collimator (Varian oncology systems, Palo Alto, CA) and the results will be cross compared with Eclipse treatment planning system version 10.0.

Results and Discussion: comparison of point dose calculated from the Eclipse Treatment planning system version 10.0 and measured point dose from the four commercial detectors available in our center using Radiation Field Analyzer (RFA) semi flex ionization chamber shows a variation of 6% while for pinpoint ionization chamber and diode detector an average percentage of variation of 2% and 1.5% respectively. A minimum variation of 1% observed with measurement using diamond detector.

Conclusion: Verification of the small field intensity modulated radiation therapy plans for exploring the efficiency of the different types of detectors available in our center concludes, microdiamond detector and diode detector are the excellent choice for small field dosimetry. Microdiamond detector and diode detector shows average percentage of variation less than 1% and 1.5% respectively.

   P-86: Positional Errors in Linear Accelerator Based Frameless Cranial Stereotaxy: A Note of Caution Top

A. Manikandan1,2, C. S. Sureka1, S. Biplab3

1Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, 2Department of Radiation Oncology, Nagarjuna Hospital, Vijayawada, Andhra Pradesh, 3Department of Radiation Oncology, Fortis Hospital, New Delhi, India. E-mail:[email protected]

Introduction: Frameless stereotaxy (SRS/SRT) for cranial tumors has achieved considerable popularity because of its convenience over the invasive frame. BrainLab (BrainLab AG, Feldkirchen, Germany) is a major stereotactic solution provider worldwide which is compatible with both Varian (Varian medical system, Palo Alto, CA) and Elekta (Elekta AB, Stockholm, Sweden) linear accelerators. Frameless stereotactic therapy delivery uses a head and neck extension as a base plate. This base plate is an extension to main couch and attached at the cranial end using two clips as shown in [Figure 1]. With this arrangement, much of the patient's body lies on the main table while the head (with head rest) lies on the extended attachment. Main table and head neck extension are loosely attached to each other and act as a lever of class 1, hence exhibit a depression in the cranial end. This effect is observable in both Varian and Elekta make couches. When the patient lies on the couch, the cranial end of the couch tends to go down due to gravity. This introduces an unacceptably high rotational error about the X (lateral) axis (pitch) and translational error along Z (vertical) axis depending on the position of the tumor.
Figure 1: The laser shift due to cranial sagging attributed to the fulcrum effect in brainlab steriotactic baseplate. The laser shift noted in this particular case was 8 mm for frameless steriotactic cases

Click here to view

Objective: Objective of this work is to find out the need of 6D couch in stereotactic treatment delivery unlike the conventional couches, having only translational movements.

Materials and Methods: In this study we have included the regular brain tumor patients who were treated with all-in-one (AIO) base plate firmly adhered to the main table as shown in [Figure 2]. We assessed the cranial end sagging for regular cases and stereotactic cases for 90 patients by calculating the positional shifts in the three translational directions and the rotational shifts about the three axes.
Figure 2: No cranial sagging when normal base plate was used

Click here to view

Results and Discussion: We found that the mean± standard deviations (SD) for the vertical shifts (Delta Z) were - 0.11 ± 0.18 cm and 0.0 ± 0.48 cm for regular and SRS cases respectively and the mean± SD for the rotational shifts around x-axis (pitch) were 0.33 ± 0.77° and 0.41 ± 1.63° for the regular and SRS cases respectively. However, the SDs for the other translational and rotational axes were comparable between regular and SRS cases. For example, roll mean± SD for lateral (Delta X) shift for regular and SRS cases were -0.01 ± 0.19 cm and 0.08 ± 0.1 cm, respectively; mean± SD for craniocaudal (DeltaY) shift for regular and SRS cases were 0.16 ± 0.21 cm and 0.05 ± 0.17 cm, respectively; mean ± SD of rotational shifts about Y-axis (roll) for regular and SRS cases were - 0.32 ± 1.32° and 0.39 ± 1.05°, whereas that about Z axis (yaw) for regular and SRS cases were - 0.16 ± 1.34° and -0.17 ± 1.17°, respectively. Therefore, we conclude that SRS/SRT patients exhibit a higher positional error in terms of SD in vertical direction and in rotational pitch than that of regular cranial cases due to the use of cranial extension. Higher SD yields a higher setup margin. In the absence of a robotic couch that can account for rotational shifts in addition to the translational shifts, the residual rotational errors can result in unacceptably high error in spatial dose delivery.

   P-87: Measurement of Dose in 6MV and 10MV FF and FFF Photon Beams for Smaller Field Size Top

M. A. Elan, L. Bharanidharan, Prakasarao Aruna, J. Velmurugan, P. Thamilkumar1, R. R. Rai1, Singaravelu Ganesan

1Department of Medical Physics, Anna University, 2Department of Radiotherapy, Dr. Rai Memorial Cancer Institute, Chennai, Tamil Nadu, India. E-mail: [email protected]

Introduction: Small field dosimetry is a difficult task and no consistent data is available for modern radiotherapy techniques. Lateral electronic disequilibrium is an important factor and due to steep dose gradient, there is a high complication of radiation dosimetry for smaller field size. Modern technology in radiotherapy poses high level of uncertainties in small field dosimetry. The size of the detectors plays a vital role for the measurement of small field dosimetry.

Objective: The current study estimates the dose using various detectors like ionization chamber, diode and MOSFET detector as a function of field size.

The parameters like percentage depth dose, beam flatness, symmetry and penumbral width are evaluated for three detectors. Various small field sizes like 1 cm × 1 cm, 2 cm × 2 cm, 3 cm × 3 cm, 4 cm × 4 cm, 5 cm × 5 cm are evaluated for various detectors. The goal of our study is to evaluate the response of three active detectors exposed to 6MV X-ray beams.

Materials and Methods: The Linear Accelerator True Beam with long stand which was calibrated to deliver a dose of 1cGy per MU at 10 cm depth of water, a reference field size of 10 cm × 10 cm and a source to surface distance 100 cm for 6 MV and 10 MV respectively and the detectors used for the measurement were ionization chamber, diode and MOSFET. The phantom used for the study is 30 cm × 30 cm PMMA phantom.

Results and Discussion: Doses were measured using Ionization chamber, Diode detector and MOSFET detector for 6 and 10 MV photon beam with both FF and FFF as a function of field size viz, 1 cm×1 cm, 2 cm × 2 cm, 3 cm × 3 cm, 4 cm × 4 cm, 5 cm × 5 cm are evaluated and measured reading shows that the dose absorbed for 6 and 10 MV photon beam with FF is higher than FFF which may due to higher scatter dose caused due to the flattening filter. The response of the ionization chamber and diode detector is linear. MOSFET over estimates the dose and there was no significant difference.

Conclusion: Our study shows that the dose absorbed in ionization chamber and diode detector were consistent than MOSFET and also from our study it is concluded for FF beams the dose measured were higher than FFF due to high scatter.

   P-88: A Comparison of Two Different Treatment Planning Systems in the Planning of Stereotactic Radiosurgery of Schwannomas Using Unflat Beams Top

S. Karthikeyan, Harikrishna Etti1, S. Maruthu Pandian

Department of Radiation Oncology, BGS Global Hospitals, Bengaluru, Karnataka, 1Department of Medical Physics, Bharathiyar University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Objective: Currently the use of flattening filter-free (FFF) beams or unflat beams operating at higher dose rates which are available on an increasing number of commercial linear accelerators can lead to increased efficiency of treatment delivery especially for the treatment of stereotactic radiosurgery (SRS). There is a need for an assessment of the available treatment planning systems (TPS) in a single institution. This study compares the dose distributions of complex Intensity Modulated Radio Surgery (IMRS) plans produced by two TPSs: Varian Eclipse and Brainlab Iplan.

Materials and Methods: The Study was performed on Varian Eclipse (version 13.7) and Brain lab Iplan (version 4.5.3) which allows planning for 6 MV FFF beams for delivery on Truebeam STx linear accelerator. The two systems were commissioned with the same beam data and, as best as possible, matched configuration settings. IMRS treatment plans for twenty four schwannomas patients were produced on each system with pencil beam convolution (PBC) algorithm in Brain lab Iplan and Anisotropic Analytical Algorithm (AAA) in Varian Eclipse TPSs. All 48 plans were subjected to identical dose constraints, both for the target coverage and organ at risk (OAR) sparing, with a consistent order of priority. All plans were generated with non-coplanar beam geometry in both TPS.

Results and Discussion: Few statistically significant differences were found between the target coverage and OAR sparing of each system, with all optimizers managing to produce plans within clinical tolerances (D2 < 107% of prescribed dose, D5 < 105%, D95 > 95%, D99 > 90%, and OAR maximum doses) despite strict constraints and overlapping structures.

Conclusion: The study compared the plans produced by two TPSs — Eclipse and Brainlab Iplan — for the treatment of schwannomas with non-coplanar beam arrangement using unflat beams. Few statistically significant differences were found, but AAA Eclipse TPS generally gave lower OAR doses, with an integral dose outside the target 26% lower than PBC Brainlab Iplan TPS on average across all patients.

   P-89: Commissioning of Raystation Treatment Planning System Top

B. Surendra

Department of Radiation Oncology, B P Koirala Memorial Cancer Hospital Yagyapuri, Bharatpur-7, Chitwan, Nepal. E-mail: [email protected]

Introduction: The aim of this work is commissioning a collapsed cone (CC) convolution dose calculation algorithm for photons beam for clinical practice by modeling in RaySta-tion (RaySearch Laboratories) treatment planning system.

Materials and Methods: PDDs, profiles, output factors and beam calibration, for beam modeling were measured in a water tank. Pinpoint and semiflex ionization chambers were used for beam scanning and output factor measurement for field size 64 cm x 4 cm and >5 cm x 5 cm, respectively. Farmer IC was used for reference dosimetry. The collected beam data were modeled in RayPhysics TPS module. The agreement of measured and computed beam were evaluated by using RMS difference and flat gamma analysis. Dose calculation algorithm validation has been performed in two steps: firstly, point dose measurements have been compared with calculated ones under reference and non-reference condition. Secondly, a fluence map comparison has been performed. Simple RT plans in water, and phantom as well as seven clinical VMAT plans for prostate, oesophagus, lungs, glioma and oropharynx were computed and measured by means of a PTW Octavius 729 ionization chambers matrix. VeriSoft software was used for gamma analysis. As additional valida-tion, CC dose calculation algorithm has been compared with Eclipse AAA. The DVH and gamma of dosemaps for both algorithms were also evaluated.

Results: Computed PDDs and profiles were found in good agreement with measured ones. The max RMS difference was (10.0 0.4) % in build up region and (7.0 2.5) % in penum-bra region. For FS 6 4 cmx4 cm but both were in tolerance. The gamma analysis of all PDDs and profiles was acceptable. In point dose verification, the measured and calculated point dose differences were found within 1%. In clinical RT plans, the gamma pass rate was above 92%. The gamma, 3%G/3 mm, of VMAT of prostate, and glioma were found 100% and decreased with more complex VMATs like oesophagus (95.7%) and orophar-ynx (92.4%). PTVs and OARs DHVs comparison results of two algorithms were found satisfactory. Maximum dose difference is less than 3%.

Conclusions: The results of validation test for beam model and collapsed cone convolu-tion dose calculation algorithm allowed to conclude that the commissioned CCC can be use for clinical practice.

   P-90: Analysis of Beam Profiles, Percent Depth Dose and Volume Effect in Small Fields Using Different Type of in House Available Ionization Chambers Top

Ramandeep Singh, Pardeep Sharma, Shakhar Dwivedi, M. K. Mahajan

Department of Radiotherapy, Advance Cancer Institute, BFUHS, Faridkot, Punjab, India. E-mail: [email protected]

Introduction: With the advancement in technology in modern radiotherapy, small field dosimetry of photon beam has become the topic of interest. Specialized radiation treatments such as beamlet-based intensity-modulated radiation therapy (IMRT), image-guided radiation Therapy (IGRT), tomo-therapy, stereotactic radiosurgery (SRS) with high-resolution multileaf collimator, Gamma-Knife, and CyberKnife rely on small field sizes of order of a few millimeters to treat tumors and simultaneously spare normal structures. Compared to the conventional radiotherapy with fields ≥4 x 4 cm2, small fields exhibit significant uncertainty in determination of dosimetric parameters. Small field dosimetry of photon beam is challenging task due to lack of lateral electronic equilibrium, source occlusion, high dose gradients, and detector volume averaging. It is recommended that detectors that are tissue equivalent and have small volume are best suited for small field dosimetry. This study includes analysis of dosimetric parameters such as beam profiles and percentage depth dose (PDD) using in-house available ion chambers of different volumes.

Aim and Objective: The aim of the study is to analyze Percentage Depth Dose and Beam Profiles for small field ≤5 x 5 cm2 by using the different type of ionization chamber and their volume averaging effect in small field dosimetry of photon beam of energies 6 MV, 10 MV and 15 MV.

Materials and Methods: The study is being performed on Varian True beam medical linear accelerator using radiation field analyzer (RFA), a water phantom with dimensions 673 mm height, 875 mm width, 676 mm diameter of ring with integrated software (SNC dosimetery) version 3.2 from Sun Nuclear corporation and ionization chambers i.e. PTW Farmer chamber, SNC125c chamber, Markus chamber and PTW Pinpoint chamber. Different field sizes are opened from 1 x 1 cm2 to 5 X 5 cm2 with jaws and multileaf collimator along with standard field size 10 x 10 cm2. For each field size beam data acquired using RFA. PDD and Beam profile data has been acquired with all the chambers. Other parameters including relative surface dose (Ds), depth of maximum dose (Dmax), PDD at 10 cm, beam flatness, penumbra are also analyzed to study the volume averaging effect.

Result and Discussion: Preliminary analysis shows good results for smallest volume ion chamber that is Pin-Point chamber. The analysis with other chambers is in progress using all available photon energies.

The detailed results will be presented in full paper.

   P-91: Treatment Time Reduction with the Use of a Three Dimensional Printed Electron Beam Modifier for Total Skin Electron Treatments Top

S. Diamantopoulos, I. Kagkiouzis, G. Patatoukas, M. Dilvoi, E. Kipraiou, V. Kouloulias, E. Efstathopoulos, K. Platoni

Department of Radiology, Radiotherapy Unit, ATTIKON Hospital, University of Athens, Athens, Greece. E-mail: [email protected]

Introduction: Total Skin Electron Beam (TSEB) irradiation, is an effective treatment for skin malignancies. It is performed at an extended SSD, usually using two angled electron beams which create a large and homogenous field at treatment distance. Patients take successively six different positions to cover the entire skin. This procedure could be rather exhausting for the patients as it can last up to 30 min.

Objectives: The main objective of this work was to reduce treatment time and deliver the prescribed dose in a more comfortable way. Therefore, we tried to develop a variant of the already established six-dual field technique by creating a clinically acceptable single TSEB field.

Materials and Methods: To produce the single TSEB field various beam modifiers of different materials (aluminum and plastic) and shapes were tested. Utilizing 3D printing technology and the TSEB immobilization device of our department, thermoplastic modifiers were designed and constructed following a trial and error procedure. Electron beam characteristics were measured and calculated both at SSD=100 cm and at treatment level.

Results: The 3D printed modifier shaped the electron beam resulting to a clinically acceptable 6 MeV field of 176 cm x 70 cm field with 10% inhomogeneity in vertical and 3% in the lateral dimension with adequate skin coverage at SSD=400 cm. Underdosed areas do appear near the edge of the field, but in regions located far from the torso of the patient. Contaminating x-ray radiation is within clinically accepted levels (<5%).

Discussion: In general, aluminum scatterers of the same thickness, cause different modification according to the area of blocking. Smaller modifiers, cause proportionally smaller profile enlargement, in respect to the larger ones. With aluminum modifiers central dose deposition was reduced significantly and therefore MUs (and treatment time) should be increased in undesirable levels. On the other hand, plastic modifiers offer a good combination of field dimensions and treatment time. Furthermore, with 3D printing technology, they can be designed to produce the desired beam intensity at treatment plane.

The proposed modification of the original TSEB technique of our hospital could probably benefit mostly feeble patients who could not tolerate a thirty-minutes standing position without compromising the quality of their treatment.

   P-92: Evaluation of Effect on Output Factor in Customized Electron Fields Collimation in Radiotherapy for Various Energies Top

Mandvi Dixit, Anoop Kumar Srivastava, S. P. Mishra, S. Farzana, Soniya Pal, Madhup Rastogi, Rohini Khurana, Rahat Hadi, Kamal Sahni, Ajeet Gandhi, Shantanu Sapru

Department of Radiation Oncology, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India. E-mail: [email protected]

Introduction: Electrons are widely used in combination with photon beams or as standalone modality for radiotherapy with energy ranging from 4MeV-15MeV. The electron beams are applied using varies sizes of applicator with cutouts to match the tumor topology and conform to the clinical requirements. However, in routine clinical practices customized electron cutouts of cerrobend are prepared which may be circular, rectangular or of any other geometry to meet the need of the target volume. The electron cutouts in combination with applicators affect the output, PDD and other dosimetric parameters. It has been reported that the changes in beam characteristic of high energy and small cutouts are more profound due to lack of lateral scattering contribution. In this study it was propose to evaluate the dosimetric parameters of cutout and compare it with electron beam characteristics obtain from the various algorithm of the treatment planning system (TPS). The measured data and the TPS generated values have been compared to obtain the perturbation that may be induced in clinical practice. This study attempts to demonstrate that small cutout dosimetry in electron is critical when used as standard alone modality or in combination with photon beam abutment.

Objective: The objective of this study is to evaluate the correlation between the beams profiles obtains through direct measurement for cutouts with TPS generated values using various algorithms.

Materials and Methods: PTW dosimetry (PTW Freiburg, Germany) with Markus chamber was utilized for measurement. The circular applicators of dia 2 cm, 3 cm, 4 cm, 5 cm and rectangular and square cutouts of dimension 4×4, 6×4, 8×5.5, 10×6, 14×8, 14×12 were evaluate. The cutouts factor and other beam characteristics were measured using solid water phantom for the energy range of 4MeV, 6MeV, 10MeV, 12MeV on Elekta infinity Linac system. The parallel plate chamber model no-TM 23343-004309 having sensitive volume of 0.055cc was used and IAEA TRS-398 protocol was followed in this study. The dosimetry was performed at 100 cm SSD by using 10 × 10 cm2 applicator field size for standardization. The dosimetric patterns for circular, rectangular and other geometries were obtained and were normalized with respect to values for 10×10 cm2 applicator. The data obtained is detailed in [Table 1]a and [Table 1]b.
Table 1: Electron applicator output factors for 4 MeV, 6 MeV, 10 MeV, 12 MeV electron energies

Click here to view

Results and Discussion: It has been found that for applicator size 6 × 6 the TPS calculated values are higher at all energies than the measured values. However when large applicator of 14 × 14, 20 × 20, 25 × 25 were used the measured values for 4MeV, 6MeV are less than the calculated values. The observed variations have been found to be 4% to 17% for the cutout geometries evaluated. However for the larger applicators the calculated value from TPS for energy range of 10MeV, 12MeV are larger than the measured values. It is observe that for higher energies the calculated values by TPS always exceeds by the measured values. It can thus be concluded that pencil beam algorithm at higher energies for all sizes of applicator provided deviation than the measured values. The possible reason attributable to this aberration may be lack of lateral contribution of scattering. This study thus provides significant information that cutout factors for all fields which are customized to match the tumor topology should be independently measured and beam library thus accordingly prepared to obtain the dose profile in target volume. The resultant significant error may influence the clinical outcome if the TPS calculated values are utilized for routine dose calculation. It is essential to be careful in using the small cutout of the dia 2 cm to 4 cm where the deviation may be large enough to influence the dose homogeneity and clinical outcome. This aspect will be presented and discussed in detail.

   P-93: First Application of Hemi-Body Electron Beam Irradiation in Greece: Set Up, Measurements and Dosimetry Top

Platoni Kalliopi, Dilvoi Maria, Delinikolas Panagiotis, Patatoukas George, Kypraiou Eyfrosini, Kougioumtzopoulou Andromachi, Trogkanis Nikolaos, Gazouli Maria1, Efstathopoulos Efstathios, Kouloulias Vassilis

Department of Radiology, University General Hospital “ATTIKON”, School of Medicine, National and Kapodistrian University of Athens, 1Department of Basic Medical Science, Laboratory of Biology, School of Medicine, University of Athens, Athens, Greece. E-mail: [email protected]

Introduction: Half body (Hemi body) electron irradiation (HBIe-) aims to deal with cases of superficial skin tumors with more symptomatic density on upper or lower body. Resembling Total Skin Electron Beam Technique (TSEB), the spectrum of using HBIe- includes various deceases such as Kaposi's sarcoma and T-Cell Lymphoma plus its product diseases. An attempt for the first application of this external radiation therapy technique in Greece took place at the Radiation Therapy Unit of 2nd Department of Radiology of University of Athens at University General Hospital “ATTIKON”.

Objective: The purpose of this work is to present and to comment on the results of the first application of HBI electron beam irradiation in Greece. The procedure included amongst others, finding the proper beam angle for the lower torso, the deployment of a custom made shielding device for the upper torso, the appropriate positioning and immobilization of the patient's body and finally the dosimetric verification of this technique using thermo-luminescence dosimetry (TLDs), placed on the patient's skin.

Materials and Methods: The first patient, who treated with HBIe- technique, was male, 64 years old and had Kaposi's sarcoma, the disease was extended to the lower torso. HBIe- modality was developed on a linear accelerator VARIAN Clinac 2100C. To produce 6 MeV electron beams of field size 36 x 36 cm2, delivered at the high dose rate of 2500MU/min at isocenter, a single beam with its central axis pointing vertically to treatment plane (Gantry angle at 279.5 degrees for Lower HBIe-) at SSD 388 cm. The custom made chamber of our department, used for TSEB treatment was also utilized for HBIe-, providing appropriate conditions for skin irradiation (energy degradation of nominal 6MeV electron beams, field size widening through scattering and patient positioning). Irradiation procedure demands a standing patient that takes, in total, six treatment positions. For the Lower HBIe- case, a custom made universal shielding was attached to the treatment chamber. Any additional shielding for sensitive areas and/or organs at risk (eyes, nails, genitalia etc.) should be designed for each patient individually. Finally dose uniform delivery was monitoredusing thermo-luminescence dosimetry (TLDs).

Results: The treatment was dosimetrically monitored during his first two sessions. Patient dosimetry showed a very good agreement with the expected mean dose of 2Gy as mean patient dose was (1.7Gy). Furthermore, minimum and maximum values were at the level of 2.6Gy and 1.1Gy respectively. Spatial variations of the dose distribution can provide essential insights on the patient irradiation conditions and can assist vitally in the dosimetric optimization of the applied clinical protocol.

Discussion: Beam quality indexes and dosimetry aspects were defined with precision in order to provide an effective treatment. Every physical parameter was in agreement with suggested values of the international guidelines. In conclusion, hemi body electron irradiation can be implemented efficiently and with safety at the Radiation Therapy Unit of Athens University's General Hospital 'ATTIKON'.

   P-94: Quantitative Analysis of Prompt Gamma Ray Imaging During Proton Boron Fusion Therapy According to Boron Concentration Top

Han-Back Shin, Moo-Sub Kim, Sunmi Kim, Kyu Bom Kim1, Do-Kun Yoon, Hye Jeong Yang, Tae Suk Suh

Department of Biomedical Engineering, Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, 1Department of Electronic Engineering, Sogang University, Seoul, Korea. E-mail: [email protected]

Introduction: proton boron fusion therapy (PBFT) has been suggested as a novel radiation therapy technique and tumor monitoring technique for use during treatment. The PBFT method is a treatment technique based on the proton-boron fusion reaction. We confirmed the generation of a 719 keV prompt gamma ray after the proton-boron reaction. Thus, it was possible to develop a tumor-monitoring technique using a prompt gamma ray during PBFT. The main benefit of this prompt gamma ray imaging technique is a tumor monitoring method that does not require an extra dose during treatment, unlike computed tomography (CT) and X-ray. In our previous studies, a prompt gamma ray image was acquired with a specific boron concentration that was much higher than the clinically appropriate boron concentration range, so those studies were more conceptual in nature.

Objectives: The purpose of this study is to evaluate prompt gamma ray images during PBFT with Monte Carlo simulations using the boron concentrations allowable in clinical application. This study shows the effectiveness of the prompt gamma ray imaging technique during PBFT. It can be reflected to actual imaging techniques using boron compounds in clinical applications.

Materials and Methods: To acquire a prompt gamma ray image from 32 projections, we simulated four head single photon emission computed tomography and a proton beam nozzle using a Monte Carlo simulation. In addition, we used a modified ordered subset expectation maximization reconstruction algorithm with a graphic processing unit for fast image acquisition. The therapeutic conditions of PBFT included a low-energy proton beam and boron concentrations from 20 to 100 μg at intervals of 20 μg. For quantitative analysis of the prompt gamma ray image, we acquired an image profile drawn through two boron uptake regions (BURs) and calculated the contrast value, signal-to-noise ratio (SNR), and difference between the physical target volume and volume of the prompt gamma ray image.

Results and Discussion: The relative counts of prompt gamma rays were noticeably increased with increasing boron concentration. Although the intensities on the image profiles showed a similar tendency according to the boron concentration, the SNR and contrast value improved with increasing boron concentration. In addition, the difference between the physical target volume and prompt gamma ray image volume in each BUR decreased as the boron concentration increased.

Conclusion: We confirmed that the prompt gamma ray images depending on the boron concentration were successfully deducted during PBFT. This study suggests that a tumor monitoring technique using prompt gamma ray detection can be clinically applicable even if the boron concentration is relatively low.

   P-95: Development of Water Equivalent Multi-Layer Ionization Chamber with Liquid Crystal Polymer Top

Shigekazu Fukuda1, Hiroyuki Kobayashi1,2, Soma Iwata3

1National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, 2Graduate School of Science, Chiba University, 3Accelerator Engineering Corporation (AEC) Chiba, Japan. E-mail: [email protected]

The dose distribution of the therapeutic carbon beams, especially, the depth dose distribution (DDD) is important, because the physical DDD of SOBP that can be converted to the homogeneous DDD biologically and clinically is not homogeneous but become decreasing according to the depth from the surface. So we have developed the water equivalent multi-layer ionization chamber (W.E.MLIC) that enable us to measure the physical DDD at one time with the equivalent results obtained by scanning an ion chamber in the water phantom which it takes much longer time.

In the study we developed new prototype of W.E.MLIC with Liquid crystal polymer (LCP). In the last study we evaluated stability of W.E.MLIC which consisted of PMMA and cupper plates and we found the short-term and long-term instability of the output from MLIC. Furthermore, there were proved two possible causes of these instability problem. The first cause was the irradiation of the carbon beams to the readout patterns which conducted collected charge. The second cause was that signal substrate made from PMMA, which has hygroscopicity, could be shrunken in a different manner of the cupper plates in a dry environment and resulted in the sensitive volume decreasing.

On the base of these results, we improved the readout pattern whose width was narrower (from 0.5 mm to 0.1 mm). In addition, we adopted substrate made from LCP which has lower hygroscopicity instead PMMA and cupper plates. By using carbon beams of 400 Mev/n accelerated by HIMAC, we measured the water equivalent thickness of LCP and examined the water equivalence and stability of the new prototype of W.E.MLIC. We obtained the results that the water equivalence was good like previous studies and the stability of the output from the new W.E.MLIC with LCP was better than previous one.

   P-96: Temporal Changes of Target Volumes And Oar Volumes During High Precision Radiotherapy: A Prospective Study Top

Debojoyti Dhar, Saibal Mukherjee, Arundhuti Chakraborty, Liton Naha Biswas, Suman Mallik1, Jyotirup Goswami1, Akhter Jawade, Tanweer Shahid, Jibak Bhattacharya, Poopathi Venkataraman, Bipasha Pal1, P. Nagendran, Subhra Biswal, Pramod Yadav, SaubhikGhosh

Department of Oncology Radiation, Apollo Gleneagles Hospital, 1Department of Radiation Oncology, Narayana Superspeciality Hospital, Kolkata, West Bengal, India. E-mail: [email protected]

Introduction: Tumor shrinkage in response to radiotherapy, change in OAR (organ at risk) volume and weight loss may impact on the dose-distribution in both target and organ at risk (OAR) and hence the therapeutic outcome in patients with Head and Neck cancer. In this study, we investigated temporal changes of the target volumes and OAR volume during radiotherapy to adopt a strategy for adaptive radiotherapy.

Materials and Methods: Twenty-six patients who underwent radical chemo-radiotherapy (CTRT) for head and neck squamous cell carcinoma between April'12-April'13 were prospectively analyzed. After immobilization, Computed Tomography (CT) scans were taken from base of the skull to sternal angle using 3 mm slices by Siemens Somatom Emotion 16 slice CT scanner. Targets and OAR were contoured using Focal Sim. Treatment Planning was done on the XiO Treatment Planning System (ELEKTA AB, Sweden). All patients underwent 3D-CRT/IMRT. The prescription dose was 59.4 Gy-70Gy @ 1.8 -2Gy/fraction. All patients underwent a CT scan after 20 fractions. Targets and organs at risk were similarly outlined on these scans as above. The cranio-caudal dimensions of the planning target volume (PTV) were kept the same. Only the part of PTV going out of body contour (due to weight loss) was changed. Volume changes of targets and OARs were analyzed using SPSS 16.

Results: Comparison between both CT-scan (planning CT and CT at 20th fraction.) showed changes in GTV (mean 24.56cc Vs 19.86cc p<0.001, 95% CI 2.86-6.54), PTV (mean 280.44cc Vs 255.1cc p=0.48, 95% CI -3.36-6.93), right Parotid (mean 27.43cc Vs 22.25cc p<0.001, 95% CI 3.44-6.90) and left Parotid (mean 25.38cc Vs 20.97cc p<0.001, 95% CI 2.81-5.99) volumes as depicted in [Table 1].
Table 1: Variation in volume of GTV, PTV and Parotid

Click here to view

Discussion: Anatomical changes can occur during radiation therapy of head and neck cancer patients. This can lead to difference between planned and delivered dose. After 4-5 weeks of adjuvant chemo-radiotherapy, it is commonly found that there is reduction in body weight due to oral mucositis. As a result, there is a change in the patient's contour and the relative positions of the GTV/PTV and OARs may change. In the present study, we have found significant changes in GTV volume (p<0.001), and also change in OAR volume, which in this case is the parotid glands (p<0.001 for both left and right parotids). On the other hand, the total PTV volume has not been found to change significantly (p=0.48), since the PTV volume is over the entire neck-nodal region. However, for some patients we have found the PTV volume to extrude outside the body contour. Though the PTV volume does not change appreciably, our findings point to the need for re-planning after repeat CT scan, since some of the OAR's migrate near or away from the GTV due to change in both GTV as well as OAR volumes, and due to PTV extending beyond body. It is essential to re-plan to identify dosimetric changes and to ensure adequate doses to target volumes and safe doses to normal tissues.

Conclusion: Volumetric changes in the target volume and OARs were observed could have potential dosimetric impact when highly conformal treatment techniques are used. It Suggest that adaptive strategies, where patients are re-imaged and possibly replanned during treatment, are worth evaluating.

   P-97: Dosimetric Evaluation of Indigenously Developed Non Metallic Artifact Free CT Fiducial Marker Top

G. Kesavan, S. Senthilkumar1

Department of Radiotherapy, Vadamalayan Hospitals Pvt. Ltd., 1Department of Radiotherapy, Madurai Medical College, Govt. Rajaji Hospital, Madurai, Tamil Nadu, India. E-mail: [email protected]

Introduction: Fiducial markers are used in a wide range of medical imaging applications. Fiducial markers are commonly used above the patient surface in target region and serve as a reference. Ideally, the fiducial markers should be easily identified and clearly visible on simulation. Difficulty arises when marker creating artifacts in the CT image, and these artifacts affect the clarity of the anatomical region of interest. There is significant error in CT number due to bright and dark streaks. Thin bright and dark streaks originating from the metal based fiducial markers.

Objectives: Aim of this study was to discuss the dosimetric evaluation of the indigenously developed non-metallic artifact free CT fiducial and compare with the metallic CT fiducial during CT based planning.

Materials and Methods: We have used the newly developed non-metallic CT fiducial for our RT planning CT simulation for Ca. patients in different sites such as Brain, Head and Neck, Thorax, Abdomen and Pelvis and also with phantom. Previously we have used metallic based fiducial for our routine RT planning and used to found the streak artifacts. These type of artifacts seriously degrade the quality of CT images and sometimes to the point of making them diagnostically unusable and also create problem during auto-contouring. Thin bright and dark streaks originating from the metal based fiducial markers. Difficulty arises when marker creating artifacts in the CT image and these artifacts affect the clarity of the anatomical region of interest. There is significant error in CT number due to bright and dark streaks. We have used the metallic fiducial on the right side and non-metallic on left side of the patient during CT simulation based on the laser reference. The same method was adapted for other sites as well as phantom.

Results and Discussion: We have found that the metallic fiducial produce isodose shift below to the fiducial on the particular slice and no shift in the non-metallic fiducial. Both metallic and non-metallic markers appeared similar visibility on the CT image and non-metallic not produce any artifact when compared with the metallic fiducial. Non-metallic has the electron density of 2000 but commercially available marker has more than 9000. So, non-metallic fiducial can be used for regular CT simulation in all clinical situation for better treatment without isodose shift. We conclude that the newly fabricated CT fiducial gives better clinical outcome compared with metallic fiducial.

   P-98: Variations in Internal Target Volume of a Moving Lung Tumour: ANALYSIS of a Moving Phantom Using Four-Dimensional Computed Tomography Top

Arun Balakrishnan, S. Sriram Prasath, Raj Kumar Shrimali, Indranil Mallick, Sanjoy Chatterjee, Chandran Nallathambi, N. Arunai Nambiraj2, K. Senthilnathan1, P. Ramesh Babu1

Department of Radiation Oncology, Tata Medical Center, Kolkata, West Bengal, 1Department of Physics, School of Advanced Sciences, VIT University, 2Centre for Biomaterials, Cellular and Molecular Theranostics, VIT University, Vellore, Tamil Nadu, India. E-mail: [email protected]

Background: A typical Four-dimensional Computed Tomography (4DCT) for lung stereotactic body radiation therapy (SBRT) contains images captured through the whole breathing cycle divided into ten phase-bins. However, in practice, inconsistencies in the breathing pattern and duration prevails and could potentially result in phase errors.

Objective: To evaluate the probable variation in internal target volume (ITV) of a moving lung tumour during stereotactic body radiation therapy due to inconsistency in free breathing rate using a programmable Quasar Phantom and Four-Dimensional Computed Tomography (4DCT) and also to analyse the phase error after binning in the moving phantom.

Materials and Methods: A programmable motion Quasar phantom with 6 mm longitudinal displacement of a lung equivalent cedar cylinder insert containing off-set placed 2.5 cm diameter tumour density sphere as tumour and sine wave rotational mode with 1 cm amplitude platform with a 6-dot marker was used. Seconds per breath was set at four seconds. In CT machine, 1/10th of the breathing period read from the Real-time Position Management (RPM) console was fed as the cine time between images. Cine duration was set with one second added breathing period and inter-scan time was set as one second. The images were sorted into ten phases based on the temporal correlation between surface motion and data acquisition with Advantage Workstation. The results of GE Advantage 4D, binned ten phase images, maximum intensity projection (MIP) and average intensity projection (AIP) were imported into Varian Eclipse version 10.0. The percentage of phase error with respect to 4 s is shown in [Table 1]. From the MIP set, ITV (tumour sphere created elliptical volume) structure was created under -400 HU window width to estimate the volume (cc). The same procedure was repeated with a known error value of ±0.5 seconds in cine time between images and the whole procedure was repeated five times for consistency.
Table 1: Percentage of phase error with respect to 4 s (actual setting of SPB in phantom)

Click here to view

Results: The observed ITV variation was ≤-1.9% error and <2% maximum phase error than the actual 4DCT breathing period setting in the 10-bins 4DCT image protocol.

Conclusion: There is no significant error due to small averaging variations of breath period entered cine time between images during 4DCT imaging.

   P-99: Evaluation of Planning Target Volume Margin for Two Imaging Protocols Top

G. Muthu Krishnan, S. A. Yoganathan1, K. J. Maria Das1, D. Udayakumar1, C. S. Sureka, Shaleen Kumar1

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, 1Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India. E-mail: [email protected]

Purpose: Usually, two imaging protocols such as daily and weekly portal imaging are used to study the setup error. The purpose of this work was to evaluate the setup error and derive the PTV margin for the above two imaging protocols in brain and prostate cancer patients.

Methods: Ten patients of each brain and prostate cancer (implanted with gold seeds) were retrospectively included in this study. All the brain patients had a pair of orthogonal 2D MV portal images and bony matching was used to analyze the setup accuracy; where as the prostate patients had 2D kV images and the marker matching method was used to analyze the setup accuracy. Two type of setup errors were calculated; one using daily portal imaging and other using weekly (first three fractions and then weekly once) portal imaging. The planning target volume (PTV) margins were calculated (excluding rotational error) for the observed setup error based on Marcel Van Herk recipe.

Results: The PTV margins for brain cases based on daily imaging were 2.6 mm, 4.0 mm and 2.7 mm in medio-lateral, cranio-caudal and anterior-posterior direction respectively; where as the same for weekly imaging were 2.9 mm, 4.7 mm and 2.5 mm respectively. Similarly, PTV margins for prostate cases based on daily imaging were 11.1 mm, 16.5 mm and 11.7 mm in medio-lateral, cranio-caudal and anterior-posterior direction respectively; where as the same for weekly imaging were 10.5 mm, 15.4 mm and 11.4 mm respectively.

Conclusions: Daily and weekly imaging protocols did not show any considerable variation (less Than 1 mm) for deriving PTV margins. Therefore the weekly imaging protocol is adequate for determining the PTV margin; which would also result in relatively lesser imaging dose to the patient.

   P-100: Assessment Of Surface Dose Using Radiochromic Film (EBT3) In Chest Wall Radiotherapy with Superflab Top

Challapalli Srinivas, Dilson Lobo, P. Suman Kumar, Sourjya Banerjee, P. U. Saxena, Dinesh Pai

Department of Radiotherapy and Oncology, Kasturba Medical College and Hospital (An Associated Teaching Hospital of Manipal University), Mangalore, Karnataka, India. E-mail: [email protected]

Introduction: Radiotherapy is offered to the chest wall in post mastectomy patients to reduce the risk of loco regional recurrence. Tissue-equivalent materials are used as a bolus to provide dose build-up along the skin and superficial chest wall in order to adequately treat any residual disease out to the skin to the full prescription dose. Accurate skin dose assessment is essential to assure that it is sufficient, below the tolerance level.

Objectives: The aim of this study is to measure the surface doses using radiochromic film (EBT3) a) in a locally fabricated semi breast phantom and b) in post mastectomy patients (6Nos) undergoing three dimensional conformal radiotherapy (3DCRT) to the chest wall, with 5.0 mm Superflab TM gel bolus.

Materials and Methods: A locally fabricated semi breast phantom having lung equivalent insert made with cork material (density 0.28 gm/cc), simulating the actual treatment of post-mastectomy chest wall radiotherapy is taken. Surface dose measurements were taken using EBT3 film with 5.0 mm gel bolus in predefined fiducial regions and were to compare the planned ones in treatment planning system (TPS). Post-mastectomy patients (6Nos) undergoing 3DCRT planned for chest wall to a total prescription dose of 50 Gray in 25 fractions were undertaken for surface dose measurements. Treatments were given with 5.0 mm gel bolus during first 15 fractions followed by without bolus to the rest of 10 fractions as per institution protocol. Two sets (with and without placing the 5.0 mm gel bolus sheet on to the chest wall) of simulated computed tomography (CT) scans in treatment position were obtained, keeping fiducial markers (with a thin copper wire) at five different locations (median, central, lateral, superior and inferior) around the scar region of chest wall. Treatment plans were generated in Xio TPS to the first set of CT scans (having gel bolus) to a dose of 30 Gray in 15 fractions to the clinical target volume (chest wall) with tangential beams of 6MV photon beam. Field in field technique, and / or motorized wedge filter was used to homogenize the dose distribution in all plans. Radiochromic EBT3 film pieces (of dimension 2 cm x 2 cm) were placed at predefined fiducial marker locations of chest wall and surface doses were measured three times during the course treatment of bolus plan which were compared with the calculated ones in TPS. Skin toxicity was assessed in all patients as per National Cancer Institute Common Toxicity Criteria (NCI CTC).

Results: Twelve patients with mean age of 52.4 years were treated with 5 mm bolus on to the chest wall during first fifteen fractions of prescribed dose. The mean percentage of planned dose (standard deviation) for median, central lateral, superior and inferior from EBT3 films were 101.1% (4.6%), 105.1% (6.3%), 97.1% (5.6%), 103.6% (6.3%), and 105.3% (4.6%) respectively. Three out of six patients experienced a maximum acute NCI CTC skin toxicity score of 2. There were no grade 3 and 4 toxicities.

Discussion: Chest wall radiotherapy with SuperflabTM gel bolus of thickness 5.0 mm is a feasible regimen during first fifteen fractions of total prescribed dose with acceptable dose build-up and skin toxicity in post-mastectomy patients.

   P-101: Medical Proton/Carbon Dosimetry Using Optically Stimulated Luminescence From Easily Prepared KCL: SM3+ Nanophosphor Top

Mini Agarwal, K Asokan1, Pratik Kumar

Medical Physics Unit, AIIMS, IRCH, 1Inter-University Accelerator Centre, New Delhi, India. E-mail: [email protected]

Optically Stimulated Luminescence (OSL) radiation dosimetry is widely used nowadays for the measurement of radiation dose in various field including industry, agriculture, research, space and medicine. All present OSL phosphors suffer one or other lacuna prompting us to synthesizes KCl:Sm nano phosphor which promises to be a cheap, easy to manufacture and have the capability to measure small and large radiation dose simultaneously with extraordinary efficiency. All the present OSL phosphors tend to saturate at higher doses (≈ 5-10 Gy) if they are able to measure small doses (≈ 1μGy). However, KCl:Sm nano phosphor defies this and can measure doses from 100 mGy to 1000 Gy with a linear response due to the incorporation of trivalent Sm3+ as stable defects. We prepared KCl:Sm by high-temperature solid-state synthesis method and optimized the concentration of Sm of 0.45%. We further investigated its promising use for medical carbon and proton dosimetry. We investigated optically stimulated luminescence (OSL) from KCl:Sm (0.45%) phosphor, potentially can be used for heavy ion radiotherapy (carbon ion heavier than protons). The OSL and TL just after OSL were recorded with irradiation of 500 keV proton and carbon ion beam with different fluences from 1 x 1013 to 6.25 x 1015. The OSL decay response of low-LET protons was found to very significant at a fluence of 2.5 x 1014 ions/cm2 than that observed for a high LET carbon ion beam. At at a fluence of 2.5 x 1014 ions/cm2, the luminescence efficiency of high LET was decreased about 65%. While for higher fluence 6.25 x 1015 ions/cm2, we observed a significant decrease in the luminescence efficiency with low LET protons about 70% than that was observed for high LET carbon ion beam. The ease of its preparation is striking and likely to be quite cheaper OSL phosphor than the later.

Application No: IS0018

   P-102: Extended Cone Beam CT Localization for Adaptive Radiotherapy and Dosimetric Evaluation of Kilovoltage Imaging Top

K. Mohamathu Rafic, Ebenezer Suman Babu, Timothy Peace Balasingh, B. Paul Ravindran

Department of Radiotherapy, Christian Medical College, Vellore, Tamil Nadu, India. E-mail: [email protected]

Introduction: Several authors have reported the practicability of computing dose calculation on CBCT images while addressing HU inaccuracies with appropriate scatter rejection and HU correction strategies. The off-centred detector panel arrangement in half-fan (HF) acquisition geometry of the OBI system limits the longitudinal coverage to a mere 16 cm with a maximum reconstruction diameter of 45 cm. However, in most clinical scenarios, the craniocaudal scanning length of CBCT is found to be inadequate for localizing the planning target volumes (PTV) with extended nodal coverage.

Objective: To develop extended tomographic localization and adaptive dose calculation strategies using HU corrected CBCT with an intention to overcome the limitation encountered in adaptive radiotherapy (ART) and explore dosimetric evaluation of kilovoltage (kV) imaging.

Materials and Methods: Planning CT (pCT) images of the Rando phantom (T12-to-midthigh) were acquired with pelvic-protocol using Biograph CT-scanner. Similarly, half-fan (HF) CBCT were acquired with fixed parameters using Clinac2100C/D linear accelerator integrated with on-board imager with 2-longitudinal positions of the table. For extended localization and dose calculation, two stitching strategies viz., one with “penumbral-overlap”(S1) and the other with “no-overlap”(S2) and a local HU -correction technique were performed using custom-developed Matlab scripts. Fluence modulated treatment plans computed on pCT were mapped with stitched CBCT and the dosimetric analyses such as dose-profile comparison, 3D-gamma (g) evaluation and dose-volume histogram (DVH) comparisons were performed. Daily imaging dose from pre-treatment CBCT procedure has traditionally been ignored. Hence, planar dosimetry for kV CBCT imaging and the penumbral dose overlaps resulting from proposed S1 and S2 strategies was performed using Octavius 1500 ionization chamber array.

Results and Discussion: The scanning length of CBCT was extended by up to 16 cm in S2 when the couch shift 'D' was equal to 'l' of single HF-CBCT acquisition geometry. On the other hand, S1 protocol resulted in an extended scan length of 15 cm with an overlap (n = 1 cm). The structures mapped from pCT to stitched CBCT (sCBCT) resulted in minor variations in the volumes of all the five structures. The treatment plans computed on the pCT when mapped onto the registered sCBCT resulted in small disparity in beam centre co-ordinates. The possible causes of this variation could be due to minor mismatch in registration, small differences in reconstruction diameter and the position of the center of mass of target volume. Both the strategies showed good match in the entire range of dose profile with respect to pCT, especially in the regions where the penumbral overlap and stitching were performed. Furthermore, the 3D g-evaluation technique used in the present study would serve as effective quality assurance tool for comparing the pCT and sCBCT based treatment plans with high spatial resolution dose distributions generated in the Eclipse TPS. We observed that the 3D g-evaluation results showed superior pass rate with more than 97.5% dose pixels passing both the g-criteria. In addition, HF-CBCT imaging resulted in 6 - 7.5 cGy peripheral dose contribution overall. Absolute dose measured using Octavius 1500 array at the regions of penumbral overlap of S2 was found to be relatively less compared to S1 strategy due to 1 cm overlap which can be reduced by selecting optimum 'n' value. Due to the lateral scattering of kV beam, S2 protocol also showed non-uniform dose at the penumbral region.

Conclusion: CBCT image stitching and HU-correction strategies were developed in our study to facilitate extended localization of target and normal tissues and accurate dose calculation. This enables routine adaptive replanning and reoptimization of treatment plans based on setup verification CBCT while circumventing the need for repeated planning CT that is a requisite for conventional adaptive radiotherapy.

   P-103: The Mathematical Methods of Proton Beams Modeling in the Treatment Planning System Top

Kunihiko Tateoka, Yuya Azuma, Yasuhiro Hasegawa, Keiji Nakazato, Ayaka Kikuchi, Hyuga Nireki, Masaru Takagi, Masato Hareyama

Proton Treatment Center, Sapporo Teishinkai Hospital, Sapporo, Japan. E-mail: [email protected]

Proton therapy system in Sapporo Teishinkai Hospital (Hokkaido, Japan) consists of a cyclotron (P235, Sumitomo Heavy Industries, Ltd.), an in-room CT (SOMATOM Definition AS), Oncology Information System (Mosaiq, Elekta) and Treatment Planning System (TPS) (Eclipse Protons ver.13.7, Varian Medical Systems, Inc).

Our facility has a multi-purpose nozzle which can irradiate both wobbler beam and scanning beam.

The commissioning for proton therapy with wobbler beam started from the summer of 2016.

In our TPS, a depth dose curve of a range-modulated proton beam with Ridge Filter is reproduced by weighting depth dose curves of mono-energetic beams with several ranges, and users must determine these weights for mono-energetic beam by hand. In order to determine these weights efficiently, two mathematical methods are used; one is the least squares method, and the other is the generalized reduced gradient method (it is built in Windows Excel solver tool).

γ-value (2% 2 mm) between TPS calculation and measurement data is required to pass in all depth region with reference conditions for modeling of a range-modulated proton beam. TPS calculations with different beam parameters (various energies, snout positions and field sizes) are compared to the beam data with the same parameters. In most cases, TPS calculations are consistent to the beam data with acceptable error but measurement data tends to be higher than TPS calculation in the plateau region of depth dose curve for the case that the field size is relatively small (40 mm × 40 mm at the isocenter).

In this presentation, performance of the two mathematical methods and the results of modeling for depth dose curves of range-modulated beams in our facility are reported. Furthermore, the difference of the depth dose curve for small field case is also discussed.

   P-104: On The Dosimetric Behavior of VMAT Plans with Respect to Various Photons Beam (FF) Energy Using Monte Carlo Dose Calculation for Carcinoma Cervix Top

N. Munirathinam, Pawaskar, S. H. Pawar, C. D. Lokahande

Department of Medical Physics, Centre for Interdisciplinary Research, D. Y. Patil University, Kolhapur, Maharashtra, India. E-mail: [email protected]

This study was designed to evaluate the Plan quality (TCP and NTCP), Conformity index (CI), Heterogeneity index (HI), treatment planning time, total MU and estimated treatment delivery time with respect to different Photon energy (6, 10 and 15 MV) VMAT plans are created for cervix tumor and the ultimate goal is provide an efficient photon energy for VMAT planning for Carcinoma Cervix.

Methods: A total of 10 Cervix case used for the study. All the plans are made with full single- arc for different Photon energy namely 6, 10 and 15 MV with default 180 control points using Monaco™ (Elekta Medical Systems, Crawley, UK) treatment planning system. The photon dose calculation is done by using a Monte Carlo algorithm. The dosimetrics such as PTV coverage, organ-at-risk sparing, Conformity index (CI), Heterogeneity index (HI), integral dose, treatment planning time, MU and minimum/maximum/mean doses are evaluated. The VMAT plans were delivered using an Elekta Versa HD linear accelerator with 160 MLC; the treatment delivery parameters such as the total MUs and delivery time from different increment size plans are compared.

Results: Our results show a comparable coverage of planning target volume (PTV) and OARs sparing CI and HI for all three energies; The numbers of MUs were 14.2 ± 1.6% and 19.2 ± 1.8% higher and IDs. Based on this study, 6 MV photon beam is a good choice for VMAT planning in case of cervix carcinoma, as it does not deliver additional exposure to patients caused by photo neutrons produced in high energy beams.

Conclusions: We compared different Photon beam energy VMAT plans and we found that 6 MV beam is dosimetrically better in comparison to 10 and 15 MV for Carcinoma Cervix as it produces a highly conformal, homogeneous plan with superior target coverage and better OAR sparing.

   P-105: Out OFF Field Photoneutron Spectrum Determination on the Patient Body Surface During Radiotherapy with High Energy X Rays Using CR 39 Films Top

K. R. Rajesh, R. Ganapathi Raman1, Naiby Joseph2, M. V Dheepthi2, Biju P. Thomas, N. M. Salim Sha

Department of Radiation Oncology, Caritas Hospital, Kottayam, 2Department of Physics, University of Calicut, Malappuram, Kerala, 1Department of Physics, Noorul Islam University, Kanyakumari, Tamil Nadu, India. E-mail: [email protected]

Introduction: The photoneutron spectrum at different locations of the patient body surface during radiotherapy is determined by using CR 39 film. CR 39 films are placed at different locations of the patient body surface and individual field neutron fluence is determined by placing separate CR 39 films for each field. The films are then etched with 6N NaOH at 70°C for 6 hrs. Then the films are imaged with a microscope with recording ability. The tracks in the films are then counted and the parameters required for the recoil proton energy calculation are determined by using a programme TRIAC II written in MathLab. Then the neutron energy is calculated from this recoil proton energy by applying the required calibration factors. Then the spectrum is determined and plotted using GNU plot. The main reaction channels responsible for the photoneutron production are identified.

Photoneutron production during radiotherapy treatment is a major concern when considering its high LET nature. Photoneutrons are mainly produced from machine head, air and from the patient itself by the (gamma, neutron) reaction. The scattering of photoneutron causes dose deposition to the critical organs far away from the treatment site. This may cause secondary cancer induction in the future. The present treatment calculation algorithms are not taking care about this photoneutron dose. The present study is focusing on the photoneutron production from the patient body only.

Materials and Methods: 15 MV X rays from Siemens Primus Plus linear accelerator is used for this study. CR 39 films with size 1 x 1 cm2 is used as the detector. The patients are classified based on the treatment site as pelvic, abdomen and thoracic cases. During the treatment delivery CR 39 films are placed at different locations of the patient body surface with respect to the isocenter in order to get the scattering dose to other normal areas. Each field is delivered separately and films are replaced field by field in order to get information from each field. The films are then tagged properly and taken for chemical etching. The chemical etching with 6N NaOH solution at 70°C for 6 hrs is done and the tracks are visualised with a microscope with a recording capability.

The images are then subject to automatic counting using the TRIAC II, a Math Lab programme. The output in the excel format gives information about major axis, minor axis and angle of recoil. From this data and using a calibration graph the recoil proton energy is calculated. Then the photoneutron energy is calculated by using the equation En = Ep/cos2 q. Then the energy is corrected for crossection (using EXFOR ENDF) and efficiency, and is binned in to separate intervals. Then the spectrum is generated using GnuPlot. By knowing the Q value for each reaction separate reaction channels can be identified.

Results and Discussion: The out off field photoneutron spectrum on the patient surface is determined for different treatment sites. The result shows significant amount of photoneutron fluence that are produced by the interaction of photons with various body elements (isotopes of C, H, N, O etc). Later this fluence can be given as an input to one of the simulation programme like Geant4 and hence the dose can be calculated. The result shows significant amount of photoneutron dose which has to give prime importance while considering the biological effects and secondary cancer induction.

   P-106: Impact Of CT Number Calibration Error in Radiotherapy Treatment Planning System Top

M. Nakao1, S. Ozawa1,2, K. Yamada1, K. Yogo1, F. Hosono1, M. Hayata1, K. Miki2, T. Nakashima3, Y. Ochi3, D. Kawahara3, Y. Morimoto4, T. Yoshizaki5, H. Nozaki6, K. Habara6, Y. Nagata1,2

1Hiroshima High-Precision Radiotherapy Cancer Center, 2Department of Radiation Oncology, Institute of Biomedical and Health Science, Hiroshima University, 3Department of Clinical Support, Hiroshima University Hospital, 4Department of Radiology, Hiroshima Prefectural Hospital, 5Department of Radiation Therapy, Hiroshima City Hiroshima Citizens Hospital, 6Division of Radiology, Hiroshima Red Cross Hospital and Atomic-bomb Survivors Hospital, Hiroshima, Japan. E-mail: [email protected]

Introduction: The accuracy of computed tomography (CT) number calibration is a key component for dose calculations in an inhomogeneous medium. There are two types of CT calibrations in radiotherapy treatment planning systems (RTPSs) for external photon beam radiotherapy; one is CT to relative electron density (CT-ED) calibration and another is CT to mass density (CT-MD) calibration. In a previous work, tolerance levels of only CT-ED calibration were reported, and it was shown that the tolerance levels of CT-ED calibration became stricter with an increase in tissue thickness and decrease in the effective energy of a photon beam. For the last decade, a low effective energy photon beam (e.g. flattening-filter-free (FFF)) has been used in clinical sites. However, its tolerance levels for CT-ED and CT-MD calibrations have not been established yet.

Objectives: The purpose of this study was to establish tolerance levels of CT-ED and CT-MD calibration for each tissue type with an FFF beam used in treatment planning.

Materials and Methods: The tolerance levels were calculated using the tissue maximum ratio (TMR) and each corresponding maximum tissue thickness. To determine tolerance levels of CT-ED calibration, TMR data from a Varian accelerator and the adult reference computational phantom data in the International Commission on Radiological Protection publication 110 (ICRP-110 phantom) were used in this study. The 52 tissue components of the ICRP-110 phantom were classified by mass density as 5 tissues groups including lung, adipose/muscle, cartilage/spongy- bone, cortical bone, and tooth tissue. The CT-ED calibration tolerance level of each tissue group was calculated when the relative dose error to local dose reached 2%. In addition, averaged electron density and averaged mass density were calculated for 5 tissues groups with ICRP-110 phantom, and 5 proportionality factors were calculated for each tissues group. The tolerance levels of CT-MD calibration was converted from the tolerance levels of CT-ED calibration with above proportionality factors.

Results and Discussion: The CT-ED calibration tolerance levels of a 6 MVFFF beam for lung, adipose/muscle, and cartilage/spongy-bone were ±0.044, ±0.022, and ±0.044, respectively. The thicknesses of the cortical bone and tooth groups were too small to define the tolerance levels. The CT-MD calibration tolerance levels of a 6 MVFFF beam for lung, adipose/muscle, and cartilage/spongy-bone were ±0.045, ±0.022, and ±0.045, respectively. Because the tolerance levels are stricter with a decrease in the effective energy of the photon beam, the tolerance levels are determined by the lowest effective energy in useable beams for radiotherapy treatment planning systems.

   P-107: Dosimetric Evaluation of Heart Dose Using Indigenously Fabricated Bee-Wax Phantom in the Treatment of Oesophageal Cancer Top

T. Suresh

Department of Radiation Oncology, Bharath Hospital and Institute of Oncology, Mysore, Karnataka, India. E-mail: [email protected]

Radiotherapy affects both tumor cells and normal cells. The estimation of absorbed dose to the nearby Organs-at-Risk (OAR) in the IMRT treatment is essential. In-vitro dosimetric verification prior to patient treatment has a key role in accurate and precision radiotherapy treatment delivery. The aim of this study is to determine the absorbed dose to the heart in the treatment of Carcinoma Oesophagus based on the TPS calculation and direct measurements on the wax phantom. Ten Oesophagus cases were planned using Eclipse TPS. All the measurements were carried out on Siemens Primus Plus Linac with indigenously fabricated 'Bee-wax' Thoracic phantom. The dose is measured using 0.6cc ionisation chamber with PTW UNIDOS E electrometer. Ion chamber is fixed in the cavity at center of the phantom with its longitudinal axis perpendicular to the direction of the beam. 1.25 mm thickness CT slices of phantom were imported on TPS Eclipse version 13.6. The various plans already done for actual patients were imported on phantom and dose was calculated using anisotropic analytical algorithm version 13.07.16 with 2.5 mm grid size. Verification plan was created for each patient plan on to the wax phantom. The dose was calculated at the position of the heart, at a depth of 7 cm from the surface of wax phantom. The IMRT verification plans were delivered by Linac with dynamic dose delivery technique and doses were measured and compared with doses planned on TPS. The variation between planned and measured dose were calculated and is found to be within the tolerance limit (less than ±3%) as prescribed by ICRU 83. The percentage of variation measured in the wax phantom is slightly high for certain cases which might be due to high gradient dose distribution nature of IMRT and lack of lateral electronic equilibrium for small field. The electron density of water and bee wax are almost similar, and using the mentioned bees wax phantom was a good choice for primary study.

   P-108: Relation Between Composite and Individual Beam IMRT QA Top

Pooja Moundekar, V. K. Sathiyanarayanan, Amit Nirhali, S. Mithun, Basu Sumit, Bhooshan Zade

Department of Radiation Oncology, Ruby Hall Clinic, Pune, Maharashtra, India. E-mail: [email protected]

Aim: The purpose of the study is to find the relation between the composite and individual beam fluence gamma passing rate in a patient specific IMRT QA.

Background: IMRT has been implemented in most of the centers across the country. The proximity of the critical structure to the tumor leads to a very complex dose distribution with steep dose gradient justifying IMRT QA. The 3% dose and 3 mm distance to agreement is the most widely used criteria for accepting the IMRT QA. But not always this passing criteria is full filled and some plans fail with a very bad %gamma and it usually leads to repeating the QA. In this study gamma analysis for each beam is done separately and tried to find whether or not the gamma passing of individual beam plays some role in composite gamma passing rate.

Methods: The patient specific IMRT QA was performed using Siemens Oncor Impression LINAC with 82 leaf OPTIFOCUS MLC with 1 cm leaf width. The IMRT plan was executed on Iba's IMatrix with actual gantry and couch angles. 15 IMRT plans were selected for whom the IMRT QA gamma passing rate defined by 3%/3 mm criteria for composite plan were below 90%. For these plans individual beam analysis was performed. Comparison was done between the average of individual beam and the composite fluence gamma passing rate.

Results and Discussion: The comparison showed a large variation in the percentage difference between the average of the individual beam and the composite fluence gamma passing rate varying from as low as 0.65% to 61%.

It was observed that for the plans for which the composite fluence gamma passing rate was very low had one or more beam with very low gamma passing rate and for majority of such cases these beams being dead lateral i.e. gantry 90° or/and 270° or for beam angles very close to lateral angles. This could be consequence of combination of several things like effect of gravity at gantry angles closer to 90°/270°, positional inaccuracy of MLC's, angular dependency of response of IMatrix etc; which we assumed to get diluted due to averaging effect from all gantry angles. Also further study needs to be carried out using film dosimetry to include the effect of spatial resolution of the detectors.

It was also observed that for some IMRT plans, the individual beam gamma passing rate for every beam was above 90% and still the composite gamma passing rate was below 90%. From this, we can infer that the direct averaging of the individual beam gamma passing rate and the composite beam gamma passing rate are not related linearly and needs to be studied further.

Conclusion: For majority of the IMRT plans for which the composite gamma passing rate was very low either had lateral beam angles or angles very close to them indicating the gravity effect acting on the MLC's at such angles, which may be machine specific in addition to the angular dependency of the IMatrix response and thus justifying the low gamma passing rate.

The composite gamma passing rate and the individual beam gamma passing rate were compared and it was found that average of the individual beam gamma passing rate is not linearly related to the composite gamma passing rate and this relation needs to be studied further.

   P-109: Efficacy of EPIQA in quality assurance of rapidarc –Our Institutional experience Top

S. Vendhan1,2, R. Murali2, N. Arunai Nambiraj3, S. Dhivya1, K. Ganapathy1, S. Saraswathi Chitra1, V. Murali1

1Department of Radiation Oncology, Apollo Cancer Institute, Chennai, 2Department of Physics, School of Advanced Sciences, VIT University, 3Centre for Biomaterials, Cellular and Molecular Theranostics, VIT University, Vellore, Tamil Nadu, India. E-mail: [email protected]

Introduction: EPIQATM (EPIdos, Slovak Republic) is a QA software that allows to convert a dosimetric image acquired by an Electronic Portal Imaging Device (EPID) into a dose map in water using Generalized Linear Algorithm for amorphous silicon (GLAaS) and to compare the dose map with a reference dose distribution from TPS. The GLAaS derives calibration factors for EPID's pixels using empirically measured dataset.

Objective: To evaluate the effectiveness of EPIQA in quality assurance (QA) of Rapidarc treatment plans.

Materials and Methods: For the purpose of EPIQA commissioning, set of dosimetric EPID images for open and transmitted fields of different field sizes are acquired for energies 6X and 10X. The acquired images along with output factor table using ionization chamber in a water phantom are fed into EPIQA to configure GLAaS algorithm parameter data file. This parameter data file is specific to individual linac and EPID for each energy.

Dosimetric images are acquired at isocenter plane with aS1000 EPID for twenty Rapidarc QA treatment plans delivered at Truebeam STx linac equipped with HD120 MLC. The acquired dosimetric images were used independently in EPIQA and Portal DosimetryTM (Varian Medical Systems, Palo Alto) workspace for QA analysis as shown in [Figure 1]. For rapidarc plans, portal dosimetry QA using Portal Dose Image Prediction (PDIP) algorithm is the established standard practice at our institute. The actual treatment plan, reference dose distribution calculated at recommended geometry and EPID acquired dosimetric images exported from Eclipse TPS to EPIQA for analysis. The 2D dose map generated by GLAaS from acquired image is compared with AAA calculated reference dose map where as in portal dosimetry, the acquired image is compared directly with predicted image by PDIP.
Figure 1: Ananlysis in portal dosimetry and EPIQA

Click here to view

For both EPIQA and portal dosimetry standard 3 mm/3% (DTA/DD) gamma tools were used with area gamma (g<1) as pass acceptance criteria for ≥95% analysed points.

Results and Discussion: Acquired portal image for all QA plans were individually analysed in EPIQA software and portal dosimetry workspace. Gamma analysis of all QA plans in EPIQA results in a minimum and mean area gamma<1 value of 95.2% and 98.1±1.5% respectively. A minimum and mean area gamma<1 value of 96.7% and 98.5±0.8% resulted in portal dosimetry.

Portal dosimetry verification is an integral part of patient database and an easy tool to execute and verify. The similar results of EPIQA software being an external third party verification tool gave more confidence on our existing QA verification system. In addition, EPIQA provides separate modules for machine QA and TPS QA which offers a valuable support in a busy radiation therapy department.

   P-110: Effect of Lead Foil on Electron Contamiation to Photon Beam Quality Index: Experimental And Monte Carlo Study Top

A. S. Jagtap, Nitin R. Kakade1, B. J. Patil2, S. D. Sharma1, S. D. Dhole

Department of Physics, Savitribai Phule Pune University, 2Department of Physics,, Abasaheb Garware College, Pune, 1Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: The photon beam quality index must be specified in order to determine the correct value of the beam quality conversion factor, k Q. For the calibration of photon and electron beams, AAPM TG-51 and IAEA TRS-398 protocols are commonly used by radiotherapy centres globally. These dosimetry protocols are based on absorbed dose to water calibration of the recommended ionization chambers. Tissue Phantom Ratio (TPR20/10) and percentage Depth Dose at 10 cm depth in water (%dd (10)x) due to photons excluding electron contamination are the recommended beam quality index in TRS-398 and TG-51 respectively. TG-51 protocol recommends to specify the photon beam quality for beams with energy 10 MV or above by measuring the value of %dd (10)Pb with a 1 mm lead foil positioned in the path of the beam to reduce the effects of the electron contamination from the accelerator to a negligible level. The quantification of electron contribution due to presence of lead foil will enhance the confidence for safe delivery of radiation dose to patient.

Objectives: To estimate the effect of lead foil on the contribution of electron contamination for 15 MV photon beam using TG-51 protocol, both experimentally and by Monte Carlo (MC) simulation. Also, to estimate beam quality index using TRS-398 and TG-51 protocol with Monte Carlo method.

Materials and Methods: The Varian Clinac iX medical linear accelerator equipped with 6 and 15 MV photon beams was used in this study. The PDD was measured for field size 10×10 cm2 using 0.13 cc cylindrical ionization chamber in 48×48×45 cm3 water phantom for 6 and 15 MV x-rays. In case of 15 MV photon beam, the lead foil of thickness 1 mm was used to measure beam quality according to TG-51 protocol. Moreover, the accelerator was modelled using the EGSnrc based BEAMnrc user code. The percentage depth dose (PDD) was estimated for 6 and 15 MV photon beams at source to surface distance of 100 cm. For the case of 15 MV PD D was also estimated by keeping 1 mm thick lead in the path of beam. The particle histories of 2×108 were simulated to achieve required statistical accuracy less than ±1%.

Results and Discussion: The measured and MC simulated PDD values for 10×10 cm2 field of 6 and 15 MV photon beams are well within ±1%. The comparison of beam quality index using TRS-398 and MC simulation are found to be 0.89% and 1.7% for 6 and 15 MV photon beams respectively. The percentage depth dose at 10 cm depth estimated by MC simulation for 15 MV photon beam with lead and without lead foil is within ±0.1% with the measurement. It has been observed that the contribution of electron contamination in 15 MV photon beam is reduced in the build-up region due to insertion of 1 mm lead foil. The calculated PDD of 15 MV photon beam for 10×10 cm2 field size at SSD 100 cm with and without 1 mm lead foil shows that the contribution of electron contamination is nearly negligible after 4 cm depth. It is concluded that the Monte Carlo simulation gives the accurate estimation of effect of lead foil used by TG-51 protocol. Moreover, the beam quality index measured by TRS-398 and TG-51 is matching well with Monte Carlo simulation.

   P-111: Novel Precise Measurement Method of Gamma Knife Perfection Irradiation Time Top

Takashi Aizawa, Koji Sasaki1, Emiko Fujii2, Kenji Taguchi, Noriyuki Kasai3, Naoto Yanagisawa3

Aizawa Health Checkup Center, Matsumoto, 1Department of Radiation Therapy Education and Research, Gunma Prefectural College of Health Sciences, Graduate School of Radiological Technology, Maebashi, 2Department of Pediatrics, Takamatsu Red Cross Hospital, Takamatsu, 3Aizawa Hospital, Matsumoto, Japan. E-mail: [email protected]

Introduction: Gamma knife quality assurance guideline was issued by the Japanese Leksell Gamma Knife Society in Japan, but there is no description concerning the measurement of the irradiation time, and is not measured even by the manufacturer's inspection.

Objective: To devise a new highly accurate irradiation time measurement method and to examine its measurement accuracy.

Materials and Methods: The spherical phantom which attached to the gamma knife was installed in the movable couch and the dosimeter (PTW Freiburg TN 31010) was inserted into the spherical phantom. Then we measured irradiation time using the electrometer (TomoElectrometer; Standard Imaging) which could measure it over time. The irradiation time was calculated from the FWHM of the rising part and the falling part at a curved line of the measurement data, and the difference from the set irradiation time was measured as an error.

Results and Discussion: By using an electrometer that can measure at a sampling interval of approximately 200 ms, it becomes possible to precisely measure the irradiation time of the gamma knife. The irradiation time tended for each collimator, and it was found that there was an error of about -200 ms at 4 mm, about -40 ms at 8 mm, and about 90 ms at 16 mm. Even if the irradiation time was changed, the error was similar. Since each sector is synchronized, the difference between one sector measurement and all sector measurements is small. We have devised a new precise measurement method of gamma knife perfection irradiation time and confirmed that the irradiation time error is reproducible. By staying in control of the inherent error value for each collimator diameter, quality control by the user can be easily performed.

   P-112: Comparison of Beam Characteristics for Fixed and IRIS Collimators of M6 FI+ Cyberknife® System Top

M. Kannan, J. Ninan, P. Chandrasenan, H. Kaur, K. Verma, S. Goel, S. C. Pande

Department of Radiation Oncology, Artemis Hospital, Gurgaon, Haryana, India. E-mail: [email protected]

Introduction: The CYBERKNIFE® M6 FI+ unit has two collimator systems in which the IRISTM Variable Aperture Collimator is a computer-controlled collimator whereas the aperture of fixed collimators is static. The beam characteristics of CYBERKNIFE® vary with the configuration of the collimator.

Objective: We compared the beam characteristics of these two different collimators in M6 FI+ CYBERKNIFE® SYSTEM.

Materials and Methods: The PTW Diode E, PTW PinPoint 0.015 cm3, GAFchromicTM film (EBT3), PTW SCANLIFT MP3 RFA, IRIS QA software were used to procure data for beam characteristics of different aperture sizes. Statistical analysis was conducted to evaluate the difference between fixed collimator and IRISTM collimator.

Result and Discussion: The maximum relative error in aperture size was -6.8% for 5-mm collimator while the minimum relative error was -1.54% for 60-mm collimator. Output factor for fixed and IRISTM were compared with the Composite Data, the maximum relative error was 2% and 7.3% for 5-mm collimator using PTW Diode E. Same measurements were repeated using PTW PinPoint and the maximum relative error was -23.8% and -20.57% for 5-mm collimator. In PDD measurement, the Dmax increased with increase in aperture size up to 2.5 cm for both the collimators and beyond that, there was no difference in Dmax. Surface dose was less in IRISTM as compared to fixed collimator where the maximum relative error was -6.48% for 10 mm-collimator while the minimum relative error was -0.01% for 60-mm collimator. For both collimators, the penumbra increased with increase in aperture size. The maximum relative error was 28.7% and 32.8% for 60-mm collimator. Flatness and beam symmetry decreased with increase in aperture size for both the collimators.

   P-113: Evaluation of Half Value Layer and Total Filtration in Varian Truebeam KV-CBCT Top

C. Senthamil Selvan, C. S. Sureka, M. Vadivel1, A. Pichandi1

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, 1Department of Radiation Oncology, Bangalore Institute of Oncology, Bengaluru, Karnataka, India. E-mail: [email protected]

Introduction: The intensity of X-ray beam is an important property in kilovoltage cone beam computed tomography (kV-CBCT) for safety measures. In kilovoltage energy region, the half-value layer (HVL) is often used to describe the X-ray beam quality and characterize the effective energy by converting the HVL to the linear attenuation coefficient or mass attenuation coefficient. The HVL of a beam is the thickness of material required to reduce the intensity of an X-ray beam to one-half of its initial value. The total filtration (TF) of the beam includes the inherent and added filtration.

Objectives: To measure the half value layer and total filtration values of low kVp to high kVp in kilovoltage (kV) cone beam computed tomography (CBCT) using Nomex multimeter.

Materials and Methods: The Varian TrueBeam On-Board Imager (Varian Medical Systems, USA) and PTW-NOMEX multimeter (PTW-FREIBURG, Germany) were used to measure the output of the X-ray machines. Aluminium attenuators of 10 × 10 cm with thicknesses of 1 mm were used. The square shaped additional Al filter of more than 99.8% purity has been designed. The multimeter was positioned at 100 cm perpendicular to the X-ray tube. The first measurement was done without the aluminium attenuator. Next, the measurement was repeated with a 1 mm Al attenuator in place between the X-ray tube and the multimeter. The exposure was repeated with increasing the thickness of the aluminium in the order of 1 mm until the value approached the expected HVL value. The operating parameters were subsequently repeated for X-ray tube voltage in the range of 40 kVp to 140 kVp in 20 kVp intervals for the tube current of 100 mA and exposure time of 100 msec. In addition, a final exposure without an aluminium attenuator was repeated for every voltage to confirm the output stability.

Results and Discussion: From this study, it is measured that the averaged HVL value is 1.52 mm Al at 40 kVp and 5.83 mm Al at 140 kVp without any attenuator. With 1, 2 and 3 mm of Al, the HVL value is 1.68, 1.91 and 2.04 mm Al respectively at the lower tube voltage of 40 kVp. Similarly, at the higher X-ray tube voltage of 140 kVp, the HVL values are 6.45, 6.87, 7.28, 7.59, 7.86, 8.12 and 8.35 mm Al respectively. The measured total filtration value is 3.1 mm Al at 40 kVp, 2.7 mm Al at 80 kVp, 2.8 mm Al at 100 kVp, 120 kVp and 140 kVp without added attenuator. The measured total filtration value is 3.8 mm Al at 40 kVp, 3.3 mm Al at 80 kVp, 3.5 mm Al at 100 kVp, 3.6 mm Al at 120 kVp and 3.8 mm Al at 140 kVp with 1 mm Al. The measured total filtration value is 8 mm Al at 140 kVp with 7 mm Al etc. It is also found that these HVL and TF values are in good agreement with the International Electrotechnical Commission (IEC 2008) report, Food and Drug Administration (FDA) report, the American Association of Physicists in Medicine (AAPM) Report 08 and Atomic Energy Regulatory Board (AERB) report.

   P-114: Effect of Plastic Tray on the Photoneutron Dose Equivalent at the Isocenter and the Maze Entrance of Medical Linacs: A Monte Carlo Simulation Top

S. M. Hashemi Dizaji

Radiation Application Research School, Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran. E-mail: [email protected]

One of the important problems of using high energy linacs is the production of photoneutrons. Besides the clinically useful beam, high energy photon beam, medical linacs produce secondary neutrons. These phtoneutrons increase dose equivalent at the isocenter of medical linac. This causes the increase of the neutron shield thickness of the treatment room maze door. In this study, the effect of plastic tray on reduction of photoneutron dose equivalent produced by a high energy medical linac at patient plane and near the maze door is investigated by Monte Carlo simulation. To determine the photoneutron dose equivalent received by the isocenter and the maze door a simplified linac head simulated. A 1 cm thick tray defined near aperture of simplified linac head. The bunker defined as a typical treatment room with the walls made of standard concrete. Neutron detectors defined as 20 cm diameter spheres at isocenter and near the maze door. Four different situations were considered, one without tray and three others with tray. Simulation carried out by running the computer to produce 1 billion particles for each case. The results show that by inserting the plastic tray in the path of the X ray beam, the photoneutron dose equivalent at the isocenter was decreased obviously compared to open field. But there is not any change in photoneutron dose equivalent near the maze door. It may be concluded that using plastic tray, decreasing photoneutron dose equivalent at the isocenter, does not reduce the photoneutron dose equivalent at the vicinity of the maze door.

   P-115: An Investigation of Collimator Head Scatter with Columnar Miniphantom Top

S. Palit, B. Pal, S. Das, P. Sarkar

Department of Radiotherapy, Narayana Superspeciality Hospital, Kolkata, West Bengal, India. E-mail: [email protected]

Introduction: The initial reason for introducing output factor in air is for the determination of phantom scatter factor (Sp ). The most common method involves the measurement of the total scatter factor, Scp , in a phantom and the head-scatter factor output factor, Sc . The phantom scatter, Sp , is then calculated as Sp = Scp /Sc. AAPM Task Group 74 report recommends that build up caps with sufficient lateral and longitudinal thicknesses to eliminate electron contamination and maintain transient electron equilibrium, be used for the measurement of Sc . These are generally called as columnar miniphantoms.

Objectives: Our objective has been to measure head scatter factors for 6MV beam of Elekta Versa HD using high atomic number build up caps provided by the TPS vendor, and compare this with the same measurements using a water equivalent miniphantom fabricated in-house, made as per recommendation of AAPM Task Group 74. We have also included measurements of head scatter factors of unflattened (FFF) beams available in Versa HD for comparison with the same measurements for flattened (FF) beams.

Materials and Methods: The Versa HD Linac has Agility multileaf collimator with 160 leaves of projected width 0.5 cm at the isocenter. There are no backup collimators. Two different types of build up caps viz, made of brass and of PMMA were used to measure Sc . The brass build up caps were cylindrical, of wall thickness equivalent to dmax, the depth of maximum dose for a given energy. The density was 8.7 g/cc. The miniphantom had a density of1.16 g/cc and a radiological depth of 10 g/cm. The effect on Sc of varying SSD from 80 cm to 120 cm, for both types of build up caps was studied. The effect of wedges on Sc was investigated. The Sc was measured for the rectangular fields to check the collimator exchange effect. PTW 0.6cc chamber and Unidos electrometer were used for the measurements.

Results: A variation of Sc values of 2.2% was observed over the entire range of 4 x 4 cm2 to 40 x 40 cm2 field sizes for 6 MV-FFF. The SSD had no influence on head scatter for both flattened and unflattened beams. The Sc values with and without the wedge is compared in PMMA, and increases up to 5.2% in larger fields compared to without wedge. The collimator exchange effect reveals that the opening of upper jaw (MLC) increases the value of Sc and it is less significant in FFF beams. Sc is slightly higher (0.7%) with brass build-up cap than with PMMA mini phantom measured values, irrespective of 6MV-FB, 6MV-FFF. The Sc for 6MV-FB is lesser than the 6MV-FFF 5 x 5 cm2 field sizes, and a maximum deviation of Sc values is 3.8%. The Sc for 6MV-FB was higher than the 6MV-FFF in 40 x 40 cm2 field sizes, and a maximum deviation of Sc value was 1.6%. With the effect of collimator exchange, Sc values varied from 0.98% to 0.26% (6MV-FB), 0.27% to 0.18% (6MV-FFF), for field sizes from 4 x 40 cm2 to 40 x 30 cm2.

Discussions: The measurement of Sc with brass build-up cap was found to be slightly higher than PMMA mini phantom, suggesting the electron contamination at dmax depth. This emphasizes the need of Sc measurement at 10 cm with columnar mini phantom. Sc values of FFF photon beams were lesser than the FF photons beams. Our results confirm the removal of flattening filter causes a decrease in the head scatter factor. The effect of SSD is studied and has no influence on Sc . The presence of wedge influences the Sc value. The results also reveal that the Sc is higher, whenever X- jaw (which is actually MLC leaf bank) is set for higher field size. This may be due to the back scatter from the dose monitor chambers. The measured Sc values are in good agreement with the published data.

   P-116: Calibration of Ionization Chambers and Intercomparison of Radiotherapy Dosimetry in Bangladesh Top

Shakilur Rahman, Shamsuzzaman, Tanjim Siddiqua, Debasish Paul, Meher Nigar Sharmin1, Imrose Jahan2, M. A. Mamun2, S. M. Enamul Kabir3

Secondary Standard Dosimetry Laboratory, Health Physics and Radioactive Waste Management Unit, Atomic Energy Research Establishment, Savar, 2Department of Physics, Jahangirnagar University, Dhaka, 1Cancer Center, Khwaja Yunus Ali Medical College and Hospital, Enayetpur, Sirajgonj, 3Department of Radiotherapy. North East Medical College and Hospital, Sylhet, Bangladesh. E-mail: [email protected]

Introduction: Radiotherapy is the leading mechanism for the treatment of cancer patients in all over the world. External beam radiotherapy includes mainly high energy photon and electron beam from linear accelerator, tele-cobalt therapy. The outcome of the radiotherapy is highly dependent on how precisely the dose is delivered to the tumor which should not exceed ±5% of the prescribed dose including all types of uncertainties involved in the treatment procedure such as dosimetry, treatment planning and dose stability of the treatment unit etc. Current international protocols TRS-398 (IAEA), TG-51 (AAPM), and DIN-6800-2 (German) for absorbed dose to water determination are based on the calibration factor of the ionization chamber in-terms of absorbed dose to water with 60Co quality. To maintain the precisional dosimetry of radiotherapy beam the Secondary Standard Dosimetry Laboratory (SSDL) of BAEC acts as a link between the field oncology centers in Bangladesh and International Atomic Energy Agency (IAEA). The ionization chambers are used at the oncology centers in Bangladesh which are calibrated from SSDL, Bangladesh against reference standard. On the other hand, the best available process of quality assurance of dosimetry of field oncology centers are to participate intercomparison by postal dose quality audit. The details of calibration of ionization chamber and intercomparison program for radiotherapy dosimetry are discussed.

Objectives: The main objectives of this research program is to ensure dose delivering to the patients and traceability of radiotherapy dosimetry and QA performed by the radiotherapy centers in Bangladesh.

Materials and Methods: A total number of 23 thimble (0.1 cc to 0.6 cc) and 3 parallel plate ionization chambers of different oncology centers of Bangladesh have been calibrated in terms of absorbed dose to water at 60Co quality with standard procedure set-forth by SSDL. These chambers are regularly used for the dosimetry and Quality Control (QC) check of the respective radiotherapy centers. A participation of IAEA/WHO TLD intercomparison program has been initiated for cobalt and linac beams for oncology centers in Bangladesh by Thermoluminescence Dosimeter (TLD) postal dose quality audit program. A total number of 35 linac photon (4, 6, 10, 15 MV) and 5 cobalt beams of radiotherapy centers were participated in the intercomparison program under QA program. The TLDs (LiF powder) were irradiated with a dose of 2 Gy at reference depth 10 cm and field size 10 cm × 10 cm using standard water phantom. The irradiated TLDs were measured with PCL3 automatic reader (Fimel, France). Several correction factors such as holder, non-linearity and fading correction were applied for the absorbed dose to water measurement.

Results and Discussion: The maximum variation of calibration factors of the chambers between the manufacturer values and SSDL values have been observed within ±2.2% with an uncertainty of ±1.98% (k=2) for the determination of calibration coefficients at approximately 95% confidence level. The deviation of stated dose to measured dose of photon beams lies between 0.1-4.5% for linac photon and 0.6-4.0% for cobalt with an uncertainty of ±1.8% (k=1 ) . The discrepancies of one 15 MV photon beam was found 7.6%, that might be due the calibration factor of the ionization chamber. Three other photon beams were found in a large deviation which were detected due to dose calculation method. The reason of discrepancies was determined and correction is made by onsite visit by SSDL personnel.

Conclusion: The result shows an excellent agreement of calibration coefficient of ionization chamber provided by SSDL with previous values given by manufacturers. The Quality Assurance of dosimetry by hospitals meet good in agreement with international standard.

   P-117: Quality Assurance Tests of KV and MV Imaging Conducted on Novalis TX Linear Accelerator Top

V. Poopathi, Purnendu Adak, P. Nagendran, Saibal Mukherjee

Department of Radiation Oncology, Apollo Gleneagles Hospital Ltd., Kolkata, West Bengal, India. E-mail: [email protected]

Introduction: Commercial CT based Image Guided Radiotherapy systems allow widespread management of geometric variation in patient setup and internal organ motion. The physicist emphasis on reducing the volume of radiation therapy fields while maintaining or improving the precision radiotherapy. Reducing radiation related normal tissue toxicity, treatment position verification and correction before delivering radiotherapy had gained major importance. The LINAC manufacturers and third party vendors have developed integrated imaging systems to improve and facilitate internal patient anatomy visualization, enabling efficient positioning of the anatomical structures relative to the treatment room parameters.

Objectives: This work is to ensure the proper functioning of the integrated imaging systems in LINAC. To measure the dose contributed by the integrated imaging system and thereby ensuring the patient safety by kV and MV imaging procedures. It is also necessary to obtain proper quality of the images for the IGRT applications. Performance tests also ensure that the incorporated imaging systems will have the normal functions.

Materials and Methods: The use of imaging devices for verification and correction of patient position and target localization prior to treatment has spread widely. Novalis Tx linear accelerator include following three imaging system. i) Varian OBI system: OBI consists of two mounted arms – one for kV X-ray source (kVS) (generates photon spectra with kVp max to 150 kV/ 320 mA, collimates X-ray beam 2 X 2 cm2 to 50 X 50 cm2 at 100 cm from the focal spot) and other is flat panel Si detector (kVD) with size 40 X 30 cm2. ii) Electronic Portal Imaging Devices: EPID consists of flat panel detector with sensitive area 40 X 30 cm2 (features a matrix of 1024 X 768 pixel). EPID can be used for 2D radiographic acquisition or cine image acquisition. iii) Brainlab ExacTrac: Which includes dual diagnostic kV inclined (450) X-ray tubes and a-Si flat panel detectors with a robotic couch, infrared video detectors and set of infra-red markers. The detectors have pixel size 0.4 mm and maximum sensitive area is 20.5 X 20.5 cm2 with fatures a matrix 512 X 512 Pixel. The positioning accuracy of ExacTrac (±1 mm translational displacement and ± 1° rotational errors) can be a valuable tool in implementing frameless extra-cranial stereotactic radiotherapy.

Result and Discussion: The functionality of OBI and ExacTrac imaging system depends on various parameters such as kV and mA mechanical integrity tests and stability of X-ray tubes. We also evaluated the EPID for the safety and performance. The Winston-Lutz test was carried out for the isocenter verification. The isocenter measured was ≤1 mm. The measurement of LINAC isocenter and ExacTrac imaging isocenter was found to be within 1.1 ± 0.30 mm. The isocenter test for both kV and MV imaging was within 1.2 mm accuracy. The total filtration are measured as 3.15 mm Al for ExacTrac and for OBI 2.69 mm Al. The consistency of radiation output (CoV) are 0.005 for Exactracc and for OBI is 0.002. Accuracy of operation potential for both OBI and ExacTrac are with in ±1kV i.e. also within the tolerance limit ±5 kV. For kV imager mA linearity in terms of coefficient of linearity are within 0.02. In image quality test, visible hole is 2 mm for kv and for MV 5 mm and can resolve 1.5l p/mm. On position leakage at collimator level is 0.011 mGy in one hour for ExacTrac and that for OBI is 0.004 mGy in one hour.

We have reviewed the measured parameters and found, well within the tolerance limit. Our results also assure that the performance of the inbuilt imaging devices are suitable for radiotherapy applications.

   P-118: Evaluation Of Dosimetric Characteristics of 2D Ion Chamber Array Octavius 729 for CFF and FFF Beams Top

Bhagat Chand, Amrinder Singh Chhabra

Department of Radiotherapy, MM Institute of Medical Sciences and Research, Mullana, Ambala, Haryana, India. E-mail: [email protected]

Introduction: With advances in the radiotherapy techniques like IMRT and VMAT, more robust, fast, accurate and reliable device is required for pre treatment dose verification. There are several commercially available devices for this purpose. In order to attain sufficient confidence in treatment accuracy, it is customary for medical physicists, to perform all essential dosimetric checks of such devices before clinical use.

Objectives: This study was aimed to evaluate the dosimetric response and directional dependence of the two dimensional ionisation chamber array Octavius 729 in cFF and FFF beams and to validate the performance of this device for clinical use.

Materials and Methods: The detector Octavius 729 ion chamber array (PTW Dosimetry Germany) was used in this work. It has 729 vented ionization chambers, each of 0.125 cm3 volume, uniformly arranged over 27 x 27 cm2 area. The array was used with solid water phantom slabs and an octagon shaped phantom (Octavius Phantom). All measurements were performed on VersaHD medical linear accelerator (Elekta Medical Systems UK). PTW Pin-point ion chamber (0.015 cc), semiflex chamber (0.125 cc) and farmer chamber (0.6 cc) were used for comprehensive differentiation of parameters.

The device was analyzed for dose linearity, SSD, dose rate dependence and output factor for all available photon beam energies. The directional dependence as a function of beam angle was measured for 6MV and 6MV FFF beam energies. The methodology for direction dependent correction factors suggested by Boggula et. al. excludes the effects of mechanical factors and that of octavius phantom was used, according to which

where RMATangle and RICangle are the dose measured at angles other than zero degree, and RMATzero and RICzero are the dose measured at zero degree with array (MAT) and semiflex chamber (IC).

Results and Discussion: All the parameters measured in chamber array were compared with the ionisation chamber response.

Linearity: The coefficient of linearity (CoL) for dose higher than 20cGy was within tolerance value of 1% for all energies. For low dose range of 2cGy-10cGy the CoL was more than 1% for all energies and maximum value of 3.86% was found for 10MV FFF. The maximum variation in linearity was 1.889% for 6MV FFF.

Dose Rate Dependence: Dose rate dependence was evaluated energy wise from 50 MU/min to 2400 MU/min. The array was found almost dose rate independent. The maximum variation in response was found within 0.1% over the range of dose rates.

SSD Dependence: The detector array shows SSD dependence similar to the farmer chamber over SSD ranges from 85 cm to 115 cm. The highest deviation in response was at lowest and highest SSDs. The variation is + 1.0%.

Output Factors: The output factors were measured for 3 x 3 cm2 to 25 x 25 cm2 fields. The variation found in small fields was due to overestimation in response of matrix array. The deviation in output factor measurement was higher for FFF beams.

Directional Response: Directional response as function of beam angle in increments of 5 degree was measured for 6MV CFF and 6 MV FFF beams. The array shows directional dependence and, and maximum in the angles ranges from 88 degree-110 degree and 250 degree-272 degree. Maximum value of CF is 1.043 and 1.050 for 6MV and 6MV FFF respectively.

Many investigations have been done using this device in cFF beams but not much data is available for FFF beams. Necessary action levels should be established and proper calibration must be performed with profound accuracy before use in clinical practices and in plans involving small dosimetric fields.

   P-119: Performance Evaluation of Online Imaging Systems Attached to Medical Linear Accelerator Top

C. A. Shahan Shad, Dince Francis, Daicy George, V. Ramya, P. Suresh Babu, S. Sowmya Narayanan

Vydehi Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, India. E-mail: [email protected]

Objectives: During fractionated radiotherapy, it is essential to account for inter and intra fraction movements. Quantification of such variations are done using sophisticated linacs equipped with online imaging during Radiotherapy. This technology necessitates a comprehensive Quality Assurance (QA) program to maintain and monitor the system performance characteristics, which was established at the time of commissioning. The objective of this study is to perform periodic QA on imaging systems as per various protocols and to verify the functionality, accuracy, stability and image quality of the radiographic and CBCT mode.

Materials and Methods: We tested the real time imaging systems attached to two linear accelerators, viz Varian On-Board Imaging system (OBI) and Elekta XVI. The QA tests were divided into four parts: safety and functionality, geometric accuracy, image quality and generator checks.

Geometry QA verifies the geometric accuracy and stability of the system hardware/software such as imager isocenter accuracy, 2D-2D/3D-3D matches, couch shift accuracy, magnification accuracy, field size accuracy, scaling accuracy and central beam alignment. Image quality QA checks spatial resolution and contrast sensitivity of the radiographic and CBCT images. In addition to that HU linearity and uniformity, spatial linearity, and scans slice geometry were evaluated for CBCT images. Generator check ensured that the technical parameters (KVp and mA) applied onto the system were reproduced on the X-ray tube.

A cube phantom was used to study the agreement with treatment isocenter for both kV-images and CBCT images. A marker seed phantom was used to evaluate the applications in 2D/2D and 3D/3D image registration. Printed circuit board (PCB) was used for all other geometric QA. Leeds phantom was used for verification of image quality accuracy for 2D image sets whereas Catphan® phantom was used for CBCT images. A KVp meter was used to verify the generator performance and estimating dose for a given tube rating.

Results and Discussion: The isocentric accuracy of both imaging systems was found to be stable and within 0.5 mm relative to treatment isocenter over a period of one year.

The consistency in 2D-2D and 3D-3D match was found to be within tolerance. A maximum of disagreement from expected shift is observed as 0.5 mm and 0.4 mm for OBI and XVI respectively. All other geometric verifications were found to be within tolerances and consistent over the study period.

The radiographic image of Leeds phantom showed good spatial resolution (visibility of 11th and 15th line group for OBI and XVI respectively) and contrast resolution (18th disc for both system) for 2D images. CBCT images were verified with Catphan phantom and it shows appreciable spatial resolution (7-8 disc for both system) and contrast resolution (OBI-10th line group, XVI-14th line group). The HU measurements show that the CBCT imaging system is relatively stable over time. HU uniformity were found to be 0.6% and 0.15% for OBI and XVI respectively.

Conclusion: The online imaging system is one of the most attractive features of modern radiotherapy. The proper implementation of the unit results in acquisition of better desired clinical outcome. This study shows that the OBI and XVI are precise and stable in their performance. Geometric precision of the same are within 2 mm and it is maintained through periodic verifications. Precise performance of such online imaging system reduces the setup uncertainties and thereby enhances the confidence level in delivering highly conformal radiation therapy such as SBRT, SRT, SRS, IMRT and VMAT.

   P-120: Merit of 4D Octavius as a Pretreatment Quality Assurance Tool in Large Volume Target Irradiation Top

M. R. Mariyappan, S. Saraswathi Chitra, A. Donna, M. MuthuKumaran, V. Murali, Bhargavi Sanjay Chanderasker, B. Rajendran

Department of Radiation Oncology, Apollo Specialty Cancer Hospital, Chennai, Tamil Nadu, India. E-mail: [email protected]

Introduction and Objective: Volumetric Modulated Arc Therapy (VMAT) delivery technique has proven its capability in sparing critical and normal tissues when administering large volume target plans. In general practice of VMAT treatment technique, patient plan specific Quality Assurance (QA) has been done using stationary 2D detectors with or without phantoms. Availability of limited QA equipment and the equipment's own limitations demand the end user to ensure and verify the accuracy in delivering the complex highly conformal VMAT plans.

Materials and Methods: Patients with larger target volumes like Wilm's Tumor, whole Lung and whole abdominal RT, Mesothelioma tumors with concave shaped target, Lung Sarcomas etc., with volumes ranging from 1000 cc to 2250 cc are taken for the study. Treatment plans are generated in Varian Eclipse v13 using AAA dose calculation algorithm, with a single isocentric multiple arc VMAT technique.

Achieving coverage for large target volumes with optimal normal tissue sparing required multiple arcs, making the plans more complex and warranted for verification on multiple planes. The 4D Octavius with 729 detector array, a real 3D measurement tool combined with the dose reconstruction method presented a better option for multiple planar analysis with its special function called 4D volume analysis. The 4D Octavius phantom with inclinometer rotates synchronously with gantry acquires time and gantry angle – resolved dose measurements.

Verification plans are created on the 4D Octavius phantom and delivered using TrueBeam SVC Linear Accelerator (LINAC). Gamma Analysis with 4D was performed in PTW Veri Soft IMRT QA software, keeping Treatment Planning System (TPS) dose as reference dose against the acquired dose.

Results: For the ten plans taken up for this study, pass percentage ranged from 96.4%-100% points using analysis criteria of 3%-3 mm for 3D Gamma Evaluation. When 4D calculation methods is used multiple plane such as Axial, Coronal and Sagittal comparison is possible in Array Measured data against TPS dose matrix and the gamma pass percentage ranging from 96.6-99.1%. The evaluation of sample cases is shown in [Figure 1],[Figure 2],[Figure 3],[Figure 4].
Figure 1: Patient plan and Verification plan for Wilms tumor whole abdomen RT shows the organ sparing for the large volume target

Click here to view
Figure 2: Octavius measurement is evaluated and shows the gamma passing results are seen in OAR (Kidney and Liver) level. Second image depicts the volume analysis using 4 Dimensional calculation method

Click here to view
Figure 3: Patient plan and Verification plan for Mesothelioma tumors explains the complex shape of the tumor with organ sparing

Click here to view
Figure 4: Octavius measurement is evaluated and shows the gamma passing results are seen in OAR (Lung) level. Second image depicts the volume analysis using 4 Dimensional calculation method

Click here to view

Discussion: Patient oriented pre treatment checks in addition to the 2D planar verification with 4D Octavius demonstrated the actual level of dosimetric reliability in other planes, has given confidence in executing complex irradiation methods employing VMAT for large target volumes.

   P-121: Validation of the Octavius 4D System With Portal Dosimetry for VMAT Patient-Specific QA Top

L. Jose Solomon Raj, S. Timothy Peace, Henry Finlay Godson, I. Rabi Raja Singh, B. Paul Ravindran

Department of Radiotherapy, Christian Medical College, Vellore, Tamil Nadu, India. E-mail: [email protected]

Aim: To validate the Octavius 4D system with Portal Dosimetry using EPID for VMAT patient-specific QA.

Objectives: (1) To perform Patient specific QA using Octavius 4D and EPID. (2) To analyse the difference in gamma pass rate between EPID and Octavius 4D system.

Materials and Methods: The Octavius-4D system and EPID-based Portal Dosimetry were used to verify dose-maps for VMAT plans of 20 patients. Each plan consisted of two rotational arcs with a maximum dose rate setting of 600 MU/min. The recently acquired Octavius-1500 array detector consists of 1405 vented ionization chambers (0.44 x 0.44 x 0.3 cm3). The Octavius-4D detector measured dose-maps in synchrony with gantry rotation with detector orientation perpendicular to the central axis of the beam. The aS1000 EPID detector panel with active matrix of 1024 x 768 and detector resolution 0.39 mm was used to acquire the dose-maps at SDD of 105 cm and synchronous rotation with gantry. The Octavius-measured dose-maps were compared with calculated dose-maps using Verisoft Software while the EPID dose-maps were compared using Portal Dosimetry software by gamma evaluation method.

Results and Discussion: On evaluation of the VMAT plans using EPID and Octavius 4D, the global gamma evaluation (3 mm distance-to-agreement/3% dose-difference) was found to agree well with an average pass rate of 97.83% and 99.87% pixels respectively. The slightly lower pass-rate of the high-resolution EPID could be due higher detection probability of detecting errors to and the inability of the portal prediction to model MLC leakage. The Octavius 4D showed higher gamma pass rate while providing additional 3D reconstructed dose for the treatment volume.

Conclusion: Thus Octavius 4D system was validated with EPID and was found to provide accurate dose-maps when compared with the predicted dose maps. It is concluded that the Octavius 4D with its advantage of evaluating the 3D dose information empowers the authentication of delivered dose to the entire treatment volume and proves to be an ideal tool for VMAT patient-specific QA.

   P-122: Study of Radiological Characteristic of Solid Phantom Top

P. Kaliyappan, Vidya Shree

Govt. Stanley Medical College, Department of Medical Physics, Anna University, Chennai, Tamil Nadu, India. E-mail: [email protected]

Introduction: The several solid water phantoms have been developed as being enough to natural water that they can be used for radiation dosimetry purpose. We evaluate the water equivalency of water equivalent solid phantom materials in terms of the depth dose measurement. Acrylic solid water equivalent phantoms are used extensively for the dosimetry of photon and electron beam. There are situations where a solid slab phantom is required. Many radiation detectors are not waterproof in which case a solid slab phantom must be used. Solid slab phantoms are also more useful for routine measurements since they tend to be more robust and easier, convenient to setup for any radiation measurement than water phantoms.

Objective: To evaluate the radiological characteristic of Acrylic solid phantom for radiation dosimetry and to compare the measured percentage depth dose data with published depth dose date of BJR – report number-25.

Materials and Methods: Acrylic phantom material is a clear plastic with the chemical formula (C5H8O2)n, polymethylmethacrylate (PMMA). It is a water equivalent with polystyrene, material composition of polystyrene with an admixture of Tio2 (2.1% ± 0.2%). It has a mass density of 1.045 g/cm3, (Z/A)r value: 0.536, Electron density (e/g): 3.386 x1023, Electron concentration (e/cm3): 3.539 x1023. The acrylic study phantom consists of 25 numbers slab; among these there are 3 slabs with 2 cm thickness, 1 slab with provision of chamber insert and the other 21 slabs with thickness of 1 cm and 1 slab with thickness of 0.5 cm. The outer dimension of all the slab is 40×40 cm. To create adequate backscatter 5 cm of slab thickness placed below the ionization chamber which is used to measure depth dose beam data.

The measurements of Percentage Depth Dose of Acrylic solid phantom was carried out using Theratron Phoenix Cobalt-60 unit, 0.65cc ionization chamber along with CD-SSD-92 electrometer. PDD was measured at the treating distance of 80 cm SSD for various field sizes 6×6 cm2, 8×8 cm2, 10×10 cm2, 15×15 cm2, 20×20 cm2, 25×25 cm2, 30×30 cm2 and at depths ranging from 0.5 cm to 17 cm.

Result and Discussion: The PDD was calculated using measured depth dose data for various field size and depths. The measured PDD was compared with BJR-25 for all field size which indicates that the transmission through slab phantom are as similar to that of water, the range of deviation was found to be 0 to -0.01%, which reveals that the characteristic of slab phantom is in close agreement with water phantom. The accuracy of the slab thickness was checked and rescaled. According to the IAEA International Code of Practice TRS-398, solid phantoms in slab form such as polystyrene, PMMA, and certain epoxy resin “solid water” (water substitute) phantom materials such as solid water, can be used as solid phantom for dosimetry purpose.

Conclusion: The result of PDD conforms that the characteristics of acrylic phantom is similar to that of water. Therefore conclude that the radiation beam characteristics of the acrylic solid slab phantom are equivalent to water phantoms. This acrylic solid phantom can be used for clinical dosimetry and quality assurance purpose.

   P-123: Dosimetric Comparison Between the IMRT Plans with Three Different Beam Number Techniques in Patients with Carcinoma of Supraglottic Larynx and Investigate the Impact of Increasing Beam Numbers on PTVS as WELL as OARS Top

Shayori Bhattacharjee, Pranjal Goswami, Moirangthem Nara Singh, Shashi B. Sharma, Sachindra Goswami, Mithu Borthakur

Department of Medical Physics, Dr. B Borooah Cancer Institute, Guwahati, Assam, India. E-mail: [email protected]

Introduction: Radiation efficiency and treatment-plan quality are closely tied to beam angle arrangements and the number of beams used in IMRT. Based on which a retrospective study has been carried out to account the effects of increasing beam numbers.

Objective: The main objective of the study is to compare dosimetrically between the IMRT plans with three different beam number techniques in patients with Carcinoma of Supraglottic Larynx and investigate impact of increasing beam numbers on PTVs as well as OARs.

Materials and Methods: For our study, we included 10 patients which were planned on CMS XiO (4.80) TPS for seven-beam, nine-beam and eleven-beam techniques by step and shoot IMRT. All patients were simulated with contrast-enhanced CT imaging for better visualization of nodes and contouring were done in 3 mm slice thickness. The dose prescription for primary tumor (PTV1) is 66 Gy and for the nodal irradiation (PTV2) is 60 Gy, delivered in 30 fractions with the Simultaneous integrated Boost technique. Analyses were performed on comparing the Dose volume histograms (DVHs) values. Target coverage and plan quality were evaluated for parameters V95% and V107% of PTV, Dmax, CI and HI. In term of Dmax, the OARs being evaluated in this study were the Eyes, Optic Nerves, Optic Chiasm, Brainstem, Spinal Cord and in case of parotids and parotids-PTV both Dmax and Dmean values were analyzed. To determine statistical significant result, both Wilcoxon Signed-Rank sum test and Dunnet Multiplication Comparison test were performed for all the parameters.

Results: IMRT plan with Eleven-beam technique has shown better result w.r.t the parameters V95% and CI with p value 0.0084 and 0.0248 respectively for PTV2 and data presented in [Table 1]. In case of OARs, the DVHs analysis for both Left Optic Nerve and Spinal Cord shown that Eleven-beam was considerably best in reducing the Dmax dose with p= 0.0028 and P= 0.001 respectively as shown in [Table 2]. But in contrary to above two parameters, Nine-beam technique for Right Parotid and Seven-beam technique for Left Parotid with p= 0.0454and p= 0.0162 respectively shown better Dmax dose reduction compared to rest of the techniques. In addition to this, when the dosimetric data for OARs were analyzed by using Wilcoxon Signed Rank Test, statistically significant results were found in Left Optic Nerve, spinal cord, Right Parotid-PTV and Right Parotid. Eleven-beam technique was considerably found better in reducing the Dmax dose with (p= 0.0128 & p= 0.0065) for Left Optic Nerve and (p=0.0407& p=0.0137) for Spinal Cord when compared first with Seven-beam technique and then with Nine-beam technique respectively. But in case of both Right Parotid-PTV and Right Parotid, Seven-beam technique had shown better reduction in Dmean dose with p=0.0488 compared to Nine-beam technique.
Table 1: Statistical data for comparison of dosimetric parameters of both planning target volumes

Click here to view
Table 2: Statistical data for comparison of dosimetric parameters of all the organ-at-risks

Click here to view

Discussion: IMRT plan with Eleven-beam technique, achieved better PTV coverage with parameter V95% and CI compared to other two techniques. However Seven-beam technique has shown better in reducing the dose for OARs such as Right Eye, Right Optic Nerve, R Parotid-PTV, L Parotid-PTV, Left Parotid. But if we exclude the OAR Parotid then Eleven-beam technique has found better in sparing the OARs like Left Optic Nerve, Optic Chiasm, Brainstem, Spinal Cord. This is because a larger number of beams provide more parameters to adjust and therefore a greater flexibility to achieve the desire dose coverage to target and spare the OARs before comes.

   P-124: Feasibility of Computed Radiography for Performing Quality Assurance Tests of Teletherapy Machines Top

K. C. Mahitha, Jayapalan Krishnan1, Iqbal Ahmed

Department of Radiation Oncology, Victoria Hospital, Bangalore Medical College, Bengaluru, 1Department of Radiation Oncology, Mangalore Institute of Oncology, Mangalore, Karnataka, India. E-mail: [email protected]

Introduction: Some of the routine quality assurance procedures performed in Radiotherapy requires usage of films or Electronic portal imaging devices (EPID). Extended Dose Rate (EDR2) and X-omatV films are widely used and require processing post exposure which requires an automatic film processor or dark room facilities, which are almost non-existent in most institutes as they have migrated to digital radiography. Gafchromic films on the other hand are self-developing but are more expensive. EPID is a good alternative to films but is a facility only available with advance linear accelerators. Many institutions in India still function with telecobalt units and/or linear accelerator with basic facilities. Though films are a gold standard in radiotherapy, there is a need to find an alternative that is simple and cost effective to perform some of the frequency based quality assurance tests like Light and radiation field congruence, Spokes test for collimator, couch and gantry isocentre and Parallelism of jaws as per the TG-142 and AERB protocols.

Objectives: This study aims at finding the feasibility to use Computed radiography (CR) for performing quality assurance tests like Light and Radiation field congruence, Collimator, couch and Gantry spokes test and Parallelism of jaws in Telecobalt and Linear accelerator units.

Materials and Methods: CR cassette was used for the tests on Linear accelerator and Telecobalt units. For all the above mentioned tests except the gantry isocentre, the CR cassette was placed perpendicular to the beam axis with the gantry in 0o position. The cassette was placed and the sensitive plane of the cassette was matched at the isocentre with 1 to 2 cm build up in Telecobalt unit and no build up in Linear accelerator unit. Field size of 10x10, 15x15 and 20x20 cm2 were irradiated to check for the light and radiation field congruence with the minimum MU/ beam ON time. Lead wires were placed at the field edges and at the centre of field to distinguish the field edges. For the Collimator and couch isocentre the X jaws were closed completely and the Y jaws were opened to 20x20 and the Collimator and couch were rotated at a 30 degree interval to obtain a star pattern. The gantry isocentre test was performed in a similar fashion but with the CR cassette placed vertically on the couch. These tests were only performed on the linear accelerator unit and not on the Telecobalt unit because of the machine limitations. To check for the parallelism of jaws the CR cassette was irradiated for a field of 10x10 anteriorly and a field of 20x20 posteriorly. Lead wires were placed at the field edges for ease of measurement. The garden fence test for quality assurance of multileaf collimators (MLC) was also performed to check whether CR can be an additional tool for the MLC static and dynamic positional quality assurance procedures.

Results and Discussions: The results were within the tolerance limits for the respective tests. CR cassettes provided images with good contrast and resolution with minimum exposures and are a good alternative to films as they mimic the film in most aspects (except dose rate) but are reusable, inexpensive and much easier to process unlike films. These can be a good alternative in place of films at institutes with no facilities for electronic portal imaging and/or where they cannot afford to use slow films for routine quality assurance procedures.

   P-125: To Investigate the Effectivenss of Edge Detector for Depth Dose Measurement in Buildup Region of 6 and 10 MV FFF Photon Beams Top

A. S. Jagtap1,2, C. V. Arundev2

1Department of Physics, Savitribai Phule Pune University, Pune, 2Department of Radiotherapy, Alexis Multispeciality Hospital, Nagpur, Maharashtra, India. E-mail: [email protected]

Objectives: To investigate the effectiveness of the edge detector over 0.125 cc cylindrical chamber and parallel plate chamber for the measurement of percentage depth dose curves in the buildup region of 6 and 10 MV FFF beam for the commissioning.

Introduction: Commissioning is one of the most important parts of the entire QA programme for both the treatment planning systems (TPS) and the planning process. Dosimetric parameters such as percentage depth dose, profiles and output factors are important for the commissioning of treatment planning systems in radiotherapy. Nowadays, along with nominal photon beams, flattening filter free (FFF) beams are being used for the treatments where high dose is required in single or few fractions. Since FFF beam uses very high dose in very short time, the accurate measurement of dosimetric data for FFF beam becomes very important. Thimble ionization chamber with volumes of the order of 0.1-0.2 cc is commonly used for these types of measurements. The disadvantage of 0.1-0.2 cc chamber is they are not suitable for the measurement of PDD in shallow depths due to the wrong estimation of surface doses. A buildup region is the most sensitive region of PDD curve, which if not measured accurately, would lead to wrong dose calculations by TPS.

Materials and Methods: For this work, all the measurements are done on Varian made TrueBeam machine. This machine is equipped with 6, 10, 15 MV nominal photon beams and 6, 10 MV FFF beams. We have used 6 & 10 MV FFF beam for PDD measurements, especially in the buildup region. PDD is measured for 5x5, 10x10, 15x15, 20x20 cm2 field sizes at source to surface distance of 100 cm. Three chambers, including 0.125cc cylindrical chamber, edge detector and parallel plate chamber from Sun Nuclear Corporation have been used for the PDD measurement in a circular water phantom. All the measurements and setup are done according to the TRS-398 protocol.

Results and Discussion: For all field sizes and both FFF photon beams, in buildup region, parallel plate chamber is giving more PDD values as compared to the edge detector and 0.125 cc ion chambers. The surface dose of 6MV FFF beam at a depth of 0.5 mm measured for 5x5 cm2 field size by edge detector, 0.125 cc ion chamber and parallel plate chamber are 60.15%, 61.90%, 74.21% and for 20x20 cm2 field size it is 67.28%, 69.21%, 79.08%. However, The surface dose of 10 MV FFF beam at a depth of 0.5 mm measured for 5x5 cm2 field size by edge detector, 0.125 cc ion chamber and parallel plate chamber are 43.55%, 44.44%, 55.51% respectively and 51.35%, 52.73%, 62.79% respectively are for 20x20 cm2 field size. The value of Dmax for 6MV FFF using edge detector, 0.125 cc ion chamber and parallel plate chamber are 1.26 cm, 1.27, 1.139 cm respectively for 5x5 field size and 1.27 cm, 1.14 cm, 1.145 for 20 x 20 cm2 field size respectively. Similarly the value of Dmax for 10 MV FFF beam using edge detector, 0.125 cc ion chamber and parallel plate chamber are 2.14 cm, 2.14 cm, 2.14 cm respectively for field size of 5x5 cm2 and 2.03 cm, 2.01 cm, 1.89 cm respectively for 20 x 20 cm2. It has been concluded that edge detector is good choice for the measurement of PDD in the buildup region during commissioning.

   P-126: Is the TPS Need to Recommissoned After the Replacing the Beam Center Alignment? Top

C. Krishnappan1,2, C. Anu Radha2, G. Madhan Kumar1, J. Antony Paull1

1Department of Radiation Oncology, Apollo CBCC Hospitals, Gandhinagar, Gujarat, 2School of Advanced Sciences, VIT University, Vellore, Tamil Nadu, India. E-mail: [email protected]

Introduction: In developing countries like ours wherein the ratio of the number of linacs available per million population is very less, the patients need to travel miles to get the radiotherapy treatment. Naturally, it is expected to maintain as minimal downtimes as possible and finish the treatment at earliest. But Instances like the failure of ion chamber, waveguide or beam centerline requires an enormous amount of post replacement work from a medical physicist so as to ensure radiation safety to patients. The quality assurance (QA) work starts with few basic tests and measurements to check for the beam properties. The big challenge for the physics team is to take the call on beam data matching, the entire beam data have to compare and match with the previous data on which the TPS is being commissioned.

Objectives: Assurance of the beam matching after replacing the beam center alignment of the Varian Unique machine.

Materials and Methods: To check the feasibility to continue the same existing beam data of 6MV Xray in TPS, different types of plans which were earlier generated with old beam data in TPS were delivered at machine, measured in a phantom and the results are compared. Point dose measurements have made for three open fields, static MLC fields at different region as mentioned in TG 53 and its comparison with TPS calculated value. And For dynamic treatemnts TG 119 Test cases are compared at point dose with portal dosimetry levels. The generated plans for some test cases are shown in [Figure 1]. For patient specific assurance especially of the treatments like IMRT/Rapidarc, three patients each with different sites (Brain, H&N, Pelvis) which are planned earlier with old data. Patient specific QA of point doses at isocenter and off axis were measured and compared. Also IMRT/VMAT QA has been repeated and verified using EPID for the same patients. For evaluation the portal dosimetry the 3 mm/3% DTA/DD criteria is set.
Figure 1: Plans generated for the TG119 test case suite

Click here to view

Results and Discussion: For Maximum point dose vartiation at static (open & MLC) fields for the inner and outer region is 1.3% & 0.90% of the field size of 25x25 cm2. For the same static fields the maximum variation of buildup and penumbra region is 2.4% and -11.70% of the field size of 25x25 cm2 and 10x10 cm2 respectively. In the case of dynamic fields TG 119 Test case plan QA results the confiedence limit is 0.022 and 0.033 for high and low dose region. The portal dosimetry results for the same test cases the average area gamma variation less than one are 98.4%. Patient specific point dose QA results for all IMRT/Rapidarc plans were found less than 1.6%. Analysis of portal dosimetry for the same patients plans average area gamma variation less than one are 97.6%. Our results show that after the replacement of beam center alignment, there is no significant variation at machine specific or at patient specific QA due to beam data. The 6MV photons before and after beam center line replacement are said to be matched and clinically patients can be taken with greater confidence without any need for beam data modification in TPS. Since the beam center alignment is directly related to the beam data without a second thought, it is recommended to ensure the beam data matching before and after the replacement. If any notable difference is found at any stage it is better to recommissioned the beam data.

   P-127: Patient Specific IMRT QA by Using EBT Gafchromic Film QA PRO2016 Software – Initial Experiences Top

V. R. Gedam, P. S. Negi, M. Sasindran, M. Mahur, R. Sharma, A. Singh, D. Kumar, R. K. Grover

Delhi State Cancer Institute, Delhi, India. E-mail: [email protected]

Introduction: Radiographic films have been regularly used in routine commissioning of treatment modalities and verification of treatment planning system. The radiation dosimetry based on radiochromic film has ability to give absolute two-dimensional dose distribution and prefer for the IMRT quality assurance. It is mandatory to do patient specific dose verification before irradiating the plan on patient. To ensure accurate radiation delivery before IMRT treatments, pretreatment verification prior to clinical implementation must be adequately tested in the form of delivery quality assurance to identify any potential errors in the treatment planning process and in machine deliverability. Various two-dimensional (2D) array quality assurance systems have been used for patient specific IMRT QA.

Objective: The purpose of this work is planar dose measurements were performed using Film QA Pro2016 software and compare result with ImatriXX 2-D array system of IBA. Percentage of pixels passed the 3%-3 mm gamma criterion (% dose difference and distance to agreement-DTA) was taken for the comparison. Point dose measurements were also performed and the percentage deviation of the calculated doses versus measured doses was compared.

Materials and Methods: Gafchromic EBT3 films were irradiated at different dose levels between 50cGy to 400 cGy with open fields 10 x 10 cm2 at SSD setup and film at 5 cm depth on 6MV Oncor Expression linac. After 24 hours scanned all films on Epson Expression 11000-XL flatbed scanner and calibration curve drawn for each color blue, red, and green.

Patient specific QA was performed for 10 IMRT plans and analyzed measurements are presented here. We took 5 brain and 5 head and neck plans made on Monaco TPS 5.11.01 by using Monte Carlo algorithm. Made IMRT patient QA plans for each patient and irradiate on the solid phantom with film and on the imatrix on the linac and measured dose distribution. Now compared these dose distributions with TPS calculated dose distribution by using IMRT OmniPro software and Film QA pro2016 software. Calculate the gamma and DTA of the compared plan by using gamma index method. QA results are considered acceptable when the passing rate is greater than 95% using the gamma criteria a tolerance of dose difference (DD) of 3% and a tolerance for distance to agreement (DTA) of 3 mm

Result and Conclusion: The pretreatment verification of the IMRT for the two treatment sites was evaluated using two QA systems. The IMRT patient QA plans were verified using the gamma index method and found to be within acceptable criteria. Overall, this study confirmed that both the QA systems perform well in terms of delivery errors. However, excellent agreement (more than 90%) between the measured and calculated dose distributions for the both criteria was found for both the QA systems and treatment sites. Therefore, the results of this study suggest that the Film QA systems are also reliable verification systems for IMRT pretreatment as Imatrixx system.

   P-128: ANALYSIS of Photon Beam Skin Dose for Physical and Enhanced Dynamic Wedges for Different Field Sizes for 6 MV and 15 MV Photons Top

Baljeet Seniwal1,2, Ranjit Singh2, Arun S. Oinam2

1Centre for Medical Physics, Panjab University, 2Department of Radiotherapy & Oncology PGIMER, Chandigarh, India. E-mail: [email protected]

The introduction of high energy linear accelerator in radiotherapy allows treatment of deep seated tumors with better dose homogeneity and conformity. The greater penetration of high energy mega-voltage X-rays results in reduction of doses to the skin surface. Apart from primary radiation, electron scattered from collimator head and patient's body contributes significantly to the skin dose. The patient scattered depends upon area of the irradiation and the contribution from collimator depend upon it's distance from the patient's surface. The commercially available treatment planning algorithm (Pencil beam algorithm (PBC), anisotropic analytical algorithm (AAA)) shows a significant variation at the surface interface and the dose gradient region. Various beam modifying devices (e.g., wedges, shielding block, Multi leaf collimator (MLCs) etc.) are used in treatment planning system to adequately cover the target volume with the prescribed dose without exceeding the doses to the normal structures. The wedge filters are commonly used as a tissue compensator and it results in tilt of iso-dose curve toward thicker end. Physical and Enhanced dynamic wedges (EDW) are the two main class of wedge filters routinely used in radiotherapy. The skin dose drastically changes with the introduction of these two classes of wedge filters. The aim of the present study is to evaluate skin doses for 6 MeV and 15 MeV photon beams at different field sizes (5 × 5, 10 × 10, 15 × 15, 20 × 20, and 40 × 40 cm2) and for different wedge angle (15°, 30°, 45° and 60°). The experiment was performed on Clinac DHX dual energy linear Accelerator (Varian Oncology Systems, Palo Alto, CA). The solid water phantom RW3 (dimension 30×30 cm2, 0.1-1 cm thickness range) (density 1.09 g/cc), parallel-plate ion chamber (PPC-40(IBA(S/N-913) and supermax (Standard Imaging (S/N-P09133, +300 V polarizing potential) electrometer were used for the measurement. The source to surface distance (SSD) was 100 cm and all measurements were carried out upto a depth of 4 cm with backscattered thickness of 15 cm. The percentage depth dose data were measured for all wedge angles and field sizes. The meter readings (electrometer) were recorded and normalized with the meter reading obtained at the depth of maximum dose. The percentage depth dose at surface (PDD0) increases with the increase in field size, both for enhanced dynamic (EDW) and physical wedged (PW). The surface doses are slightly higher for EDW as that for same angled physical wedge.

   P-129: Dosimetric Evaluation of Flattening Filter Free and Flat Beams on Elekta Infinity Linear Accelerator Top

Vyankatesh Shejal, K. K. D. Ramesh1, N. Vinod Kumar, R. Ramu, Sebeerali

Department of Radiotherapy, Manipal Hospital, Bengaluru, 1Department of Radiotherapy, Manipal Superspecialty Hospital, Vijayawada, Andhra Pradesh, India. E-mail: [email protected]

Introduction: Elekta Infinity linear accelerator system with agility head introduces a number of novel components which could uniquely impact imaging and treatment workflows. Existing linear accelerator configuration has standard features such as dynamic leaf guide, no backup jaws and Standard dose rates. One hundred and sixty 5 mm (projected width at isocenter) multileaf collimators (MLCs) travel up to 3 cm/s over the full 40x40 cm2 field-of-view. The MLC carriage can travel at 3.5 cm/s for a maximum MLC leaf speed of 6.5 cm/s. However since higher dose rate on the existing machine was not a licensed option; this study was intended towards the licensing/type approval testing of High dose rate modes on Infinity linear accelerator.

Objective: The purpose of this study was to qualitatively evaluate the dosimetric characteristics of flattening-filter-free (FFF) and flattened beams on Elekta Infinity Medical Linear accelerators after its upgrade with High dose rate mode.

Materials and Methods: Two Elekta Infinity Medical Linear accelerators (Sr. No. 153324 & Sr. No. 153237) were qualitatively evaluated in this study. During the acceptance testing and commissioning measurement of unflat mode, prior upgrade & post upgrade measurements were performed on Elekta Infinity linac equipped with 160 leaf multi-leaf collimators (MLCs), five photon (4 MV, 6 MV, 10 MV, 6 FFF and 10 FFF) and six electron energies. The beam data's were confirmed to be within the manufacturers and National Task Group recommendations for its clinical use. Primarily, mechanical and dosimetric data's were measured and evaluated to check the consistency of data. The analyzed data included the PDDs, profiles, penumbra measurements, surface doses, out-of-field doses, output factors & MLC transmission for flat and unflat beams on Elekta Infinity Linear accelerator.

Results and Discussions: The Measured TPR20, 10 Values in both 6 and 10 MV flat & unflat modes were found identical. In comparison to flattened beams, Dmax for FFF beams was deeper for all field sizes measured. The 6MVFFF and 10MVFFF beams had higher surface doses than the corresponding flattened beams for field sizes of up to 10X10 cm2 but had lower surface doses for larger fields. The penumbras of FFF beams for smaller field sizes were found to be sharper than those of flattened beams due to the reduced head scatter however a wider penumbra was observed for larger field sizes. The FFF beams showed smaller variations in beam quality along the off-axis in comparison with flat beams. The head scatter factor on an average showed lesser variations for the 6MVFFF and 10MVFFF beams, respectively and the variations in the phantom scatter factor were also smaller. Both FFF beams had lower average MLC transmissions & the out-of-field doses than the flattened beams.

   P-130: Comparative Study Of Percentage Surface Dose Measurement for 6MV Flattened and 6MV Flattening Filter Free Photon Beams Using Parallel Plate Chamber Including and Excluding its Over-Response Correction. Top

Srimanta Pamanik, Dilip Kumar Ray 1, Arka Choudhury, Asik Iqbal, Amitabh Ray, Sayan Kundu, Sandip Sarkar

Department of Medical Physics, Chittaranjan National Cancer Institute, 1Department of Medical Physics, Ruby General Hospital Ltd., Kolkata, West Bengal, India. E-mail: [email protected]

Objectives: The purpose of this study was to investigate the surface dose of 6MV flattening filter free (FFF) photon beam in the build-up region and to compare it with 6MV flattened (FF) photon beam with the help of parallel plate chamber with and without its over-response correction. Correction factors are specific to each chamber as ion chamber has its own guard size, plate separation and volume.

Materials and Methods: A Varian Clinac iX with 6MV FFF mode linear accelerator has been in clinical operation with 6MV, 15MV, flattened and 6MV (FFF) unflattened photon beams. The entrance dose was measured for 6MV FF & 6MV FFF energies using a parallel plate chamber (Markus; product code-23343; PTW Freiburg) with a thin (0.025 mm) entrance window of water equivalent material in a solid water phantom with build-up region 0-20 mm depth for different field sizes 5x5, 7x7, 10x10, 15x15, 20x20, 25x25 and 30x30 cm2. In SAD technique we measured the tissue maximum ratio (TMR) with temperature and pressure correction and was converted into PDD with over response correction (Mellenberg correction) for parallel plate chamber. From the above measurement we had found a depth-dose curve which was a sixth order polynomial equation for each field size. From the polynomial equation percentage surface dose had been calculated at 0.5 mm depth.

Results and discussion: The percentage surface dose was measured from sixth order polynomial equation (Y = aX6 + bX5 + cX4 + dX3 + eX2 + fX + g), where Y and X were percentage dose and depth (in mm) respectively. The study shows the percentage surface dose was 5 to 7 percent higher for 6MV FFF photon beams than 6MV FF photon beams for all field sizes. The percentage linearly increased with field size for both energies. Applying over response correction for Markus type parallel plate chamber, the percentage surface dose reduced significantly up to 10 to 12 % for both energies from uncorrected over response values for all considered field sizes.

Conclusion: The estimation of surface dose in the build up region without over-response correction for parallel plate chamber shows over dose for both flattened and unflattened photon beam. For surface dose measurement in the build-up region one should consider the overresponse correction for the considered ionization chambers for all photon energies and field sizes.

   P-131: Measurement of Percentage Depth Dose Based on Point Dosimetry for Telecobalt Units Top

A. Hemalatha, M. Athiyaman, Arun Chougule1, Ganga, H. S. Kumar2

Departments of Radiological Physics and 2Radiotherapy, S.P. Medical College and AG Hospitals, Bikaner, 1Department of Radiological Physics, S.M.S Medical College, Jaipur, Rajasthan, India. E-mail: [email protected]

Introduction: Percentage depth dose is one of the essential parameters for dose calculation for teletherapy based treatment machines. The telecobalt units percentage depth dose of any cobalt machines are taken from the published data such as Br J Radiol 1978, and related appendix provided in various text books. The clinical physicist have to follow the published tables for dose calculation for SSD based treatments. Even though these tables provide accurate values of PDD there may be a need to verify these published values; In routine the PDD values can be measured only with the beam profiler and hence the hospitals that have single telecobalt units may lack of having the beam profiler. In this study we attempted to provide a solution to measure the PDD values based on point Dosimetry by clinically used secondary standard dosimeter. The measured PDD values by our suggested method was compared with the standard published tables and their percentage of deviation is estimated.

Objective: To estimate the PDD values of three telecobalt units available in our department based on point Dosimetry by using Farmer type Ion chamber.

Materials and Methods: The ionization measurements are carried out in the telecobalt units. Solid phantom with thickness of 1gm/cm2 is used for this study. Measurements were performed at the depths of 1 cm, 5 cm, 10 cm, 15 cm, 20 cm & 25 cm for the square field sizes 5, 10, 15, 20, 25, 30 cm2. Considering the necessity of getting the dmax ions at surface is measured by keeping SSD 79 cm and the ion chamber at 1 cm depth. The Dmax is estimated by interpolating the values of 1 cm & Surface measured values. All the other values are normalized with respect to the 0.5 cm values. The in-between values are estimated by applying Linear interpolation method. The obtained values were compared with the standard published tables and their percentage of deviation was estimated.

Results: To gain initial confidence on this work the standard and routinely used values, PDD @ 5 cm & 10 cm depth for 10x10 cm2 are noted in the calculated values. It is found that the calculated PDD values were 78.5% & 55.6% respectively for 5& 10 cm depths. The estimated average percentage of deviation is within -0.68% and maximum of 3.85%.

Discussion: The proposed method of measuring the PDD, interpolating from the fixed depth ionization values, can be used in telecobalt units for cross verifying the standard published values. This method is performed without the beam profiler. Also this can be extended to linear accelerator measurements.

   P-132: Comparing and Estimating the Buildup Dose for 6MV and 10MV Photon Beam with FF and FFF Using Various Detectors Top

S. Surekha, G. Bharanidharan, Prakasarao Aruna, J. Velmurugan, P. Thamilkumar1, R. R. Rai1, S. Singaravelu Ganesan1

Department of Medical Physics, Anna University, 1Department of Radiotherapy, Dr. Rai Memorial Cancer Institute, Chennai, Tamil Nadu, India. E-mail: [email protected]

Introduction: During the last years Radiotherapy has been practiced with flat beam profile. Recently, evolution of technology introduced a Flattening Filter Free photon beams which have stimulated medical physicist to carry out the research in radiotherapy. The removal of flattening filter alters the physics around flattening beam and the significant increase in dose rate causes softening of beam spectrum and reduction in scatter as well as decrease in neutron and photon leakage in the head.

Objective: The current study aims to compare the buildup region with FF and FFF beam for 6MV and 10 MV photon beam in a Varian True beam Medical Linear Accelerator.

Materials and Methods: The Linear Accelerator True Beam with longstand which was calibrated to deliver a dose of 1cGy per MU at 10 cm depth of water, a reference field size of 10 cm ×10 cm and a source to surface distance of 100 cm for 6MV and 10MV respectively. The detectors used were Ionization chamber, Diode detector, MOSFET (Thomson Neilson) and EDR3 Radiochromic film.

Results and Discussion: The buildup region was measured using Ionization chamber, Diode detector, MOSFET and Radiochromic film by placing the detectors at a distance of 98.5 cm and 97.5 cm at a SSD of 100 cm for 6 MV and 10 MV photon beams and 0.5 cm thickness slab were introduced one above the other to check the buildup dose for 6 MV and 10 MV photon beams. The dose response of the detectors shows that for both 6 MV and 10 MV photon beams with FFF the dose measured was higher than the FF which may be due to the scattered dose. Ionization chamber, Diode Detector and Radiochromic film shows a linear response whereas MOSFET shows linearity within slight deviation.

Conclusion: Determination of buildup dose were carried out using Ionization chamber, Diode Detector, MOSFET and Radiochromic film which clearly states that for both 6 MV and 10 MV photon beam with FFF shows a higher build up dose than beams with FF and no significant dose response was found between the detectors. Hence the study clearly concludes the buildup dose with FFF is higher than FF but the difference between the two is not significant.

   P-133: Fabrication of Quality Assurance Tools for Quick Quality Assurance Testing of Linear Accelerator Top

S. D. Mishra

HCG-MNR Curie Cancer Centre, Ongole, Andhra Pradesh, India. E-mail: [email protected]

Introduction: The quality assurance tests are essential to ensure the proper functioning of the medical linear accelerator within the requisite tolerance. Various tools are required to carry out these tests. Considerable time has to be spent to carry out these tests.

Objectives: Some quality assurance tools are fabricated in the Radiotherapy Department of our centre with the following objectives.

  1. Saving time by providing facility of carrying out many tests with one tool in one setting.
  2. Providing an affordable alternative to costly imported tools with comparable quality.

Materials and Methods: Following tools are fabricated in the department.

  1. One water phantom with a leveled platform is so fabricated that all required daily quality assurance tests can be carried out using this in one setting. This phantom can be utilised for quality index of the beam also.
  2. One versatile tool to check the congruency of light field with the radiation field visually. This tool helps avoiding the inherent subjectivity in such test.
  3. One accurate scanner mechanism which can be operated manually as well as electronically. This fits on the existing 30 cm X 30 cm X 30 cm water phantom. Beam profiles can be drawn on the graph paper with the help of this. Symmetry and flatness of the radiation beam can also be determined. This mechanism can be used to scan radiation beam in air. This can also be used to check the radiation field congruency with the light field.

Results and Discussion: These tools are easy to use. The setting time of these tools for the measurement is very less. These tools are cheap. The results of tests carried with these tools are comparable to the results obtained for the same tests with standard and expensive tools.

Conclusion: The quality assurance tools developed in the department are useful for a busy radiotherapy department. These tools are also affordable for the department with limited resources.

   P-134: Impact of Photon Beam Attenuation and Modeling of Treatment Couch: Angle and Energy Dependence Top

M. Rafiqul Islam1,2, P. Colleoni2, C. Bianchi2, M. Fortunato2, S. Andreoli2, M. Monjur Ahasan1

1Nuclear Medical Physics Institute, Bangladesh Atomic Energy Commission, Bangladesh, 2Department of Medical Physics, ASST Papa Giovanni XXIII Hospital, Bergamo, Italy. E-mail: [email protected]

Introduction: Nowadays Carbon fiber is the material of choice for radiotherapy treatment couch. Attenuation of the photon beams is influenced not only by the thickness of the carbon fiber used in the construction of the couch surface but also by the internal materials used to sandwich the plies. The dosimetric impact from couch on dose calculation is a complex combination of increased skin dose, reduced deep dose and modified dose distribution.

Objectives: The objective of this study is to quantify the attenuation of megavoltage photon beams through carbon couch at various angles and energy and to find the correct modelling of the treatment couch parameters in the treatment planning system (TPS). A method for the evaluation of the most appropriate Hounsfield Unit (HU) sets is proposed.

Materials and Methods: The transmission of 6 MV and 15 MV photon beams from linear accelerators (Varian, USA) through IGRT carbon fiber couch was measured using the 10X10 cm2 field size for various gantry angles. A cylindrical ionization chamber (semiflex 31010, PTW, Germany) with 0.125cc volume was inserted inside a 30x30 cm2 slab phantom (1.045 g/cm3) (RW3 Phantom PTW-Germany). The chamber was positioned at isocenter in the middle of a 10 cm high phantom. The attenuation was measured for two beam angles: oblique (45°-135°) and orthogonal (0°-180°), for three couch thickness (thin, middle and thick). In the TPS (Eclipse Varian – V10.0.34) the attenuation of the treatment couch model was evaluated for different sets of HU numbers. Measured and calculated attenuation was optimized to find the best modelling inside TPS.

Results: The most significant beam attenuation was observed with thick couch and oblique incidence, respectively 3.2% for 6 MV and 2.0% for 15 MV. The smallest attenuation was observed with 15 MV beam and thin couch (0.3%). Minimum aberration between the calculated and measured attenuation of the treatment couch was found for the HU values of -700 HU for the carbon couch surface, -960 HU for the inner part for 6MV and 15MV beams.

Discussion: The geometrical model of the couch in the TPS is reliable and no CT scan of the real couch seems to be necessary. A limited set of measurements for the three couch thicknesses provides reference values for attenuation at different gantry angles for low and high energy beams. This method of couch attenuation modelling into the treatment planning system is fast and easy and can result in more acceptable dose calculation accuracy.

   P-135: Estimation of Uncertainty Budget in Cross Calibration of Small Volume Ionization Chambers in CO60 Beam – an Approach Towards Quality Control in Dosimetry Top

Narender Kumar, LibinScaria, Rajesh Kinhikar, C. M. Tambe, J. P. Agarwal1, D. D. Deshpande

Departments of Medical Physics and 1Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: The advance radiotherapy (RT) involves high precision treatments like SRT, SRS, IMRT and VMAT which includes small fields. The dosimetry with the benchmark small volume detectors is extremely desired. Ionization Chambers (IC), supposed to be the benchmark detectors for such dosimetry need to be monitored for its valid calibration coefficient provided by Primary Standard Dosimetry Laboratory (PSDL) or Secondary Standard Dosimetry Laboratory (SSDL) traceable to PSDL. Due to ageing or post-major repairs and possible damage, response of the IC and in turn the calibration coefficient may change. Due to the limitations and logistics, PSDL may have challenges to calibrate small volume chambers for the entire country. At busy institutes, it may be challenging to keep the track of the calibration validity of the detectors and this may raise a question or there may be an ambiguity to use these detectors for absolute dosimetry for high precision RT to maintain high quality control in dosimetry. This can be overcome by cross calibrating chambers against a reference chamber traceable to PSDL. The cross calibration alone is not sufficient, hence one need to estimate the uncertainty budget as well. At our institute we have multiple ICs (with different volumes), out of which more than 10 chambers were found with calibration date expired.

Objective: To cross calibrate small volume ionization chambers & to estimate Uncertainty (Type A & B) Budget.

Materials and Methods: Chambers to be cross calibrated are three IBA CC13 (0.13cc), two PTW Semiflex (0.125cc), two Tomotherapy chambers, Standard Imaging A1SL (0.053cc), one IBA PPC_05, one PTW Pinpoint Chamber (0.015cc). An IAEA protocol TRS 469 was used for this purpose. All the measurements were performed at 5 cm depth in water with Elite 80 telecobalt machine for reference field size of 10 cm x 10 cm at source to axis (SAD) distance of 80 cm. Substitution method was followed, and a recently calibrated chamber FC65G, (0.6cc) was used as Reference chamber. Reference chamber's central electrode was placed at 5 cm depth and irradiated for 2 minutes, multiple reading were collected at +300, -300 & +150 volts to estimate saturation & polarity correction factor, temperature & pressure reading were noted for estimating KT,P correction factor. Shutter timer error was also taken into account. Reference IC was replaced with Field chamber to be cross calibrated and whole set of measurement was repeated. Ratio of mean value of corrected meter reading of two chambers and value of calibration coefficient of Reference IC were used to calculate calibration coefficient for field IC. For uncertainty budget estimation Guide to Uncertainty Measurement (GUM) & IAEA Tecdoc-1585 were followed. For Type A uncertainty: positional uncertainty, uncertainty in meter reading collected (reproducibility), and uncertainty in temperature were estimated. For Type B uncertainty due to Resolution of electrometer, Thermometer, Barometer& uncertainty quoted in calibration certificate provided from PSDL for reference chamber were estimated. Finally total relative standard uncertainty was estimated.

Results and Discussion: Calibration coefficient for each detector were calculated and percentage deviation from the original calibration certificate (old ND,W) were estimated. The mean deviation (percentage) for CC13 0.36% (0.27 to 0.63%), Semiflex 1.05% (0.33 to 1.78%), A1SL 1.58% (1.03 to 1.87%), PPC_05 0.34%, Pin_Point 3.68%. Uncertainty in ND,W @ 95% (or 2σ) confidence level is ±3%. It was observed that due to ageing Response of Pin point Chamber might changed, new calibration coefficient has been estimated and being used for small field dosimetry.

   136: Characteristics Comparison Between Physical Wedge And Virtual Wedge Using 6 MV Photon Beam Top

N. Singh, A. Sinha1, K. Purushothaman1, R. N. L. Srivastava1, N. K. Painuly, T. Verma, S. Srivastava

Department of Radiotherapy, King George's Medical University, Lucknow, 1Medical Physics Section, J.K. Cancer Institute, Ganesh Shankar Vidyarthi Memorial Medical College, Kanpur, Uttar Pradesh, India. E-mail: [email protected]

Introduction: In modern era most of the cancer centers are having Megavoltage Linear Accelerator machines. From the supplier of LIANC, wedge filters were supplied as accessories. Besides physical wedge, virtual wedge produces the same wedge intensity gradient by closing one jaw gradually while the beam is in on position. Wedge can be used to compensate for sloping surface as well to compensate for missing tissues. In our study we discuss about the charactertiricts of both types of wedge taking in to account various parameters. Further surface dose was also measured using both type of wedge.

Objective: This study aims to investigate the physical characteristics of the physical wedge and virtual wedge for clinical conditions.

Materials and Methods: Siemens Primus Linear Accelerator has been used for the study having dual photon energy and range of six electron energies from 4 to 15MeV. We have physical wedges of 15°, 30° and 45°. We investigated the characteristics of physical wedge and virtual wedge angles 15°, 30° and 45° using 6 MV photon beam. Wedge factors were measured in water using an ion chamber for various field sizes. In case of virtual wedge device as upper jaws (X-axis) moves during irradiation. Measurements were done using Farmer type ionization chamber (PTW, Germany) and Unidos E electrometer. Surface dose were measured using Markus chamber (volume 0.055 cc), and slabs of various thickness.

Results and Discussion: We have studied depth dependence and field size dependence of both type of wedge i.e. physical and virtual at various wedge angles. For various field sizes, virtual and physical wedge factors were changed by maximum 2.4% and 3.6%, respectively. For various depths, virtual and physical wedge factors were changed by maximum 1.7% and 2.6%, respectively. Apart from studying depth and field size dependence, surface dose were also measured. Surface dose with physical wedge was reduced by maximum 18 to 20% (x-ray beam: 6 MV, SSD; 100 Cm) relative to one with virtual wedge.

Conclusion: We compared the characteristics of virtual wedge and physical wedge considering different parameters such as depth and field size. Virtual wedge having smaller depth dependence then physical wedge. Field size dependence of virtual and physical wedge was also analyzed. Further it was interesting to note that for physical wedge, surface dose was found to be less in comparison to virtual wedge at all wedge angles taken in our study.

   P-137: Evaluation and Dosimetric Comparison of OFF Axis Ratio for 6MV Photon in Various Wedged Angle Beams at Different Depths Top

Soniya Pal, Anoop Kr. Srivastava, S. Farzana, Mandvi Dixit, S. P. Mishra, Madhup Rastogi, Rohini Khurana, Rahat Hadi, Kamal Sahni, Ajeet Gandhi, Shantanu Sapru

Department of Radiation Oncology, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India. E-mail: [email protected]

Introduction: Wedge beams are utilised in conformal radiotherapy plan in various sites to obtain the dose conformity and homogeneity in the desired target volume (TV). The beam data plan generated in treatment planning system (TPS) by various algorithm calculates the off axis ratio to produce the isodose profile for planning. TPS generated isodose pattern and actual measured values should conform to avoid undesirable consequences in plan outcome. 3DCRT often uses suitable wedge angulations (5O, 10O, 20O, 30O, 45O, 60O) or any other suitable wedge to provide both tissue compensation and beam shaping for homogeneity and conformity. In the present study comparative evaluation of off axis ratio (OAR) has been made between isodose generate by superposition algorithm in TPS for wedge angles 5 O - 60 O at practical depth of 5, 10, 15 cm. The dosimetry data has been directly measured for all wedges for 6 MV photons and at practical depth in the solid water phantom using TRS-398 protocol. The OAR measurements have been made at 5 cm, 10 cm and 15 cm depths. The isodose pattern generated by TPS by superposition algorithm in the Xio TPS version 5.0 has been utilized for comparison. The study has been designed to compare TPS data as well as measured beam library for standardised the reliability of the TPS algorithm at various depths. Objective: The objective of this study is to verify the accuracy of isodose pattern generated by superposition algorithm for wedges of 5 O - 60 O at depth of 5, 10, 15 cm for 6 MV photons and compare the same with dosimetric data generated with the PTW dosimetric system in solid water phantom.

Materials and Methods: For this study PTW (Freiburg, Germany) 0.6cc ion chamber was utilized and measurement were carried out in SAD setup (100 cm) in solid water phantom at reference depth of 10 cm and off axis value for 6MV photon for 10x10 cm2 field size, both in negative and positive direction of central axis at 1 cm interval were obtained. The data were generated for open field as well as for 5O, 10O, 20O, 30O, 45O and 60O wedge angles which are most often used. Similarly, measurements were also carried out at 5 and 15 cm depth. A phantom of similar characteristic was generated in Xio version 5 for off axis values for the aforesaid wedge angles and depths using superposition algorithm was generated. A comparative chart was generated with measured and TPS generated OAR values which are detailed in [Table 1].
Table 1: Percentage variation in off axis ratio value at 5, 10, 15 cm depth between TPS and measured data

Click here to view

Results and Discussion: Accuracy of dosimetry and selection of algorithm for conformal planning is essential for the success of radiotherapy. It is thus imperative to verify quantitatively TPS data with actual dosimetry. It is further important to evaluate OAR in heterogeneous medium where charge particle equilibrium is lost which influence the profile generated. This study thus aims to develop a standard practice to verify the wedge beam profile and compare with the actual dosimetric data at the central axis at depth of 5, 10, 15 cm, the variations found are significant and the deviation at the edge of the field are larger. For this study measurements were carried out in homogeneous phantom and this work will be further extended to heterogeneous phantom with various algorithm and energies. The significance of this study is to generate the beam library and carry out a comparative evaluation for acceptance of TPS data for clinical practices. A variation 10-40% at field edge may have significance influence to obtain better conformity index or desired matched peripheral dose of 95% - 98%. The measure data and the comparison with TPS value will be represented in detail for various energy and depths.

   P-138: Statistical Analysis of Dosimetric Parameters of FF and FFF Photon Beam Top

Dwivedi Shekhar, V. K. Dangwal1, S. K. Kansal2, P. Sharma, R. Singh, M. K Mahajan

Department of Radiotherapy, Advanced Cancer Institute, 2Department of Physics, MRSPTU, Bathinda, 1Department of Radiotherapy, GMC, Patiala, Punjab, India. E-mail: [email protected]

Objective: The removal of the flattening Filter (FF) results in significant increase in dose rate and dose per pulse, softening of X-ray spectrum, reduction in the energy variation across the beam, decrease in head scattering, and hence reduces the leakage and out-of-field dose respectively. The purpose of this research work is to statistically analyse the dosimetric properties of a Linear accelerator with FF and without FF photon beams.

Materials and Methods: In this research paper, the radiation dosimetry and quality assurance of Varian TrueBeam Medical Linear Accelerator has been performed with the help of the dosimetry system. The protocols used for radiation beam data collection and acceptance testing are as accordance with the recommendation of international practice and guidelines such as AAPM (American association of Physicist) TG (Task Group)-142 &106 reports, TRS (Technical report series) -398 and AERB (Atomic energy regulatory board, INDIA) guidelines. The ionization chambers, radiation field analyser and water phantom are used for beam data collection and dosimetric measurements. Beam data measurement was performed for standard photon energies 6 MV, 10 MV flattening filter beam and 6 MVFFF, 10 MVFFF flattening filter free beams.

Results and Discussion: The dosimetric parameters evaluated for FF and Flattening filter free (FFF) photon beams are Percentage depth dose (PDD), percentage surface dose, percentage symmetry and percentage output factor. The dependent paired t-test analysis showed that the significant value of paired t-test for PDD, percentage surface dose and percentage output factor was less than 0.05; it means the removal of flattening causes a significant difference between the their mean values measured for FF and FFF photon beams. While the significant value of paired t-test for percentage symmetry was greater than 0.05; it means the removal of flattening causes no significant difference between the mean of percentage symmetry measured for FF and FFF photon beams. The Removal flattening filter changes various dosimetric parameters such as PDD, percentage surface dose and percentage output factor and therefore, all of them need to be redefined for FFF beam other than FF beam.

   P-139: Entrance Dose Measurement Using Silicon Diodes in External Radiotherapy Top

S. M. Pelagade, Laishram Suchitra

Department of Medical Physics, Gujarat Cancer and Research Institute, New Civil Hospital Campus, Ahmedabad, Gujarat, India.E-mail: [email protected]

Introduction: The aim of radiotherapy treatment is to deliver radiation dose to various malignant or non-malignant targets efficiently, accurately and safely. As the number of radiation incidences reported due to human errors, separate patient dose verification (in-vivo) is required during the actual treatment delivery in external beam radiotherapy (EBRT). In this paper, we will be discussing how we established in-vivo dosimetry (using p-type silicon diodes) technique by measuring various correction factors.

Materials and Methods: The measurements were performed on a Elekta Synergy linear accelerator, providing a 6 MV photon beam. Two identical diodes from IBA Dosimetry [EDP -10 /5143 and EDP -10 /5144 detectors (p-type silicon diodes)] with hemispherical build-up cap with DPD-12 (emX) electrometer were tested for entrance dose measurements. These diodes were calibrated against an ionization chamber (FC65) from Scanditronix Wellhofer in a 6 MV photon beam from a linear accelerator. In reference conditions, each diode was taped to a solid water phantom (dimensions: 30 cm x 40 cm x 40 cm) at a distance of 100 cm from the accelerator focus, in the center of an open treatment field measuring 10 cm x 10 cm and with gantry angle set to 0°. The ionization chamber was irradiated with the same treatment parameters at depth dose maximum, 1.5 cm below the phantom surface. Throughout the calibration and in vivo measurements, each diode was connected to a dedicated channel on a DPD-12 (emX) Scanditronix Wellhofer electrometer.

Results: In addition to the calibration factor, various correction factors accounting for non-reference conditions were determined.

Field Size Correction Factors: For 6-MV x rays, the field size correction factors for two identical diodes are very similar for the entire range of field sizes considered here. FFS for the EDP-10 / 5143 diode are 0.9108 for the field size of 3 x 3 cm2 and 1.0854 for the field size 40 x 40 cm2, while the FFS for the EDP-10 / 5144 diode are 0.9136 for the field size of 3 x 3 cm2 and 1.0853 for the field size of 40 x 40 cm2.

SSD Correction Factors: For 6-MV x rays, the FSSD for the EDP-10/5143 diode are 0.95013 at SSD of 80 cm and 1.04366 at SSD of 120 cm, while FSSD for the EDP-10/5144 diode are 0.95438 at SSD of 80 cm and 1.05125 at SSD of 120 cm. of 130 cm.

Angular Dependence Correction Factor: Angular dependence correction factor gives the dependence of diode for different angle between the central beam axis and the symmetry axis of the diode. Directional response of diode from -45° to +45° for both axial and tilt is less than 3 %.

Temperature Correction Factor, Ftemp: A linear increase of the diode signal with temperature is found. It is recommended that if Ftemp is smaller than 0.4% per °C, no temperature correction is needed for in vivo dosimetry. For each radiation field used in treatment a measured dose on the patient skin and calculated dose from treatment planning system were compared using a 5% tolerance. The maximum entrance dose deviation was observed to be 4.1 % for all the considered 10 cases.

Conclusion: In vivo entrance measurements have been proved to be a very useful as check for the dose delivered to a given patient. It can detect serious errors including an incorrect daily dose, treatment with the wrong beam energy, omission or use of the wrong wedge, and setup errors. A high precision can be obtained when the calibration and correction factors are carefully determined and applied to convert the diode signal in adsorbed dose.

   P-140: Out-Of-Field Radiation Organ Dose Measurements and Associated Secondary Cancer Risk Estimation in Patients Treated with Breast Cancer in Lebanon Top

Ibrahim Duhaini, Saad Ayoubi, Mahmoud Korek1

Chief Medical Physicist & RSO, Rafik Hariri University Hospital, 1Department of Physics, Beirut Arab University, Beirut, Lebanon. E-mail: [email protected]

Introduction: According to the National Cancer Registry in Lebanon for the years 2003 till 2007, more than 40 % of registered cancers in Females have Breast Cancer. According to the latest Report published by the NCR, Breast cancer remained the most relatively frequent cancer throughout the years (42-43%). The annual incidence rate for breast cancer has been increasing from 72/100,000 in 2005, to 87/100,000 in 2007. According to the World Health Organization 2003 Report, Breast cancer is the leading cause of cancer deaths worldwide in women under the age of 55 and more than one million women are diagnosed with breast cancer each year. Breast Cancer patients have different options of treatment depending on the age, type of cancer and other factors. These options include: Surgery, Chemotherapy, Hormonal Therapy, Radiation Therapy and other non-traditional therapies. In radiation therapy, our concern, the tumor in the Breast will be exposed to high-energy X-rays that destroy cancerous cells. It is often used as post-surgery therapy in an effort to kill any remaining undetectable cancer cells that may have invaded areas nearby the original site of the tumor.

Purpose: During radiation therapy of the breast, other organs in the body may receive a significant radiation dose that triggers a secondary cancer in these organs. In this study, the Out-of Field radiation doses will be measured in some organs and will be evaluated for the development of radiation induced cancer as recently defined by the International Commission on Radiological protection (ICRP).

Materials and Methods: An anthropomorphic phantom was used with Thermo- Luminescence Dosimeters (TLD) to physically measure organ doses when the breast is irradiated with a complete clinical dose prescription for cancer treatment.

Results: The measured organ dose values were done and found that the estimated risk factors on inducing cancer in these organs were very minimal compared to the standard values.

   P-141: Development of Real Time Abdominal Compression Force Monitoring and Visual Bio Feedback System Top

Tae-Ho Kim, Siyong Kim1, Dong-Su Kim, Seong-Hee Kang, Min-Seok Cho, Kyeong-Hyun Kim, Dong-Seok Shin, Hye Jeong Yang, Tae-Suk Suh

Department of Biomedical Engineering, the Catholic University of Korea, Seoul, Korea, 1Department of Radiation Oncology, Virginia Commonwealth University, VA, USA. E-mail: [email protected]

Introduction: Hard-plate based abdominal compression is known to be effective, but no explicit method exists to quantify abdominal compression force (ACF) and maintain the proper ACF through the whole procedure. In addition, even with compression, it is necessary to do 4D CT to manage residual motion but, 4D CT is often not possible due to reduced surrogating sensitivity. In this study, we developed and evaluated a system that both monitors ACF in real time and provides surrogating signal even under compression. The system can also provide visual-biofeedback.

Materials and Methods: The system developed consists of a compression plate, an ACF monitoring unit and a visual-biofeedback device. The ACF monitoring unit contains a thin air balloon in the size of compression plate and a gas pressure sensor. The unit is attached to the bottom of the plate thus, placed between the plate and the patient when compression is applied, and detects compression pressure. For reliability test, 3 volunteers were directed to take several different breathing patterns and the ACF variation was compared with the respiratory flow and external respiratory signal to assure that the system provides corresponding behavior. In addition, guiding waveform was generated based on free breathing, and then applied for evaluating the effectiveness of visual-biofeedback.

Results and Discussion: We could monitor ACF variation in real time and confirmed that the data was correlated with both respiratory flow data and external respiratory signal. Even under abdominal compression, in addition, it was possible to make the subjects successfully follow the guide patterns using the visual biofeedback system. The developed real time ACF monitoring system was found to be functional as intended and consistent. With the capability of both providing real time surrogating signal under compression and enabling visual-biofeedback, it is considered that the system would improve the quality of respiratory motion management in radiation therapy.

   P-142: Resolution Properties of Three Generations of Megavoltage Imagers in Radiation Therapy Top

K. Loot, O. Waletzko1, R. Rohn1, B. Spaan, A. Block2

TU Dortmund University, 1Clinic for Radiation Therapy at Klinikum Dortmund, 2Institute for Medical Physics, Klinikum Dortmund GmbH, Dortmund, Germany. E-mail: [email protected]

Mega Voltage (MV) imaging has evolved alongside radiation therapy, moving from film verification to electronic portal imaging devices (EPIDs) which nowadays offer support with patient positioning as well as dose verification. In this work, we will determine the spatial resolution properties of three EPIDs by measuring their modulation transfer function (MTF). The MTF maps the transfer of contrast (or modulation) as a function of spatial frequency. We measure the presampled MTF, which considers the entire detection process before the sampling of the signal. The phantom for MTF measurement consists of a tungsten plate with a polished edge, which is placed in front of the detector surface to create an input signal with step function characteristics. The measured edge spread function (ESF) is differentiated and Fourier transformed to yield the presampled MTF. We investigated the following three EPIDs:

  • System A: TheraView by Cablon Medical, fluoroscopic-optical system with CCD camera, linac: GE Saturne 43
  • System B: PortalVision aS500 by Varian, first generation flat panel imager, linac: Varian Clinac 2100
  • System C: PortalVision aS1200 by Varian, latest generation flat panel imager, linac: Varian VitalBeam

All images were acquired using 6 MV photons, source-to-phantom and source-to-detector distance were kept constant for all accelerators. The MTF analysis software was written using Mathematica (Wolfram Research) and results are depicted in [Figure 1]. The range of spatial frequencies for which the MV imaging systems show significant transmittance is limited to about 1 mm-1. The MTF of the camera-based system A exhibits lower values than that of the flat panel systems B and C for the entire spatial frequency range. The MTF drops to 50% at 0.16 mm-1 and reaches 20% at 0.35 mm-1. The first-generation flat panel imager B shows the highest values in the frequency range up to 0.4 mm-1. The MTF reaches 50% at 0.26 mm and 20% at 0.62 mm-1. The currently produced flat panel imager C shows the most balanced MTF, with moderate results for lower spatial frequencies but the highest values for spatial frequencies above 0.4 mm-1. The MTF shows 50% at 0.20 mm-1 and 20% at 0.80 mm-1. All three systems convert the high-energy photons into optical photons by means of a metal plate and a phosphor screen (scintillator). System A directs the optical photons to a CCD camera, whereas in the Systems B and C, the photons are detected by an amorphous silicon panel placed in direct contact with the phosphor screen. All three systems suffer from the spread of high-energy particles and optical quanta in the phosphor screen, leading to an overall low limiting resolution. The resolution of System A is deteriorated further by the spread of optical quanta in the camera lens. System C shows an optimized contrast transfer for higher spatial frequencies, caused by two alterations in the detector design: The thickness of the phosphor screen is reduced and the thinner scintillator allows less spreading of photons and improves the spatial resolution. System C also features an additional backscatter shielding to prevent irregular scatter from the support arm of the detector. Both modifications lead to the improved contrast transfer of 20% at 0.8 mm-1 spatial frequency. Our results document that there has been a steady improvement in the MTF with each successive imager generation. Further research will investigate the noise transfer properties of the system in a similar fashion. Our long-term goal is to correlate these physical quantities with the diagnostic image quality.
Figure 1: Presampled modulation transfer function of the three analyzed electronic portal imaging devices

Click here to view

   P-143: Development of New Non Metallic Artifact Free CT Marking Wire for Radiotherapy Top

S. Senthilkumar

Department of Radiotherapy, Madurai Medical College and Government Rajaji Hospital, Madurai, Tamil Nadu, India. E-mail: [email protected]

Introduction: In Radiotherapy computed tomography (CT) marker wires are frequently used to obtain accurate treatment field area for further processing. The placement of such markers is usually on the skin surface. CT marking wires should therefore exhibit the following features such as clear visibility, should not produce any artifacts and should be easy to use. Most commercially available CT marking wire are made of high-Z materials, which typically cause streaking artifacts, decreasing image quality of the subsequent reconstruction. In this work I have developed a new non metallic artifact free CT marking wire for External Beam Radio Therapy (EBRT).

Objective: The objective of this study was to fabricate indigenously non metallic artifact free CT marking wire which is alternative to lead wire.

Materials and Methods: A new type of non metallic CT marking wire were developed using various combination of low atomic number materials. The materials are in the powder form which can be modifiable to versatile shape and size according to the needs. Lead based CT marking wire and newly fabricated non metallic marker wire were used to evaluate the visibility of marker wire, CT number and artifact. Both the marker wire were placed in a 30x30x30 cm3 sheets of solid phantom (PTW) and imaged on a Toshiba multi slice CT scanner for quality analysis. The phantom was scanned using the similar imaging parameters such as 2 to 3 mm slice thickness, as commonly used in the simulation. For the visibility test I have done the CT scan topographic as well as in axial section. The CT artifact of marker were analysed using a J-image software.

Results and Discussion: On analyzing the CT scan of both the marker wire on phantom, it has been found that the newly fabricated marker wire has the equal visibility and almost no CT artifact when compared with the commercially available marker wire. The metallic marker wire produced bright streak artifact on the CT image but non metallic marker wire were not producing any streak artifact. The newly fabricated marker wire density has nearly equal to human bone density so, it appears as bright spot on CT without streak artifact. To conclude that the newly fabricated CT marker wire will be an alternative to the existing commercially available marker wire with almost no artifact and also cost effective, which can be used for the clinical CT simulation for all the anatomical sites and breast scar marking without producing any metal streak artifact.

   P-144: Residual Rotational Set-Up Errors After Daily Cone Beam Computed Tomography Image Guided Radiotherapy of Prostate Cancer Top

Soumya Roy

Department of Radiation Oncology, AMRI Hospital Ltd., Kolkata, West Bengal, India. E-mail: [email protected]

Introduction: Prostate/pelvis radiotherapy often requires a large field. An uncorrected rotational error could lead to a geometrical miss of the target volume for such extended field. This study was design to evaluate the residual rotational set up errors after using daily cone beam computed tomography (CBCT) based patient positional verification for prostate cases.

Materials and Methods: Total 608 sessions of CBCT for 22 patients receiving radiotherapy for locally advance prostatic and lymphnodal irradiation has been incorporated in this study.

Patients were placed in head in supine position with appropriate immobilization devices like knee rest and primary patient positing was done matching three LASER with the skin marking. Further a cone beam CT was acquired with scan parameters 120 kV & 650 mAs and further patients positional error was corrected An automatic rigid volumetric image registration was performed between the cone beam and planning CT scan. Matching was based on the soft tissue information available inside the volume of interest. Only translational degrees of freedom were allowed during online registration. The systematic and random errors (Σ & σ) attributed to the translational corrections were calculated as defined by Van Herk. Margins were calculated according to the equation 2.5 Σ+0.7 σ. The move was quantified in terms of the 3D vector composed of shift in the three translational directions: 3D vector = (a2+b2+c2), where a, b and c represent the lateral, longitudinal, and vertical shifts performed in the clinic. Translational shifts obtained in the clinic were retrospectively analyzed prior to each treatment fraction as well as the residual rotational errors remaining after translational correction. Average, maximum, minimum, standard deviation of systematic and random errors along each translational direction.

Results: The image quality of the CBCT images varied within and between patients and depended in particular on artifacts attributed to the volume of air present in the bowel bag. Nevertheless the image quality was adequate for visualization of bony structure while soft tissues were most often partly visible. The CBCT guided couch movement resulted in a mean translational 3D vector correction of 5.03 mm. Pitch was the most frequent source of residual rotational errors and resulted in shifts exceeding 6 mm in 50 fractions. The margins along vertical, lateral and longitudinal directions are found to be 7.3 mm, 6.8 mm, 5.6 mm respectively and the analysis shown in [Table 1]. Residual rotational error resulted in a target shifts exceeding 5 mm in 81 out of 608 sessions. Three patients out of total 22 patients alone accounted for 55 of these 608 treatment fractions. For 11 patients had shifts below 5 mm and 6 patients had 5 or less treatment fractions with such shifts i.e. 5 mm.
Table 1: The translational corrections made in the clinic (mm)

Click here to view

Conclusion: 18 of the 22 patients have none or few treatment fractions with target shifts larger than 5 mm due to residual error. In large treatment field even small rotational errors may result in substantial shifts at the edge of the treatment field. A setup margin (CTV to PTV margin) of 7 mm was sufficient to take into account residual set up errors in majority of the cases. In general, variation in pitch rotation was larger than yaw and roll rotation, which is in agreement with previous reports as well. Higher pitch rotation attribute to the fact that pitch positioning is difficult is using skin markers. However, three patients display a significant number of shifts suggesting a more systematic set up error.

   P-145: Determination and Evaluation of Intra Fractional and Set-Up Changes During Radiotherapy to the Cervical Carcinoma Using Cone Beam Computed Tomography Top

Pankaj Pathak, Rajesh Kumar, Praveen Kumar Mishra1, Narendra Birbiya, Manisha Singh2, Pankaj Kumar Mishra2

Department of Radiation Oncology, BIMR Hospitals, 1Department of Radiation Oncology, G.R. Medical College, 2Department of Applied Physics, Amity University, Gwalior, Madhya Pradesh, India. E-mail: [email protected]

Aim and Objective: To confirm the accuracy of the location of the Fudicial markings in relation to the actual isocentre of the irradiated volume due to Intra-fractional & Set-Up changes in Cancer Cervix with the help of Cone Beam computed Tomography (CBCT).

Materials and Methods: 15 patients of Cancer Cervix were treated by Intensity Modulated Radiotherapy (IMRT) in 25 fractions to a median dose of 50Gy @ of 2Gy/#. The CT scans acquired for verification were registered with simulation CT scans. The target volumes (GTV, CTV, and PTV) were contoured on all verification CT scans and compared to the initial GTV, CTV, and PTV in treatment planning system.

Results: We acquired Cone beam Computed Tomography (CBCT) for consecutive Three Days of 15 Patients of Cancer Cervix. The patients were treated with full bladder and empty rectum. We evaluated & tabulated the mean of all the shift acquired during CBCT of each patients in the form of [Table 1](a), (b) and (c) and the mean of means of shifts in Right -Left (RL), anterior-Posterior (AP) and Superior –inferior (SI) directions for each patients were determined & evaluated and tabulated in the form of [Table 2]. We found the mean of means in (RL): 0.6378 mm, mean of means in (AP): -1.1489 mm & Superior –inferior (SI) directions: -3.4732 mm respectively.
Table 1: Shifts obtained from consecutive three days cone beam computed tomography for 15 patients in right-left, anterior-posterior and superior-inferior directions for each patients

Click here to view
Table 2: The mean of means of shifts in right-left, anterior-posterior and superior-inferior directions for each patients

Click here to view

Conclusions: Organ motion and patient setup variation are two major concerns during radiation delivery for Cervix cancer because they lead to shift of the target from its reference frame in the CT treatment-planning. Depending on the treatment margins, uncorrected target shifts may lead to under-dosage of the Cervix, thus decreasing local tumor control, or over-dosage the Bladder & rectum, thus increasing rectal complications. Understanding the inter fractional target shifts due to interfractional target motion and daily setup error and their management becomes a critical issue for Cervix cancer radiotherapy. Image-guided radiotherapy is used for correcting interfractional organ shifts before radiation delivery with image guidance. We observed that consecutive three days CBCT is sufficient for Final Isocenter marking but Daily CBCT is recommended for every Cervical Cancers to reduce the radiotherapy errors to give accurate and precise treatment.

Acknowledgment: The Authors are thankful to the Department of Radiation Oncology, BIMR Hospitals, Gwalior, Madhya Pradesh, India and Clearmedi Healthcare Pvt. Ltd., Delhi, for the support.

   P-146: Evaluation of Six Dimensional Cranial Target Localization Accuracy in Two Different Immobilization System Using Exactrac Top

K. Tamil Selvan1,2, P. Ramesh Babu2, N. Arunai Nambi Raj3, K. Senthilnathan2, M. Sathiya Seelan1, G. Padma1, M. K. Revathy1

1Department of Oncology, Apollo Cancer Hospital, Hyderabad, Telangana, 2School of Advances Sciences, Vellore Institute of Technology University, 3Centre for Biomaterials, Cellular and Molecular Theranostics, Vellore Institute of Technology University, Vellore, Tamil Nadu, India. E-mail: [email protected]

Introduction: The precision and accuracy of the intracranial sterotactic positioning systems used for sterotactically applied radiation is critical for the success and safety of the treatment. Reducing geometric uncertainties helps in increasing therapeutic ratio. The patient setup errors can be obtained by comparing the images acquired during the treatment delivery with that of the planned position. By imaging several patients of a specific patient group regularly, the typical size of the systemic and random deviations for that group can be determined and based on the obtained values C; inical Target Volume (CTV) to Planning Target Volume (PTV) margin can be estimated.

Objective: The aim of this study is to determine the impact of immobilization on patient positioning in cranial radiotherapy using ExacTrac system. The six dimensional target localization accuracy between the dedicated sterotactic mask and conventional head mask was compared with the Exactrac X-ray 6D system (interfraction setup data).

Materials and Methods: Ninety one patients with cranial lesions were included in this study (34 sSterotactic radiosurgery (SRS), 27 Sterotactic radiotherapy (SRT) & 30 non SRS/SRT). For SRS and SRT patients dedicated sterotactic mask was used and the initial positioning to isocenter was done by Exactrac system using infrared positioning array. For all the other patients conventional head mask was used and alignment to isocenter was manually done with the external fiducial markers and lasers. Exactrac image-guided positioning system is utilized to obtain daily translational and rotational patient positioning drift from intended (planned) position. The 6D setup data is analyzed to obtain population mean, systemic and random errors in all the three scenario. Obtained systemic and random errors were used to derive CTV to PTV margin.

Results and Discussion: In SRS the population mean setup errors were 0.48, 0.56 and 1.28 mm in the lateral, longitudinal and vertical translational dimensions and 0.26°, 0.60° and 0.08° in the roll, pitch and yaw rotational dimensions. The margin requirements in translational directions ranged from 1.6 to 3.5 mm based on Van Herks and Strooms margin recipes. The margin requirements in rotational dimensions ranged from 2.2 to 2.8°. In SRT the population mean setup errors were 0.14, 0.62 and 0.98 mm in the lateral, longitudinal and vertical translational dimensions and 0.12°, 0.43°and 0.02° in the roll, pitch and yaw rotational dimensions. . The margin requirements in translational directions ranged from 1.7 to 3.9 mm based on Van Herks and Strooms margin recipes. The margin requirements in rotational dimensions ranged from 2.1 to 2.9°. With 3clamp head mask the population mean setup errors were 0.63, 0.12 and 0.91 mm in the lateral, longitudinal and vertical translational dimensions and 0.50°, 0.17° and 0.04° in the roll, pitch and yaw rotational dimensions. The margin requirements in translational directions ranged from 4.4 to 6.2 mm based on Van Herks and Strooms margin recipes. The margin requirements in rotational dimensions ranged from 3.1 to 4.4°.

Conclusion: In this study, we have evaluated the setup deviations observed during treatment positioning with two different immobilization systems. Further, we could validate the PTV margin requirements. The results show that there is a significant reduction in the target positioning errors with the dedicated sterotactic mask as compared with conventional cranial mask. With daily exactrac image guidance one might expect similar outcomes for both the immobilization system but due to residual errors and system limitations, dedicated sterotactic mask provides better target localization accuracy.

   P-147: Absolute Dose Verification of FFF Beams Using Ion Chamber and Optically Stimulated Luminescence Dosimeters with Cirs Electron Density Phantom for Anisotropic Analytical Algorithm and Acuros XB Algorithms Top

Vaibhav Mhatre, Shaju Pilakal, Arjun Mengal, Sandip Patil

Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital and Research Centre, Andheri West, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Aim of this study was to measure the absolute dose for AAA and Acuros XB dose calculation algorithm using farmer chamber and optically stimulated luminescence dosimeters (OSLD) for 6X and 10X FFF beams with CIRS electron density phantom (EDP).

Materials and Methods: Recently we installed Edge linear accelerator at our Institute first of its kind in India. The 6X and 10X FFF photon beams was investigated in this study. The CIRS EDP with various tissue equivalent plugs (lung exhale, lung inhale, liver, breast, muscle, adipose, bone) was used in this study. The EDP has 17 holes to hold different types of tissu-equivalent inserts. Each cylinder-like (they are not exactly cylinders – the diameter on one side is slightly smaller than the other side) insert is about 3 cm in diameter and about 5 cm in length. Nine inserts are in the small inner ring section and the other 8 inserts are in the outer ring section as shown in [Figure 1]. Only the 8 inserts on the inner section were investigated in this work. The absolute dose was measured using farmer ionization (0.6 cc) chamber (PTW) and OSLD's. The In-Light nanoDots OSLD system from Landauer was used for this study. The Optically-Stimulated Luminescence (OSL) dosimeter with aluminum oxide doped with carbon has been extensively used to monitor personal occupational radiation dose and the use of OSL dosimeters for dose measurements at therapeutic level in the last few years. All plans were created in Varian Eclipse treatment planning system (TPS) v.13.6 with one single AP field and calculated using Anisotropic Analytical Algorithm (AAA) and Acuros XB (AXB) algorithm for 6X and 10X FFF beams with gantry and collimator 0° on Edge Linear Accelerator. A dose of 200 cGy was prescribed at a depth of 6 cm for all plans with a field size of 5x5 cm. To measure the actual dose delivered to the prescription point, the individual plans were delivered to treat the EDP as shown in [Figure 1]. The MU's delivered were defined by the related treatment plans and the dose was measured using farmer ion chamber and OSL dosimeters. All measured doses were compared with calculated doses from treatment plans.
Figure 1: Absolute Dose measurement using Ion Chamber and optically stimulated luminescence dosimeters with CIRS Electron Density Phantom

Click here to view

Results: The absolute dose for 6X FFF and 10X FFF beams for AAA algorithm was ± 5 % as compared to Acuros XB was within ± 3% for both ion chamber and OSLD's. [Figure 2] shows the variation of absolute dose for farmer chamber and OSLD's for both the energies.
Figure 2: Histogram of percent variation for 6X FFF and 10X FFF beams using optically stimulated luminescence dosimeters and Ion chamber.

Click here to view

Conclusion: This study demonstrated that the dose calculation with Acuros XB algorithm for FFF beams can reach an accuracy of ± 3% considering the uncertainty of ion chamber and electrometer. Furthermore, we found that the Acuros XB was superior in Bone and lung inserts when compared against AAA algorithm.

   P-148: Relationship Between Dose–Volume Histogram and Overlap Volume Histogram of Rectum in Prostate Cancer Treatment Plan Top

Gipson Joe Anto, K. R. Sivaramakrishnan, Bojarajan Perumal, Kumar Raja Gattamaneni, Girish Kumar Chegu

Philips Innovation Campus, Bengaluru, Karnataka, India. E-mail: [email protected]

Introduction: Recently, radiation treatment plan prediction is emerging as new area of interest for many researchers. Radiotherapy plans are predicted based on many parameters. One of them is Overlap Volume Histogram (OVH). The OVH describes the fractional volume of the structure of an OAR that is within a specified distance of a target.

Objective: Objective of this study is to find relationship between Overlap Volume Histogram of Rectum in Prostate cancer and corresponding DVH in treatment plans.

Materials and Methods: Study is performed in 5 Prostate cases prescribed with a dose of 78Gy. Released version of Pinnacle Radiation Treatment planning system is used for the study. Auto Planning feature of Pinnacle Treatment planning is used which would eliminate the subjectivity of Planning. Same treatment Technique is used in Treatment planning for all 5 cases. OVH of Rectum is calculated for five cases with the Target volumes. The calculation of the OVH can be thought of as two steps – Uniform expansion and contraction of the target: (1) Target expansion: We first uniformly expand the target with a distance of a mm in all directions. The overlap volume between the expanded target and OAR is then calculated. The expansion with a mm is repeated until the expanded target fully encompasses the OAR, in which situation the overlap volume is the volume of the OAR. Calculation of the overlap volume between the expanded target and OAR is also repeated after each expansion. (2) Target contraction: The target is uniformly contracted with a distance of a mm in all directions. Such contraction is repeated until there is no overlap between the contracted target and OAR. During each a mm contraction, the overlap volume between the contracted target and OAR is calculated. The curve resulting from the target expansion and contraction is the OVH that characterizes the relative spatial configuration of the two objects. DVH is obtained from the plan generated by Auto planning tool.

Results and Discussion: A trend analysis is performed on the OVH s and DVHs of five cases. It is observed that there is a definite relationship between OVH and dose to the OAR, Rectum in our case is reflected in the DVH. If the expansion distance required is higher to completely cover the rectum lower is the dose to OAR. In OVH at a definite expansion distances if the curve is steep it is difficult to spare the OAR and vice versa. This relationship between OVH which can be obtained without even placing a beam and Dose to OAR can be exploited for plan prediction and would enable the planner to squeeze the dose to OARs.

   P-149: Indigenously Developed Monitor Unit Calculation Software “Mucal” for Verification Of 2D and 3D Treatment Plans Top

R. Holla, Amal Jose, B. Pillai

Department of Medical Physics and Radiation Safety, Amrita Institute of Medical Science and Research Center, Kochi Amrita Vishwa Vidyapeetham, Amrita University, Kochi, Kerala, India. E-mail: [email protected]

Introduction: The basic requirement of radiotherapy clinical software incorporates verification of the treatment plans. A software program, “MUCAL”, has been developed to perform an independent monitor unit calculation and compare it to the monitor unit calculated from the XiO (Elekta Medical systems, India) treatment planning system. The software helps to import treatment plans from the XIO treatment planning system and uses basic algorithms for dose calculation and evaluates the monitor unit on a distinct platform.

Objectives: In radiation therapy it is mandatory to verify the Monitor Units calculated by the planning system by a secondary dose calculation algorithm. There are several commercial solutions for performing this activity. We created an independent software “MUCAL” using MATLAB software platform that calculates and compares the monitor units calculated by XiO treatment planning system.

Materials and Methods: The Graphical User Interface that extracts the Beam Entry Point, Dose Specification Point, MLC Leaf Positions, SSD, number of beams etc, from DICOM treatment plan and performs the dose calculation. Percentage Depth doses, Collimator and Phantom scatter factors for several field sizes of Linac for 4 MV, 6 MV, 15 MV Photons and, 6 MeV, 8 MeV, 10 MeV, 12 MeV and 15 MeV electron energies were initially fed in to the generated software MUCAL. The software has the capacity to import MLC files from TPS and any other DICOM systems for performing the 2D dose calculations accurately. It also has the feature to enter the beam input parameters directly and calculate the dose and MU as 2D treatment planning system. DICOM files of several patients have been imported for calculation and compared the variation with TPS Monitor Unit.

Results: The mean deviation in the Monitor unit calculated by the XiO Treatment Planning system to the MUCAL software is found to be less than 5%. The developed software automate the entire process of secondary dose calculation check which improves the efficiency of the department.

   P-150: Dependence Of Tissue Inhomogeneity Correction Factors On Tissue Phantom Ratio (TPR20,10) Top

M. Akhtaruzzaman, P. Kukolowicz1

Faculty of Physics, University of Warsaw, 1Department of Medical Physics, Maria Skłodowska-Curie Memorial Cancer Centre and Institute of Oncology, Warsaw, Poland. E-mail: [email protected]

Introduction: Commissioning of the treatment planning system includes the accuracy of dose calculation in the inhomogeneous absorber. Several results of measurements of inhomogeneity correction factors (CFs) have been published. However, a dependence of CFs on beam energy may preclude such results from being applied to the general user's beam. The aim of the study was to assess the dependence of CFs on the photon beam energy.

Materials and Methods: CFs were calculated with the Batho method for several slab geometries comprising lung of 0.25 g/cm3 and water of 1.00 g/cm3. The CFs were calculated for 6MV (TPR 20/10 = 0.67±0.001) and for 15 MV (TPR 20/10= 0.76±0.001), k = -3, - 2, -1, 0, 1, 2, 3. All calculations were performed in the region were charged particle equilibrium exists.

Results: Changes of CFs of less than 2% were observed across the considered energy ranges. With a change of the TPR20,10 of 0.01, both for 6 and 15 MV at a depth of 5 cm below the lung; and lung thickness of 3, 5 and 8 cm, for field size of 10x10 cm2, the change in CF never exceeded 2.4%. The dependence of changes of CFs on TPR20,10 were 1.74% and 1.2% for field size of 5x5 cm2 and 20x20 cm2 respectively. Comparison of 42 6 and 15MV linear accelerators installed in Poland showed that the maximum differences of TPR20,10 for 6 MV and 15 MV were 4.2% and 2.2% respectively.

Conclusion: A linear dependence of CFs on energy were obtained. The smaller is the field size and deeper is the point of interest below lung the larger dependencies on energy were observed.

   P-151: Fluence Reconstruction for Rapidarc Treatment Plans Top

Rose Kamal, Gaganpreet Singh, Arun S. Oinam1, Vivek Kumar

Centre for Medical Physics, Panjab University, 1Department of Radiation Therapy, Regional Cancer Centre, PGIMER, Chandigarh, India. E-mail: [email protected]

Introduction: EPID verification of dose, 3D reconstruction of dose, various verifications of treatment plan. etc demands for the fluence data. The primary beam fluence information is not directly available for rapid Arc treatment plans in Eclipse Treatment planning system in contrast to IMRT treatment plans.

Objective: The aim of the study is to reconstruct primary beam fluence for RapidArc treatment plans from its DICOM beam parameters and treatment delivery records i.e. dynalog files and to validate the reconstructed fluence.

Materials and Methods: Eclipse treatment Planning system (v 11.0.31) is used to generate the RapidArc plans. A Medical Linear Accelerator of Varian Medical Systems, Palo, Alto, CA equipped with 120 multi leaf collimators is used to deliver the treatment plan. The DICOM-RT files of the patient are exported and the information related to beam parameters is extracted using MATLAB® software version R2008b (The MathWorks, Natick, MA). The fluence is reconstructed from extracted data of beam parameters for each gantry angle. The other set of fluence is again reconstructed from recorded dynalog files and validated against the fluence reconstructed from beam parameters. Gamma analysis between the reconstructed fluences is done using indigeneously built software.

Results and Discussion: The reconstructed fluence from both DICOM-RT file and dynalog files as shown in [Figure 1], also passes the gamma criterion of 1% dose difference and 1 mm distance to dose agreement tolerance limits for 95% bixel population. The fluence data reconstructed can further be used for 3D dose reconstruction to model an indigenous dose calculation algorithm and verification of delivered dose.
Figure 1: (a) Reconstructed fluence from beam parameters, (b) reconstructed fluence from treatment delivery records

Click here to view

   P-152: Effect of CT to ED in radiotherapy Treatment Planning with Algorithms Available in CMS XIO Treatment Planning System to Verify Inhomogeneity Correction Top

Suman Kumar Putha, Challapalli Srinvias, B. M. Vadhiraja1, Raghavendra Holla2, Dilson Lobo, P. U. Saxena, Sourjya Banerjee, Dinesh Pai Kasturi

Department of Radiotherapy and Oncology, Kasturba Medical College Hospital (An Associated Teaching Hospital of Manipal University), Mangalore, Karnataka, 1Department of Radiation Oncology, Manipal Hospital, Bengaluru, Karnataka, 2Department of Medical Physics and Radiation Safety, Amrita Institute of Medical Sciences, Kochi, Kerala, India. E-mail: [email protected]

Purpose: The aim of this study to verify the effect of CT to ED in radiotherapy treatment planning using available algorithms in Elekta CMS XiO treatment planning system (TPS) for inhomogeneity corrections.

Materials and Methods: Gammex Computed tomography electron density phantom is used to generate the CT to ED curve with high speed GE CT scanner. Two sets of CT to ED files were generated with and without the presence of water medium. Dose calculations were performed with CMS XiO with three inhomogeneous phantoms (comprising combination of water, lung and bone equivalent slabs). Three inhomogeneous phantom combinations were considered to mimic the homogenous (water equivalent), lung equivalent and bone equivalent tissues. CMS XiO treatment planning system is used for dose calculations with different field sizes (5×5, 10×10, 15×15 and 20×20) using Convolution, Superposition and Fast superposition algorithms to account inhomogeneous corrections.

Results: The dose calculations were over estimated by Convolution algorithm with mean deviation of -5.8, -3.2 and 2.1 in Phantom A, Phantom B and Phantom C respectively compared to Superposition and Fast superposition algorithms. The percentage variation of 0.2, -0.5 and -0.2 was observed among the with A, B and C phantoms using the CT to ED conversion files with homogeneous (water) medium and without homogeneous medium.

Conclusion: Superposition and Fast superposition algorithm dose calculations were superior compared to Convolution algorithm in CMS XiO treatment planning system. The deviation observed in the case two CT to ED sets with and without homogeneous medium observed to be minimal.

   P-153: Development of an Anthropomorphic Deformable Lung Phantom Top

Dong-Seok Shin, Seong-Hee Kang1, Kyeong-Hyeon Kim, Tae Ho Kim, Dong-Su Kim, Do-Kun Yoon, Tokihiro Yamamoto2, Tae Suk Suh

Department of Biomedical Engineering, Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, 1Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea, 2Department of Radiation Oncology, University of California Davis School of Medicine, Sacramento, USA. E-mail: [email protected]

Several deformable lung phantoms have been proposed for investigation of 4D imaging and radiotherapy techniques. However, the complex anatomy of the lungs and airways is not typically modeled. The purpose of this study was to develop an anthropomorphic deformable lung phantom and evaluate its characteristics. The phantom consists of: (1) an iodine-infused flexible urethane foam to simulate the lung parenchyma, (2) a 3D-printed deformable airway model, and (3) an in-house programmable motion platform. A 3D-printed airway model (diameter range, 1–16 mm) was developed using diagnostic CT image of a canine through image segmentation, computer-aided design modeling, and 3D printing. The 3D-printed airway model was used as a mold to cast the flexible foam such that the airway was surrounded by the foam. Repeat CT scans were performed at end-inhalation and end-exhalation phases over the time frame of 2 hours to quantify the density, motion, and deformation of the lung parenchyma, and to evaluate their reproducibility. Deformation vector fields (DVFs) were acquired using deformable image registration. The diameter variation of the airway was calculated to evaluate the airway deformation. The peak CT numbers of the parenchyma model were -798.2±3.3 and -710.6±3.3 HU on average at end-inhalation and end-exhalation, respectively as shown in [Table 1], which were comparable to the human lung density. Variations in the peak CT number were less than 7 HU. From visual inspection, the DVF was also similar to the human lung with greater displacements in lower regions than in upper regions. The length of deformation vector differences between the repeat scans was found to be less than 1 mm on average and data presented in [Table 2]. The mean difference of the airway diameter between two phases was 0.81±0.43 mm. The deformable lung phantom proposed in this study was found to mimic the human airways and lung parenchyma with reproducible density, motion, and deformation.
Table 1: Volume change and computed tomography numbers for the iodine-infused flexible urethane foam

Click here to view
Table 2: Length of deformation vector fields difference between reference data set and other data sets

Click here to view

   P-154: Review of Dosimetry for Total Skin Electron Therapy Using Different Detectors Top

Shantanu Kumar Mishra, C. M. Tambe, S. N. Kale, D. D. Deshpande

Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Total Skin Electron Therapy is a standard modality for the treatment of Mycosis Funcoides. It affects only a first few mm depth of skin over the entire body. This obviates the use of low energy electron beams, large field sizes of 80 cm width and 200 cm height at patient surface and large Focus to Skin Distances (FSD). In our institution, Modified Stanford technique is used to execute TSET.

Objective: The aim of this project is to review the dosimetry of TSET following AAPM TG-30 report and using TLDs and Radiochromic films.

Materials and Methods: A Varian Truebeam LINAC with 6 MeV HDTSe- mode for TSET having a dose rate of 2500 MU/min was used in the project. A wooden frame was designed with a slot for a Perspex scatterer/degrader of dimension of 110 cm × 195 cm × 2 mm. The calibration point is at a distance of 26 cm from the degrader. FSD is kept at 463 cm. Depth dose and profile measurements were done using PPC05 chamber and Solid water phantom (SP). Verification of PDD was done by sandwiching a Radiochromic film in SP. Profiles were verified using TLD with wax bolus for buildup. Angle of tilt was determined geometrically by superimposing 2 vertical profiles using FWHM and verified dosimetrically. PDD for 6 dual field was determined by placing film in a cylindrical wax phantom (WP). Absolute dose measurement was done at the calibration point (Umbilicus) using Roos chamber according to TG-30 and TRS-398 recommendations. MUs were delivered to get the prescribed dose for single dual field to the WP with TLDs attached in 3 positions 60° apart with 1.5 mm buildup. The same was verified in body phantom. Treatment skin dose was measured by exposing the WP to 6 dual fields with TLDs placed in all 6 positions and film wrapped around it with buildup.

Results and Discussion: Single TSET field has a mean energy of 4.2 MeV, most probable energy of 5 MeV at surface and X ray contamination of 1.5%. Uniformity for a single field in the central 60 cm × 160 cm region is 30% vertically and 5% horizontally which is below the recommended guidelines. To improve uniformity, the use of dual field becomes necessary. Angle of tilt calculated graphically, measured with TLD and determined dosimetrically are 15.5°, 16° and 17° respectively. However compared to other beam angles, at 17° tilt angle the best uniformity of 2% is obtained and considered appropriate [Figure 1]. The characteristics for both single and dual field are identical, both having dmax at 8 mm. Due to contribution of other beams the dmax for 6 dual field is 1.2 mm [Figure 2]. Measured absolute dose at Calibration point using dual field is 0.038cGy/MU. For a planned dose of 1.2 Gy for a dual field, the measured dose was 1.1 Gy. For prescribed skin dose of 3.6 Gy for 6 dual field, the measured dose was 2.92 Gy. This variation is due to uncertainty involved in the technique and needs to be explained to Physician in determining prescription dose. The ratio of Treatment Skin dose to Calibration point dose (B factor) was found to be 2.65 which is within the range specified in TG. Film result shows ±10% variation in uniformity around the surface and Dmax show a periodicity every 60° when exposed with 6 dual fields.
Figure 1: PDD curve of single field (black), 1 dual field (orange) and 6 dual field (blue). The dmax for 6 dual field is 1.2 mm compared to 8 mm of single or dual field.

Click here to view
Figure 2: Tilt angle verification using profiles of 15.5° (blue), 16° (orange), 16.5° (grey) and 17° (green). A ±2% of uniformity is obtained for 17° tilt angle in solid phantom.

Click here to view

Conclusion: Result shows a better uniformity of dose and hence can be used clinically.

   P-155: Radiation Dose to Adjacent Organs-At-Risk from Involved-Field and Involved-Site Radiotherapy for Lymphoma Top

Mazonakis, E. Lyraraki1, J. Damilakis

Department of Medical Physics, Faculty of Medicine, University of Crete, 1Department of Radiotherapy and Oncology, University Hospital of Heraklion, Heraklion, Crete, Greece. E-mail: [email protected]

Introduction: The conventional involved-field radiotherapy (IFRT) or the modern involved-site radiotherapy (ISRT) can be used for the management of Hodgkin and non-Hodgkin lymphoma above the diaphragm. Both radiotherapy techniques unavoidably expose the surrounding healthy tissues to ionizing radiation and they might lead to long-term complications such as second cancers and/or cardiovascular disorders.

Objectives: The aim of this study was to compare the radiation dose received by adjacent organs-at-risk from IFRT and ISRT for lymphoma.

Materials and Methods: Ten male patients with lymphoma in the region of mediastinum were referred for three-dimensional conformal IFRT in our department. The patients underwent a treatment planning computed tomography (CT) on a 16-slice scanner. The lungs, thyroid gland, esophagus, heart and spinal cord were defined as the organs-at-risk and they were manually traced on the patients' CT images. For each study participant, a new three-dimensional plan was generated for the ISRT technique in accordance with the guidelines of the International Lymphoma Radiation Oncology Group. The IFRT and ISRT plans were designed using 6 MV photon beams. The prescription dose was 30 Gy for all plans. The dose volume histograms derived from the above treatment plans were used to find the average radiation dose (Dav) received by the lungs, thyroid, esophagus and heart. The maximum dose (Dm) to spinal cord was also recorded.

Results: The planning target volume in all treatment plans received at least 95 % of the prescribed dose. The Dav of each organ-at-risk and the Dm of the spinal cord as calculated by the ISRT plans were significantly lower than those from the IFRT (p<0.05). The mean value of the Dav of the lungs, thyroid gland, esophagus and heart associated with IFRT was 1205±122 cGy, 910±770 cGy, 2193±477 cGy and 1686±586 cGy, respectively. The corresponding mean values due to ISRT were equal to 626±117 cGy, 70±47 cGy, 1358±198 cGy and 512±442 cGy. The mean Dm of the spinal cord from IFRT and ISRT was 3127±201 cGy and 3034±135 cGy, respectively.

Conclusions: The use of ISRT for lymphoma may significantly reduce the radiation dose to the adjacent organs-at-risk compared with the organ doses attributable to IFRT. The above dose sparing should be taken into account by both radiation oncologists and medical physicists in the choice of the proper irradiation technique.

   P-156: Comparison of Measured Dose Versus TPS Calculated Dose in the Indigenous Phantom Constructed with Stainless Steel (316L SS) Implant Top

Bhudevi Soubhagya N. Kulkarni, Gowtham Raj, Ravikumar Manickam1, M. Chandrasekhar2, Alok Kumar3, B. Naveen, Gururaj Deshpande, Vasant Harsur

VTSM Peripheral Cancer Institute, Branch of Kidwai Cancer Center, Kalaburagi, Karnataka, 1Kidwai Cancer Center, Bengaluru, Karnataka, 2Jawaharlal Nehru Technological University, Hyderabad, Telangana, 3Netaji Subhas Chandra Bose Institute, Kolkata, West Bengal, India. E-mail: [email protected]

Introduction: The outcome of radiotherapy depends on multiple factors such as accurate organ delineation, including the tumor volume, optimization of beam angles and intensities, voxel-based dose calculation and accuracy of dose delivery within the patient. The accuracy and resolution of the CT image set used for treatment planning is crucial. And the lack of it can fail all of these processes. Patients undergoing radical treatment of tumors in pelvic region with a steel implant leads to the CT artifacts which results in errors for treatment planning process. To evaluate the adverse effects on dose due to the presence of steel implants.

Objectives: To measure the dose at the interface between a hip metallic implants and surrounding area with an indigenous phantom at peripheral cancer hospital.

Materials and Methods: Materials for the implant phantom (IM-p) were chosen with the same goals as with previously developed phantoms: to caricaturist physical properties, such as density and attenuation coefficients, with simple manufacturing techniques. The IM-p was manufactured with the acrylic solid cylinder with openable 3 cylindrical holes of different sizes. The three acrylic openable wholes can be replaced with any materials of different density. In this study we have designed to insert three different size cylindrical steel rods. The steel used for the construction of phantom was 316L SS type which is commonly used in the orthopedic bone implants. For the point measurement the phantom was provided with the chamber holder where we can measure the TPS planned dose. The IM-p was scanned with the 3 acrylic cylinders on Philips Big bore computed tomography (CT) for oncology. The same phantom was scanned with the three steel implants inserted for the study. The Axial cuts were taken with matrix size of 512 × 512. The image sets were reconstructed with 2 mm slice thickness. The Philips big bore CT is provided with orthopedic metallic artifacts reduction (O-MAR) algorithm. These were transferred to the radiation therapy treatment planning workstation through digital imaging and communication (DICOM) to Eclipse (Palo Alto, USA Version 13.7) treatment planning system (TPS). A total of three image sets were exported one with acrylic inserts and second one with the 316L type inserts and the third one with the O-MAR corrected image set. A plan was constructed on both the image sets.

Results and Discussion: The phantom is under construction and the results will be presented during the conference.

   P-157: Surface Dose Variations in 6 and 10 MV Flattened and Flattening Filter-Free Photon Beams Top

Avtar Singh, Amit Saini, Shefali Pahwa, Ashok Kumar, D. D. Deshpande1, Tapas Dora, Amrinder Chhabra, Varinder Chhabra

Department of Radiotherapy, Homi Bhabha Cancer Hospital, Sangrur, Punjab, 1Department of Medical Physics, Tata Memorial Hospital, Parel, Mumbai, India. E-mail: [email protected]

Introduction: As the use of linear accelerators operating in flattening filter-free (FFF) modes becomes more widespread, it is important to have an understanding of the surface doses delivered to patients with these beams. Flattening filter removal alters the beam quality and relative contributions of low-energy X-rays and contamination electrons in the beam. Having dosimetric data to describe the surface dose and buildup regions under a range of conditions for FFF beams is important if clinical decisions are to be made.

Aims and Objectives: The purpose of this investigation was to evaluate and compare trends in surface dose for 6 and 10 MV flattened and FFF beams under conditions routinely experienced in radiotherapy treatments. These conditions were:

  • Variations in field size (square fields, sizes 3 × 3 to 40 × 40 cm2)
  • Variation in source-surface-distance (SSD) (70 to 110 cm)

Materials and Methods: An Elekta Versa H.D linear accelerator (Elekta) with a standard 160-leaf MLCi2 head has been used for measurements. The flattening filter is replaced with a 2 mm stainless steel plate that is used to shield out contamination electrons from the primary collimator. Measurements were taken in a slab phantom composed of 30 × 30 cm2 Solid Water equivalent slabs of varying thickness as shown in [Figure 1]. A thin window parallel plate chamber SNC350p (Sun Nuclear Corporation). Surface dose readings are therefore reported as relative surface dose (RSD) where RSD = dsurface /dmax.
Figure 1: Experimental setup for surface dose and buildup

Click here to view

Results: Field Size Variation: Surface doses are seen to increase almost linearly with increasing field size, albeit at a shallower incline for FFF beams than for the conventional [Figure 2]. At 6 MV the unflattened beam shows a slight increase in RSD at smaller field sizes and decrease at larger with equivalency at 15 × 15 cm2. At 10 MV there is again far less variation in the RSD with field size for the FFF beams, but the conventional beam generally exhibits lower surface doses [Figure 2]. The surface doses are of equivalent magnitude at a field size of 20 × 20 cm2. For the 6 MV beam, there is a variation in RSD of 24.1% in changing field size from a 3 × 3 to 40 × 40 cm2, compared to 14.4% for the FFF. At 10 MV these values are 28.75 % for 10 MV and 13.8 % for 10MVFFF.
Figure 2: Variation of surface dose with field size for flattened and flattening filter-free beams for jaw settings of 3 × 3 to 40 × 40 cm2: 6 MV and 10 MV

Click here to view

SSD Variation: At 6 MV there is little difference between the FFF and conventional beams, except near the treatment head where the FFF beams show a reduction in surface dose of up to 4% for large filed size 20 x 20 cm2 but for small filed size 5 x 5 cm2 is increased by 2% [Figure 3]. The 10 MV FFF beam again shows the same behavior as that of 6 MV beam. RSD is very stable between 90 and 110 cm SSD.
Figure 3: Variation of surface dose with source-surface distance for flattened and flattening filter-free beams for jaw settings of 20 × 20 and 5 × 5 cm2: 6 MV and 10 MV

Click here to view

Discussion and Conclusions: Removal of the flattening filter has been shown to have many potential benefits over con-ventionally filtered beams for the delivery of treatments techniques such as SRT, SBRT, and IMRT. The present study indicates that the surface doses from these beams are very similar to those experienced for conventional flattened beams, and are therefore unlikely to cause concern in a clinical setting.

   P-158: Commissioning and Dosimetry of Total Body Irradiation Top

Sabari Kumar, S. Sathiyan, M. Ravikumar, K. M. Ganesh, B. Shwetha, C. Varatharaj

Department of Radiation Physics, Kidwai Cancer Institute, Bengaluru, Karnataka, India. E-mail: [email protected]

Introduction: Total Body Irradiation (TBI) is a treatment technique that involves the irradiation of the whole body. Several disorders where the entire body requires treatment have been proven to respond to TBI, including Lymphomas, Leukemias and Aplastic Anaemia. In situations where an allogeneic bone marrow transplant (BMT) or stem cell transplant is prescribed it is common for such patients to undergo TBI in combination with chemical therapy as part of a pre-transplant cytoreductive conditioning process. Total Body Irradiation (TBI) is frequently used to destroy the bone marrow and leukemic cells, to immune suppress the patient prior to receiving a bone marrow transplant (BMT) or both. TBI differs in many aspects from the standard irradiation procedures, because the whole body, including the skin is the target volume. There are many factors that work to limit dose homogeneity when the total body is the target of irradiation. Such as irregularity of the irradiation volume, thickness variation, skin sparing effect of high energy radiation beam, significant amount of scatter radiation and dose measurement limitations etc,. Therefore beam calibration, radiation field analyze, in-phantom measurements and treatment setup are important considerations in the whole chain of TBI success.

Materials and Methods: In TBI, whole body is the target volume; the treatment field to entire patient body can be achieved at the extended distance from source (Geometric Divergence of Radiation beam) 400 cm. The dosimetry data at this SSD is little complicated due to phantom dimension limitation. The dosimetry data such as PDD, Beam Profile and Beam Calibration was analyzed at this extended SSD setup by considering different parameters of side scatter, beam modifier and dose rate etc,. The dose was estimated on the surface of Rando Phantom using OSLD and wax buildup.

Results and Discussion: Basic inverse square measurements showed around 17% deviation from calculated value of Standard SSD. The effect of side scatter on beam output was found negligible around 0.6%. The dose rate effect on the beam output was shown the significant large deviation of 4.5% in 6MV photon beam and 3.5% in 18MV photon beam. The deviation between the measured and calculated (using Mayneord Factor) PDD was 4.5% with 6MV photon beam and 4% with 18MV photon beam at the extended SSD. The beam modifier (1 cm Prespex sheet) placed at a distance of 15 cm from phantom surface is increases the surface dose to 95%. The humanoid Rando phantom was used for the dose verification. The dose was estimated on the surface phantom (Umbilicus, Head, Neck and Chest level) using OSLD. The deviation between the measured and calculated dose was within 4.5%.

Conclusion: This study shows that the standard dosimetric data is not adequate for the TBI treatment planning. It is mandatory to perform the necessary dosimetric measurement at the treatment distance before the treatment delivery.

   P-159: Dosimetric Considerations for Total Skin Electron Therapy: Our Initial Experience Top

Daicy George, V. Remya, P. Suresh Babu, Geeta S Narayanan1, S. Sowmya Narayanan

Departments of Radiation Physics and 1Radiation Oncology, Vydehi Institute of Medical Science and Research Centre, Bengaluru, Karnataka, India. E-mail: [email protected]

Introduction: Total Skin Electron Therapy (TSET) is undoubtedly an effective method for the treatment of cutaneous T-cell lymphoma often referred as mycosis fungoids. Since there are many challenges in the choice of treatment technique, its dosimetry and execution, there is a necessity of special attention towards all of the aspects.

Objectives: The objective of this study is to develop a TSET program in our institution and to review the dosimetric considerations of the same.

Materials and Methods:

Choice of Treatment Technique: Although phantom studies suggest patient rotation using platform provides best uniformity over body surface, six- dual- field technique (modified Stanford techinique) widely used with isocentrically mounted linacs was chosen for the ease of treatment execution. Clinac 2300C/D (Varian Medical Systems, Palo Alto, CA) equipped with the special procedure HDTSe- (high dose rate total skin electron mode, E=6 MeV) was employed to perform TSET irradiation. To achieve wider angular spread of dose distribution at patient surface, acrylic scatterer of 1 cm was placed 20 cm in front of the patient. The planned treatment distance from isocentre was 3.5 meters.

Characterization of Beam at Treatment Plane: PDD measurements were carried out using perspex slabs arranged at 20 cm from the beam scatterer for 4 MeV and 6 MeV. Measurements were also done without beam scatterer for 4 MeV electrons. The most probable energy was calculated from the practical range. Beam profile measurement was done by raising the platform height for the chosen energy. Parallel Plate chamber (PPC 40) was used for all the dosimetric measurements.

Determination of Hinge Angle: Appropriate hinge angle for the dual field was calculated to obtain best dose uniformity along the vertical axis of treatment plane. Measurements were carried out at 2700 and for different hinge angles varying from 150 to 200. Beam profile measurement was done for the selected hinge angle as well.

Patient Shielding: Eyes were shielded using lead equivalent spectacles 2 mm thickness. Toe nails and finger nails were shielded using combination of bolus and 5 mm Lead. Bolus was used to degrade the incident electron energy.

In vivo Dosimetry: In vivo dose measurement was done using Optically Stimulated Luminescence Dosimeter (OSLDs) and Metal Oxide Semiconductor Field Effect Transistor (MOSFETs) at calibration point and different regions.

Local Boost: Soles were found to be underdosed from in vivo measurement, hence require boost. Output was measured for Gantry 180o for 4 MeV electrons in a basin filled with water which acts as electron absorber. Local boost for scalp can be given in Table 90o and Gantry 270o position if dose measured by in vivo measurement is inadequate.

Results and Discussion: 6 MeV electrons at accelerator plane with degrader which produces 4 MeV electrons at the treatment plane was chosen for the treatment based on requisite penetration depth for the patient. Hinge angle was determined to be 17o. Symmetry of profile measured at treatment plane was found to be 3%. Dose rate was measured using parallel plate chamber at the calibration point in the treatment plane. Output for local boost for soles was also measured. Dose measured by in vivo measurements were found to be close to the prescribed dose.

Conclusion: It is important to consider the dosimetric characteristics of TSET for each patient and for different treatment setups. Dosimetric considerations of TSET using six- dual- field technique using linear accelerator is challenging yet possible with available resources and is an effective treatment modality for mycosis fungoids.

   P-160: The Response of Well Chamber to Pressure Variations at High Altitudes - A Monte Carlo Study for 169YB Source Top

Sridhar Sahoo, T. Palani Selvam, Arghya Chattaraj, D. Datta

Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Well-type ionization chambers traceable to national standards laboratory are routinely used to measure air-kerma strength of brachytherapy sources. During measurements, a temperature and pressure correction factor (KTP) factor is applied to account for the change of air density in chamber volume. Pressure, P is directly proportional to air density at a constant temperature, T (0C). P falls exponentially with height, h (m) and is given by the Barometric formula P=P0 exp(-Mgh/R (T+273.15)), where P0 is standard pressure (1013.2 mbar) at h=0, M is molecular mass (29 g/mol), g is acceleration due to gravity (9.8 m/s2), R is the universal gas constant (8.314 J/mol. 0K). For example, air density at Shimla (h=2276 m) is 0.94 kg/m3, which is about 78% of standard air density of 1.197 kg/m3.

Objectives: The KTP corrected normalized response (KTP, NR) of a Standard Imaging HDR 1000 plus well chamber to air density variations at high altitudes for 169Yb source is studied using EGSnrc and FLUKA Monte Carlo code. The 169Yb 4140 source model developed for HDR application is considered in this study. In addition, response of hypothetic well chamber made of graphite, copper and C-552 is also investigated.

Materials and Methods: The HDR 1000 plus chamber is 10 cm-dia and 16 cm-height, made of an aluminum foil on the butyrate inner wall, an aluminum collecting electrode and outer wall. Well chamber with investigated source is modeled in the CAVRZnrc user-code of the EGSnrc and FLUKA code. Simulations are carried out for air densities ranging from 0.862 kg/m3 (3048 m) to 1.197 kg/m3. These air densities cover cities in the world at different altitudes including Indian cities mentioned in [Table 1]. The energy response is obtained by multiplying the dose deposited in the cavity with the air density and normalized with respect to standard density. Assuming T=T0=22 0C, KTP = P0/P. The KTP, NR is presented in [Figure 1] for standard aluminum well chamber as well as for copper, C-552 and graphite materials for 169Yb source.
Figure 1: Graph represent the variation in the normalized response of chamber with air density for different chamber material.

Click here to view

Results and Discussion: [Table 1] presents the KTP, NR for Standard Imaging HDR 1000 plus well chamber (made of aluminum) calculated for different cities at high altitudes for 169Yb source. This response is about 1-3%, which is due to the range of electrons is higher than cavity dimension and few electrons will stop in the cavity. For air density 0.862 kg/m3, which corresponds to 3000 m height, the KTP, NR is 9% and 4% higher than unity for copper and aluminum chamber, respectively [Figure 1]. The response is about to unity for C-552 chamber and 1-2% lower than unity for graphite chamber. The uncertainties in the Monte Carlo calculations are in the range of 0.6 - 0.8%. The KTP, NR is higher for aluminum, copper chamber than graphite, C-552 chamber. This is due to (a) production of more electrons in copper and aluminum chamber and (b) higher photon cross section in aluminum and copper than for C-552 and graphite.
Table 1: Air densities of various cities having different altitudes and the variation in normalized response of aluminum chamber

Click here to view

   P-161: Decommissioning of HDR Brachytherapy Unit as Per Regulatory Requirement G-3 Top

Gayatri Sahu, Prakash Shinde, Sharmila Agarwal

Department of Radiation Oncology, Jaslok Hospital and Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Objective : Objective of this paper is to promote cost effective decommissioning of HDR brachy unit and safe disposal of decayed source as per AERB safety guideline AERB /RF/SG/G-3 on consenting process for radiation facility through eLORA. Decommissioning is a process by which radiation unit is taken out of operation in a manner that provides adequate protection to health and safety of the workers, public and environment and ensure the safe radioactive waste management practice.

Materials and Methods: Micro Selectron HDR 080.0 classic remote after loading brachy therapy machine having serial no. -38023 that uses Ir-192 source was installed at Jaslok Hospital & Research Centre Mumbai in 2005 with maximum capacity of 10 Ci by Nucletron India Pvt Ltd (Now it is Elekta medical system Pvt Ltd.). Machine was operational till 2014 and unit was used for treatment of carcinoma of cervix and for breast implants. HDR model classic reached it's end of guaranteed support period, after which source production for classic HDR was stopped. Decommissioning work executed by M/s Elekta Medical System India Pvt. Ltd in 2016. Decayed radioactive source need to be removed in to an approved transport container and the unit has to be decommissioned. Decommissioning may include dismantling and reuse of machine components. The disused radioactive source and any contaminated material need to be disposed off separately. Decommissioning may be initiated after getting NOC from AERB. Consent for decommissioning of HDR unit and permission for export of radioactive source to its original supplier was obtained through eLORA. Ir-192 source having activity of 0.0001Ci was transferred into the approved container; subsequently container was sealed and labelled as radioactive package. Labelling of the package, transport index and category of package were calculated by maximum radiation level at 1 meter from external surface of the packages. HDR Unit was checked for contamination after transfer of the source into the container and found no contamination. Machine was dismantled and unit and parts like source storage unit, head unit, power supply, and control unit were handed over to BME of Jaslok Hospital for scraping.

Following information was labelled on the surface of package:

  • Activity of source
  • Address of the consignor and consignee
  • Type of package
  • United nation no
  • Proper shipping address

Decayed source container was re-exported to original supplier with Transport Index, and container serial no. For radiation safety, TLD need to be worn during the source transfer and decommissioning process, radiation survey meter was also used to know the instant radiation level. Report on completion of decommissioning, safe disposal of source and personnel dose received during decommissioning operation was submitted to AERB.

Result: Decommissioning process was completed smoothly within the stipulated time period. The radiation protection survey conducted during the decommissioning process was found at background level. No contamination was found on head and source storage of the unit and at the end AERB was intimated about the decommissioning and safe disposal of source.

   P-162: A Brachytherapy Simulator: Top

Thayal Singh Elias

Division of Radiation Physics, Regional Cancer entre, Thiruvananthapuram, Kerala, India. E-mail: [email protected]

In Radiation Oncology, keeping the radiation sources of different activity (strength) into the tumour volume or body cavities is called Brachytherapy. For a complete Radiation Oncology centre, Brachytherapy facility is mandatory. Cancer of the uterine cervix is one of the major diseases treated by a Brachytherapy equipment. In this mode of treatment, applicator positional accuracy is very critical as the radiation dose exposure gradient is very steep. For treatment dose calculations using treatment planning software, the position of the treatment applicator is reconstructed using isocentric orthogonal radiographs. In this procedure, it is important to retain the position of the applicators from the time of applicator imaging until the end of the radiation treatment. Normally in the absence of a dedicated Brachy Simulator, the patient will be physically shifted/ moved from the applicator insertion table to Simulator or X-ray machine, then to the treatment cot/couch. These three/four physical transfers greatly affect the positional accuracy. To stop this error, this new system is designed. In this system, a C-Arm machine is integrated with the treatment applicator application table in such a way to take perfect orthogonal Radiograph and an automatic patient transfer mechanism to a trolley is provided. So in this system there is no need for any physical shifting of the patient. This provides an excellent treatment applicator positional accuracy for treatment planning and quick treatment execution leading to high patient comfort during treatment preparation and treatment execution. So it is expected to a good cancer growth control and cure.

   P-163: Determination of Bladder and Rectal Dose Using Mosfet and Radiochromic Film: A Phantom Study Top

A. Jeeva Bharathi, G. Bharanidharan, Prakasarao Aruna, J. Velmurugan, X. Sidonia Valas1, S. Purnima1, Thayalan Kuppusamy1, Singaravelu Ganesan

Department of Medical Physics, Anna University, 1Department of Radiation Oncology, Dr. Kamakshi Memorial Hospital, Chennai, Tamil Nadu, India. E-mail: [email protected]

Introduction: Dosimetry measurements are important for quality assurance in Brachytherapy sources with energy more than 100kev. Even 1.25MeV sources were used, hence the major challenge in brachytherapy is to verify the accuracy of dose distributions calculated by the treatment planning system. In vivo study of bladder and rectal dose in HDR is a tedious process and the patient safety is of higher concern. In this regard, measuring the bladder and the rectal dose is of prime concern with respect to intracavitary brachytherapy.

Objective: In the current study, it is aimed to determine the bladder and the rectal dose using MOSFET and radiochromic film in an indigenous phantom.

Materials and Methods: The measurements were carried out using 18 channels Microselectron - HDR. The doses were measured using Thomson Neilson MOSFET and EDT-3 radiochromic film. The calibrations of the radio chromic film were carried out for the Iridium source and the accuracy of the indigenous phantom was also determined using the HDR after loading system. The phantom has been designed which contains both the bladder and the rectum equivalent material and can accommodate the tandem and the ovoids assembly, which is normally used for brachytherapy.

Results and Discussion: Measurements were carried out by delivering the dose through the tandem and the ovoids in the phantom which contains the bladder and the rectum material. The detectors were placed over the bladder and the rectum material and the dose were delivered with respect to the reference points. The result shows that the dose received in the film is in good agreement with the planning system whereas for the MOSFET, it over estimates the dose.

Conclusion: The dose verification phantom for the rectum and the bladder was designed and their doses were estimated using MOSFET and radiochromic film, in which the radiochromic film and the MOSFET gives the dose which is in good agreement with the TPS.

   P-164: Surface Mould Technique for Meibomian Gland Carcinoma – A Case Study Top

G. Madhan Kumar1, C. Krishnappan1,2, C. Anu Radha2, J. Antony Paull1, Chirag Amin1

1Department of Radiation Oncology, Apollo CBCC Hospitals, Gandhinagar, Gujarat, 2School of Advanced Sciences, VIT University, Vellore, Tamil Nadu, India. E-mail: [email protected]

Introduction: Meibomian gland carcinoma is a very rare case, overall 1% or less of all cancers. It is about 3.2% among malignant tumors and 0.8% of all eyelid tumors. Meibomian gland carcinomas are typically found in women, most often in the seventh decade of life, and they usually are on the upper eyelid margin. The clinical appearance of Meibomian gland carcinoma is highly variable. They simulate such benign conditions as chalazion, blepharoconjunctivitis, keratitis, and other malignant or benign skin lesions. Many of the skin tumors have a predilection for the upper eyelid and have a yellowish appearance. Tumors at the eyelid margin commonly cause loss of eyelashes. Due to its surface irregularity it is a very challenging task for planning and delivery of radiotherapy. It is very difficult to choose the treatment technique for these types of tumors.

Objective: Aim of this study is to treat successfully of the Meibomian gland carcinoma which is located in the upper eyelid of the patient.

Materials and Methods: A male patient of age 42 years, is diagnosed with Meibomian gland carcinoma in his right upper eyelid has been taken for this study. According to the histopathological report, the size of the tumour was 2.5x1.5x1.1 cm with staging of pT3aN1. The tumour infiltrated to skeletal muscles also. In the CECT 2.2x1.0x1.5 cm sized mildly enhancing soft tissue density lesion is noted involving upper eyelid on the right side medially. And also the patient is having Metastatic carcinoma in right intraparotid lymphonode at the same side. Our team decided to treat this patient with surface mould brachy therapy. Surface mould is prepared with wax bolus and flexible implant catheters. The applicators were tagged with numbers to avoid the errors in treatment. A 5 mm thickness of the bolus is used to separate from the skin. We used four flexible implant catheters with spacing of 1 cm to cover the region and for better dose distribution. A CT scan is taken and from Vertex to the thorax. Planning and source optimization are done at Varian Brachy Vision 11.0 treatment planning system and the treatment was executed in Varian Gamma Medplus. Dose Prescribed for 50Gy in 25 fractions at every day one fraction. Metastatic carcinoma in right intraparotid lymphonode at same side treated with IMRT.

Results and Discussion: The patient has treated successfully. The progress of the treatment and the reactions were monitored on a weekly basis. The patient tolerated well and redness of the retina also minimal. The first three month follow-up shows the recovery of skin with hypopigmentation. Meibomian gland carcinoma is a malignant tumor and it tends to recur. Radiotherapy is quite effective in preventing local recurrences and controlling the long term control rates in these type of tumors. Treating with electron is another option for same patient. However to treat at the complex area of eyelid conventional surface mould brachy therapy has an edge over the electrons to save the vision of the patient and with minimal damage to the corneal. Taking call as brachy therapy as a choice to treat the Meibomian gland carcinoma is a good substitute for external radiation. The Brachy therapy technique is labour intensive with compared to External radiation. Even though it is labor it worthwhile to go for brachy therapy for the cases like an eyelid.

   P-165: Isolation Rooms for Radioactive Iodine (I-131) Therapy, Introduction Of Glass Window On The Wall For Patient Comfort And Better Ambience Top

Marwa Al Aamri, Ramamoorthy Ravichandran1, Naima Al Balushi

Department of Nuclear Medicine, Royal Hospital, Muscat, Oman, 1Department of Radiotherapy, Medical Physics Unit, Cachar Cancer Hospital and Research Centre, Silchar, Assam, India. E-mail: [email protected]

For administration of radioactive iodine for the treatment of differentiated cancer thyroid patients, activities ranging between 1.85GBq to 7.0GBq are used. Safety guidelines stipulate isolation of patients till their radioactive burden reduces to a level <10 μSv/h at 1 m. The construction of concrete rooms cleared by national regulatory authorities do not recommend presence of windows on the walls. Centralized air-conditioning with filters is incorporated in the design. Two isolation rooms originally designed for manual brachytherapy with Cs-137 and Ir-192, were being used for I-131 isolation work. Our experience over a decade showed many patients have phobia to stay in isolation rooms for more than 3 days, and hence many did not take the treatments. A necessity was felt to introduce glass window on the opposite side wall of entrance window, which had a service corridor with restricted entry, opening towards garden area. Commercially available lead glass used for x-ray CT scanner of size 1380 mm x 620 mm, of physical thickness 8.5 mm (2 mm Pb Equivalent) was fixed on the 0.35m thick concrete wall in both the rooms. The adequacy of protection offered by the lead glass was determined using a 600MBq I-131 capsule moved at a distance 50 cm away from the wall inside the room, and measuring transmission outside the room. An end window pancake type beta gamma survey meter with uncertainty ±15% was used for measurements. The measured values were normalized for 3.7GBq at 2m bed position in μSv/h. The obtained maximum exposure rate was 7.85 μSv/h, transmitted from the glass window, against 0.012μSv/h transmitted at full concrete wall level. As the patients provide shielding to the administrated activity, also the activity is progressively decreasing fast with an effective half life, the stray radiation levels will be decreasing outside, increasing the efficacy of protection. The patient's bed position is at lower level by 0.5m from the lower edge of the lead glass, so that during patient is in bed the stray radiation levels reduce further. The isolation rooms were handed over back after the present modification, with recommendations a) to have a cloth screen on the window inside the room for patient's privacy and b) to have a caution radioactive sign abstaining use of the service corridor by patients and relatives unless there is emergency. As there are no reports about such facility for isolation rooms, this report may be of value in health physics literature.

   P-166: Occupational Doses of Radiation Workers in Nuclear Medicine Department, Ministry of Health, Oman: A Dose Analysis Top

Sharifa Al-Kindy, Nadia Al-Isaee, L. S. Arun Kumar, Jamal Al-Shanfari

Department of Medical Physics and Radiation Protection Service, DGPEA, Ministry of Health, Muscat, Oman. E-mail: [email protected]

Use of ionizing radiation in the Sultanate of Oman is increasing with the proliferation of hospitals and clinics. The great benefits of increased and improved diagnostic services have improved the quality of life for those in Oman. The World Health Organisation in 2000 applauded the quality, efficiency and delivery of health care to the population and ranked the Oman's health care system eighth in the world.[1] The increased resources are clear from the statistics: in 1970 there were only 2 hospitals in Oman, in 2010 the number was 50 and with 172 health centres.[2] One of the balancing consequences of increased x-ray use in Oman is the increased radiation dose to the population. Medical radiation accounts for the majority of the manmade radiation dose to populations.[3] Use of radiation must always be according to the ALARP (as low as reasonably practical) philosophy so as to avoid unnecessary radiation doses and minimise the doses where required which in turn reduces the occupational exposure. During 2015, a total of 15,56,686 radiological procedures were performed in Ministry of Health (MOH) institutions. The corresponding number in 2000 was 799,452. This shows that there is about 95% increase in radiological examinations for the last 15 year period. This indicates that the population dose is on the rise as the radiological facilities are increasing in Oman which in turn increases the occupational dose of radiation workers. The occupational exposure of radiation workers of MOH hospitals were monitored by Thermo Luminescent Dosimeters (TLD's) which are dispatched to each location in MOH by post. We have developed an in-house dose management software - Centralised Dose Recording System (CDRS) for the management of dose records of Ministry of Health (MOH) radiation workers which manage TLD serial number allocation, issue to various hospitals/institutions, collection from respective hospitals/ institutions after wear period, dose assessment and monitoring, recording the doses and finally dispatching the dose reports to MOH hospitals/ health centres / institutions. Also, the same software will handle the individual dose (s) of each worker (s) and their dose history. Every month we are dispatching more than 1600 plus badges to 160 hospitals/ institutions of MOH throughout the Sultanate of Oman after tagging in CDRS. Thus we keep track of the TLD badges of each worker in every location of MOH on a monthly basis. Some of the above locations are very remote (few thousand kilometers away from the capital city- Muscat). In this study, we have analysed the dose pattern of radiation workers in the Nuclear Medicine Depts. of Ministry of Health for the ten year period 2006-2016. The range of whole body effective doses (Hp (10)) of the workers for the year 2016 is shown in [Table 1].
Table 1: Whole body effective doses of radiation worker

Click here to view

The total number of workers wearing WB badges is 47 and the total number of workers wearing Ring badges is 35.

Similarly the extremity doses for both left finger and right finger badges were evaluated for the 35 workers.

The total number of workers wearing Left Ring badges is 8 and Right Ring badges are 27 and data of extremity doses of the workers is presented in [Table 2].
Table 2: Extremity doses of radiation worker

Click here to view

It has been observed that workers in Nuclear Medicine receive relatively the same whole body effective doses compared to majority of the radiation workers of Ministry of Health and comparatively very low doses when compared to those in interventional radiology and cardiology depts. However, the extremity doses of the workers were found to be reasonably high as expected, particularly those who are involved with the hot lab and radiopharmacy operations. Further details will be discussed during presentation.

   P-167: Dose Calibrator Linearity Test Using I-131 and 18F-Fluro De-Oxy Glucose. Top

Radha Muthuswamy, T. Suresh, S. Amutha

Department of Radiotherapy, HCG Bharath Hospital and Institute of Oncology, Mysuru, Karnataka, India. E-mail: [email protected]

Dose Calibrators are devices used in radiotherapy to ensure that the dose delivered is what is intended. Dose calibrators are one of the most important and most frequently used instruments for the determination of activities in nuclear medicine. For guaranteeing a constant quality of the dose calibrators' measurements, constancy checks including the examination of the system linearity have to be performed regularly. Linearity test check confirms that, for an individual radionuclide, the same calibration setting can be used to indicate the correct activity over the range of use of that calibrator. We participated in 17th National Audit of I-131 Activity Measurements conducted by RSSD, Bhabha Atomic Research Centre.

Objective: The present study was aimed at performing the linearity test in dose calibrator at our Hospital using I-131 and 18F-Fluro de-oxy Glucose. We are using dose calibrator manufactured by COMECER.

Introduction: Dose calibrator is a gas-filled cylinder with a well in the center of the ionization chamber into which the radioactivity is placed. An ionization chamber is an instrument constructed to measure the number of ions within a medium. It usually consists of a gas filled enclosure between two conducting electrodes (the anode and cathode). Typically, highly pressurized Argon [18-Ar] gas, compressed to around 20 atmospheres is used to fill the ionization chamber radiation detector. When gas between the electrodes is ionized by any means, such as by gamma rays or other radioactive emission, the ions and dissociated electrons move to the electrodes of the opposite polarity, thus creating an ionization current which may be measured. A voltage potential can be applied between the electrodes; depending on the application. Ionization chambers are widely used in the nuclear industry as they provide an output that is proportional to radiation dose.

Materials and Methods: The test was performed using Dose calibrator manufactured by COMECER. The schematic diagram of a Dose Calibrator is shown in [Figure 1]. Sources used for the test were I-131 and 18F-Fluro de-oxy Glucose. The linearity test must be tested upon installation and at least quarterly thereafter as well as after repair. In this study we have used the Decay method.
Figure 1: Schematic diagram of a dose calibrator

Click here to view

Decay Method: This method involves a single radioactive source which is periodically measured over several days.

  1. Assay the I-131 activity to be used in a syringe or vial in the dose calibrator, and subtract background to obtain the net activity in millicuries. Record the date, time to the nearest minute, and net activity.
  2. Repeat the assay everyday about the same time.
  3. Convert the time and date information you recorded to days elapsed since the first assay as shown in [Table 1].
  4. The measured activities and the calculated activities are then plotted versus time graphically [Figure 2]. Label the vertical axis in milli curies to represent the measured activity and label the horizontal axis as Time elapsed since the first essay in days. Calculate the percent error for each activity level/time interval.
  5. Table 1: Deviations between experimental and theoretical activities for I-131 at different times and measurement windows

    Click here to view
    Figure 2: I-131 source activity decreases as a function of time

    Click here to view

    Use the formula:

  6. Repeat the same procedure for 18F-Fluro de-oxy Glucose. The results are shown in [Table 2]. The graph is as shown in [Figure 3].
Table 2: Deviations between experimental and theoretical activities for 18F-fluorodeoxyglucose sources at different times and measurement windows

Click here to view
Figure 3: F-18 source activity decreases as a function of time

Click here to view

Measurements carried out for 17th National Audit of I-131 Activity Measurements:

  1. Ensure that radionuclide selected in the display is I-131.
  2. Take 10 readings within 20 minutes, each time removing the source from the chamber and replacing it back into chamber for the next reading.
  3. Calculate Mean and standard deviation.
  4. Repeat the measurements on the next day at about the same time.

Discussion: The results of the study showed that the dose calibrator is working satisfactorily and has passed the linearity test. The graph plots for measured data perfectly fits the calculated data for both I-131 and 18F sources. The discrepancy between measured data and calculated data were within +4%. If the deviation is more than +10% then an investigation has to be done on the dose calibrator. Our Hospital Dose Calibrator showed deviation of -3% relative to BARC activity.

   P-168: Enhancing Radiation Safety and Patient Comfort Based on Analysis of Radiation Data at the Time of Discharge Of Radioiodine Therapy Patients Top

K. S. Shekhawat, Prakash Yadav1, Harshul Sharma1, J. K. Bhagat1, R. S. Lokhande

School of Life & Basic Sciences, Jaipur National University, 1Department of Nuclear Medicine, Bhagwan Mahaveer Cancer Hospital and Research Centre, Jaipur, Rajasthan, India. E-mail: [email protected]

Objective: To work out the radioiodine therapy plan by predicting hospital stay duration based on retrospective data of patient radiation level at discharge.

Materials and Methods: Radiation monitor readings of patient radiation level at discharge of 500 Cancer thyroid patients who have received radioiodine therapy at BMCHRC, Jaipur was analysed. The patient were categorized based on level of blood markers, residual tissue, nodal status, lung and bone involvement, 131-Radioiodine dose, duration of stay, etc. Statistical analysis was done using biostatics.

Discussion: The disease status and radioiodine dose amount play very crucial role for the planning and management radioiodine therapy patients. However, the level of radiation at the time of discharge can vary from patient to patient due to variation in absorption of oral radioiodine and biological half life of radioiodine in the patients. Averaging the values of Radiation monitor readings of patient radiation level at discharge can help in approximate prediction of duration of stay for various categories of patient. This can be helpful in scheduling the patients for radioiodine therapy.

Conclusion: The readings of patient radiation level at discharge can be helpful for better management.

   P-169: Performance Characteristics of Positron Emission Tomography Scanners Top

Hemant Kumar

Department of Radiodiagnosis, SMS Medical College, Jaipur, Rajasthan, India. E-mail: [email protected]

Medical imaging is the technique that uses the radiation as a tool to create visual representations of body interior for clinical analysis. Positron emission tomography (PET) is nuclear medicine functional imaging technique that introduced to observe metabolic processes in the body. PET provides the most specific and sensitive means for imaging molecular pathways and interactions in the tissues of man. In this technique small amounts of radioactive materials called radiotracers are introduced into body that emit positrons generate anti matter annihilation effect at 180 degree. Produced gamma rays can be detected by computer detector and produce functional image. The resulted image from PET shows bright spots on film reveals higher level of chemical activity and details about the function of tissue or organs. Significantly PET imaging shows physiological imaging, differentiate between malignant and benign tumor, tumor staging, pharmacokinetics of several novel antibiotics can be measured in human being etc. PET is also used to analysis in recurrent of various carcinomas. A major goal of the PET studies is to obtain a good quality and detailed radiological image of an object by the PET scanner. It depends on how well the scanner performs in image formation. There are several parameters associated with the scanner are critical to good quality image formation, which include spatial resolution, sensitivity, noise, scattered radiations, and contrast. These parameters are interdependent, and if one parameter is improved, one or more of the others are compromised.[1] In PET systems the clinical image is assumed to be linearly related to the activity uptake; because scatter adds a smoothly varying background to the image, it degrades the quantitative accuracy of the image and adds to the image noise, even when accurately estimated and subtracted.[2] There are many other performance characteristics that reflect a given aspect of a nuclear medicine PET imager. However, the Quantitative linearity and calibration is an important measurement for PET systems that aim to relate pixel values to activity concentrations.

Saha GB. Basics of PET Imaging – Physics, Chemistry & Regulations. Berlin: Springer; 2010.

Bailey DL, Humm JL, Pokropek AT, Aswegen AV. Nuclear Medicine Physics: A Handbook for Teachers & Students. Vienna: IAEA; 2014.

   P-170: Estimates of Entrance Skin Dose for Patients Undergoing Common Radiographic Examinations Top

S. C. Uniyal, S. D. Sharma1, S. Raghuvanshi

Department of Radiology, Himalayan Institute of Medical Sciences, SRH University, Dehradun, Uttarakhand, 1Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Diagnostic X-ray imaging is the largest contributor to total population radiation exposure from man-made radiation sources. This is attributed to better technology and growing usage of diagnostic x-ray imaging methods. Patient dose involved in a diagnostic X-ray examination is a function of several parameters such as performance of X-ray machine, type of image receptor and selection of exposure parameters. The International Commission on Radiological Protection (ICRP) recommends that the patient doses should be measured on regular basis to optimize patient protection. So under realistic conditions of exposure, patient dose should to be estimated and verified against the established national diagnostic reference level (NDRL). DRLs for radiographic projections are often expressed in terms of the entrance skin dose (ESD), which is a measure of the amount of energy imparted per gram of tissue at the entrance surface.

Objectives: The present study was aimed to evaluate ESD for common types of radiographic examinations and to validate the results against established NDRLs.

Materials and Methods: The study was carried out on 1545 adult patients (age > 18 years) undergoing 10 commonly performed diagnostic X-ray examinations viz., chest posterior-anterior (PA), chest anterior-posterior (AP), cervical spine AP, cervical spine LAT, abdomen AP, lumbar spine AP, lumbar spine LAT, pelvis AP, thoracic spine AP and thoracic spine LAT performed in five X-ray rooms. ESD per X-ray projection was estimated by using an indirect method using following expression:

ESD = Tube output (μGy/mAs) × mAs × (100/FSD)2 × BSF

Where FSD and BSF are focus-to-skin distance and backscatter factor respectively. Fixed focus-to-film distances (FFDs) of 180 cm and 100 cm were used for chest PA and rest of the X-ray projections respectively. FSD was calculated by subtracting patient thickness from the focus-to-film distance (FFD). Although values of BSF vary with X-ray beam qualities used for different radiographic projections, a single average value of 1.35 was used for the estimation of ESD in the present study. The output of each X-ray tube was measured by using a factory calibrated RaySafe Xi R/F detector from UnforsRaySafe AB, Billdal, Sweden.

Results and Discussion: Descriptive statistics of the obtained ESD data were presented in terms of mean, standard deviation, median and third quartile values. The lowest and highest average values of ESD were 0.29 mGy and 7.39 mGy for chest PA and lumbar spine LAT examinations respectively. For a given projection, the variation ESD was expressed in terms of the ratio of its maximum to minimum values. This ratio ranged from 5.05 for thoracic spine AP to 16.87 for chest PA X-ray examinations. The observed wide variation in the estimated ESDs for individual projections was attributed to the variation in patient thickness, operator specific selection of exposure factors and the radiographic technique used. The third quartile values of estimated ESDs were compared with respect to Indian NDRLs proposed in 2001 (Sasane et al.) and 2010 (Sonawane et al.). The majority of values were found smaller than the recommended NDRLs. The 3rd quartile values of the estimated ESDs were recommended as local/institutional DRLs.

   P-171: Our Experience with the Acceptance and Dosimetric Validation of Somatom Force Dual Head MDCT in the Royal Hospital, Oman Top

Ruqaia Al-Harthi, Munira Al-Kalbani, L. S. ArunKumar, Jamal Al-Shanfari

Department of Medical Physics and Radiation Protection Service, DGPEA, Ministry of Health, Muscat, Sultanate of Oman. E-mail: [email protected]

Introduction: Computed Tomography (CT) has revolutionized diagnostic imaging since its discovery in early 70's. In Oman; 70,353 CT examinations were carried out in the year 2015. The increase in CT examinations will eventually result in the increase of population dose and the consequent risk of cancer in adults and particularly in children. Here, we discuss and share our experience with the acceptance and dosimetric validation of second Dual Head Somatom Force MDCT installed in the Royal Hospital, Oman using Ministry of Health's radiation acceptance and quality assurance protocol, before handing over for routine patient care work.

Materials and Methods: The parameters measured included - scatter radiation, CTDI, Noise, CT numbers and Slice thickness. Scatter radiation levels were measured using perspexbody phantom and Victoreen NERO 8000 by connecting externally a 400 cc scatter chamber to it. CTDI was estimated using 100 mm pencil CT ion chamber along with NERO 8000, PMMA head and body phantoms. Weighted CTDI (CTDIw) and normalized weighted CTDI (nCTDIw) were estimated. nCTDIw was estimated for each tube separately and in the combined dual energy mode as well. Image noise, slice thickness and CT numbers were measured with AAPM CT performance phantom (Victoreen).

Results and Discussion: The scatter radiation was measured at different positions around the scanner. The results show that the radiation levels around the scanner are distributed based on the invers square law. The radiation levels at the rear side of the gantry are little more than the front side due to the attenuation of radiation through the gantry. The normalized weighted CTDI (nCTDIw) values for head and body phantoms were measured for various kVp's and collimations for each tube separately and in dual energy mode as well. All results were analyzed, which were in good agreement with manufacturer's values. The CT number insert in the AAPM performance phantom had Polyethylene, polystyrene, nylon, polycarbonate and acrylic with HU -68, -24, 92, 102 and 120 respectively. The CT number was measured for various kVp's for each tube separately and in dual energy mode as well. The measured CT values were in good agreement with the quoted CT numbers. The image noise was analysed by measuring the mean CT number of the ROI and standard deviation. The image noise was analysed for various kVp's for each tube separately and in dual energy mode as well. All measurements were within the limit. Different slice thicknesses were set and measured in the AAPM performance phantom at different kVp's for both tubes. The measured slice thickness were in good agreement with the set values.

Conclusion: In this study we have tried to validate the standard QA protocol of Ministry of Health for CT scanners in this DE MDCT as well. Results showed that the measured parameters were in close agreement with the manufacturer's specs. Surveys shown that CT scanners operating at correct parameters deliver optimal radiation exposure to patients whereas dose to the patients will be significantly affected if not set properly. Thus a well performed QA programme in accepting and validating CT scanners will yield good quality scans which in turn delivers an optimal dose to the patients undergoing CT investigations.

   P-172: Estimation of Entrance Skin Dose During Abdominal Diagnostic X-Ray Examinations Using Optically Stimulated Luminescence Dosimeter Top

M. Kumaresan, Anuj Soni1, R. Kumar1, A. Chaubey, S. Kantharia

Department of Radiology, Medical Division, Bhabha Atomic Research Centre, 1Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Aim: The aim of this study was to use the indigenously developed optically stimulated luminescence (OSL) dosimeter for estimation of entrance skin dose during abdominal diagnostic X-Ray examinations and evaluate the work practice on the basis of radiation safety point of view.

Materials and Methods: The α-Al2O3:C OSL dosimeter used in this study was developed in Bhabha Atomic Research Centre, Mumbai. The α-Al2O3:C OSL pallets used were having diameter of 0.7 cm and thickness of 0.014 cm and are prepared by mixing the α-Al2O3:C powder of grain size (75-100 μm) between and Teflon in 1:3. OSL disc were sealed in a black light-tight polythene pouch to make it light insensitive. This pouch was kept on the patient's body in the center of the field of the radiographic projection. After experimental irradiation, the OSL discs were read individually using RISO TL/OSL reading system TL/OSL-DA-15 which has a cluster of 42 blue light emitting diodes (α =470 ± 30 nm) for stimulation. A band pass UG1 filter which prevents the scattered blue light from reaching the photomultiplier tube was used. The OSL was recorded at a power of 40 mW-cm2 for 60 s. The background data from control cards (dosimeters) were subtracted from the irradiated dosimeters to evaluate the net dose. The dosimeters were calibrated in RSS, RSSD BARC for the energy 80 kV. The Shimadzu Q-Rad 50 x-rays unit with Konica Minolta DR system was used in this study. The exposure parameters (kVp, mAs, focus to skin distance, field sizes) of the studied patients were recorded. The kV, mAs, ranges from 60 - 70 kVp, 80-160 mAs, respectively. Focus to imager distance and field size was set as 110 cm and 40 x 35 cm2 respectively. All measurements were performed in bucky mode. ESD of 53 patients of different age and sex were measured.

Results: Measured average entrance skin doses during abdominal radiography were ranges from 5.15 mGy to 17.86 mGy for AP and 7.33 mGy to 30.74 for lateral radio graphical examination setup. The average values were 9.43 mGy and 14.21 mGy for AP and LAT radio graphical examination respectively. The variation in the measured dose may be attributed to different imaging parameters used for different patients.

Conclusion: BARC developed OSL Dosimeter are found suitable to measure the patient dose during abdominal radiography. Further the measured doses are in line with reported dose by other researcher.

   P-173: Quality Assurance Assessment of Conventional Diagnostic X-Ray Installations in Mizoram Top

Jonathan Lalrinmawia, Kham Suan Pau 1, Ramesh Chandra Tiwari

Department of Physics, Mizoram University, 1Department of Oncology, Mizoram State Cancer Institute, Aizawl, Mizoram, India. E-mail: [email protected]

Introduction: The main purpose of Quality Assurance (QA) is to have finest X-ray image with lowest dose delivered to the patient and to reduce the rejection of poor images. In Mizoram there were 195 X-ray facilities installed in 118 different institutions till June 2016. However, in the present study, we considered 135 conventional X-rays because 90.94% workload of all diagnostic procedure in the present study area comes under these equipment [Figure 1]. Among 135 equipment 24 were condemned and the average age of the 111 equipments was 7.95±7.51 years. To the best of authors' knowledge, no proper QA assessment had been done so far in the present study area.
Figure 1: The locations of 135 conventional diagnostic X-rays installed in 82 institutions

Click here to view

Materials and Methods: To measure output radiation dose, a battery operated portable dosimeter RAD-CHECKTMPLUS (FLUKE-USA), was used. The calibration measurements were traceable to National Institute of Standard and Technology. By an internal ionization chamber, X-ray was measured in Roentgens and it can measure from 0.001 R-1.999 R. The portable digital kVp meter (FLUKE-USA) was used to measure noninvasively the effective peak potential. Others safety parameter, frequency of QA, type of Patient entrance Door (PED), availability of Personnel Monitoring Service (PMS) etc. was studied. Data presented as mean ± standard deviation (SD) were analyzed in SPSS version 17.

Results and Discussion: Coefficient of Linearity (CL) of time ranged from 0.00 to 0.93 with mean 0.20±0.19SD, 59.18% units were having CL above 0.1 (n=98). CL of current varied from 0.00 to 0.97 with mean 0.25±0.18SD, 82.61% were having CL above 0.1 (n=69). Coefficient of Variation (CV) for tube output reproducibility ranged from 0.00 to 0.72 with mean 0.08±0.12SD. Among them 35.05% were having CV above 0.05 (n=97). Tube output (70kV, FDD=100 cm) ranged from 1.57 to 236.82 μGy/mAs with mean 31.00±33.63SD. While, 7.22% were having table dose between 43-52 μGy/mAs, 25.77% were having 26-43 or 52-69 μGy/mAs and 67.01% were having dose <26 or >69 μGy/mAs (n=97). Voltage accuracy ranged between -0.32 to 0.88 with mean -0.16±0.20 SD. Among them 10.30% units come under ±5%, 10.30% units under ±10% and the rest 79.38% were above ±10%(n=97). It was found that more than half of the units were having problem in X-ray generators, voltage accuracy and table dose. Improper quality control, old equipments and lack of awareness among radiation workers may be the main reason. In other safety parameter, 39.8% X-ray rooms were not sufficient; 97.96% equipments were not facing QA test after installation; 6.12% installations were without PED and 82.65% were using non-lead-line PED; 33.67% installations were not having barrier however 25.51% were using barrier without lead-glass; 3.06% institutions were having waiting area inside the room and 20.41% near PED; chest stand of 10.20% were placed near window and 12.24% put near PED; 86.73% were not having warning light; only 8.16% used PMS; 93.88% repeated exposure occasionally due to patient movements/over/under exposed; 21.88% collimator bulbs were not working; 10.20% equipment were not having operator; 1.02% X-ray workers were not qualified (n=98) and all data presented in [Table 1]. It shows that most of the institutions were not following national and international recommendation [Table 1].
Table 1: Different important safety parameters

Click here to view

   P-174: 3D Imaging Performance Characterization in Prototype Breast Tomosynthesis Top

Seungyeon Choi1, Sunghoon Choi2, Haenghwa Lee2, Donghoon Lee1, Dohyeon Kim1, Young-Wook Choi3, Hee-Joung Kim1,2

Departments of 1Radiation Convergence Engineering and 2Radiological Science, Yonsei University, Wonju, 3Korea Electrotechnology Research Institute, Ansan, Korea. E-mail: [email protected]

Introduction: In recent years, digital breast tomosynthesis (DBT) has been developed and investigated in clinical practice because it provides a three-dimensional (3D) information of internal structures with much lower dose compared to computed tomography (CT) using relatively simple hardware. Similar to CT, the reconstructed image quality from DBT depends on the variety of parameters during reconstruction process. To achieve the best clinical outcome, it is crucial to understand the fundamental imaging characteristics. The spatial resolution and noise are the standard image quality metrics for assessment in both 2D radiography and 3D tomographic images.

Objectives: The authors observed 3D imaging performance in a prototype DBT system using two different reconstruction algorithms: a filtered back-projection (FBP) and ordered subset expectation maximization (OSEM). The main focus of the current work is not to rate the superiority of two algorithms, but mainly focused on comparison of imaging characteristics which depend on imaging conditions.

Materials and Methods: In this study, we used the prototype DBT system developed by Korea Electrotechnology Research Institute for breast imaging research, which is currently under evaluation for clinical application. The system is based on a flat-panel-detector (2923MAM, Dexela Ltd., UK) with a pixel size of 0.075×0.075 mm2. The system acquired a total of 11 projection images while moving over a total angular range of ±9° with angular spacing of 2.5°. The detector was stationary during tomosynthesis acquisition. The FBP and OSEM reconstruction algorithms were implemented using total 11 projection views. Iteration numbers for OSEM were varied with 8, 12 and 16 and the number of subsets was set to 3 during whole reconstructions. Spatial resolution and noise of the system were quantified based on in-plane modulation transfer function (MTF), in-plane noise power spectrum (NPS), and voxel variance. For MTF measurement, a slanted edge of a 0.8-mm thick stainless steel plate was placed on 2 cm above the center of the detector surface near the chest wall side. The ensemble averaged 1D edge spread function (ESF) over the same reconstructed in-planes of 20 repeated acquisitions was calculated. On the other hand, in-plane NPS was calculated as a quantum noise of a volume-of-interest in the scanned breast phantom, removing mean signals of 20 repeated tomosynthesis images from original image. In-plane NPS was calculated by taking Fourier transform of the ensemble averaged mean subtracted sub-images in a targeted in-plane.

Results and Discussion: The spatial frequencies at which the in-plane MTF reduced to 50% were 0.86, 0.93, 0.93, and 0.94 cycles/mm for FBP, and OSEM with iteration number of of 8, 12, and 16, respectively and data presented in [Figure 1]. The FBP provided inferior resolution than OSEM with iteration number of 8, 12 and 16. The in-plane NPS for FBP and OSEM showed exactly symmetrical patterns followed by the central slice theorem, however, FBP presented more anisotropic .shape compared to OSEM as shown in [Figure 2]. Voxel variance that was measured by integrating the whole 3D NPS was proportional to the number of iterations in the OSEM, giving 0.89× 106, 1.67× 106, and 2.54× 106 for iteration number of 8, 12, and 16, respectively. The FBP data was 1.42× 106, which was in the middle of the data from 8 and 12 iterations of the OSEM.
Figure 1: The in-plane modulation transfer function for filtered back-projection and ordered subset expectation maximization with iteration number of 8. The modulation transfer function data for ordered subset expectation maximization with iteration number of 12 and 16 were similar to that from 8 iteration

Click here to view
Figure 2: The normalized in-plane noise power spectrum for (a) filtered back-projection, (b) ordered subset expectation maximization with iteration number of 8, (c) 12, and (d) 16

Click here to view

Conclusion: A comparative study between FBP and OSEM reconstruction schemes would provide the quantitative imaging characteristics in the DBT system.

   P-175: Comparative Performance Analysis for Lungman Phantom Simulated Tumors Detectability According to Computed Tomography Reconstruction Algorithm: Focused on Advanced Modeled Interative Reconstruction Algorithm Top

Jun-Bong Shin, Do-kun Yoon, Tae Suk Suh, eong-Yong Pak1, Yang-Ho Kwon1

Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, 1Siemens Healthcare,Seoul, Republic of Korea. E-mail: [email protected]

Introduction: As a development of a computed tomography (CT) device progresses, reconstruction techniques of the CT have been advanced simultaneously. In addition, a requirement of new CT reconstructions has been improved for a clinical field. Thus, we analyzed the difference of the performance CT images depending on the type of CT reconstruction.

Objectives: We compared and analyzed the detectability performance regarding a LUNGMAN phantom including simulated tumors according to CT reconstruction algorithm.

Materials and Methods: In this study, three kinds of the reconstruction algorithm (filtered back projection; FBP, sinogran affirmed interative reconstruction; SAFIRE, advanced modeled interative reconstruction; ADMIRE) were used to deduce the detectability performance. In order to compare and analyze contrast to noise rate (CNR), coefficient of variation (COV) of the LUNGMAN phantom simulated tumors (15 variations 3 varietles of Hounsfield numbers: -800, -630, +100, 5 sizes for each time: diameter 3, 5, 8, 10, 12 mm), SOMATOM Definition Flash CT device were fixed at field of view (FOV) of 300 mm size, slice thickness of 3.0 mm/increment 3.0 mm, and reconstruction kernel I40f medium, and investigated for 10 repeated times with eight radiation energy conditions (120/100 kVp, 60/80/100/120 mAs).

Results and Discussion: Depending on three kinds of reconstruction algorithm (FBP, SAFIRE, ADMIRE), we will compare the images of the LUNGMAN phantom simulated tumors (15 variations 3 varietles of Hounsfield numbers: -800, -630, +100, 5 sizes for each time: diameter 3, 5, 8, 10, 12 mm). Then, you will find the mode of the algorithm suitable for the evaluation of the phantom images. Our study would suggest that the best CNR and the COV were high among three kinds of reconstruction algorithm.

   P-176: CT Number Accuracy of Metal Artifact Reduction Algorithm and its Influence on Radiaotherapy Treatment Plannng Top

Vishram Naik, R. Holla, B. Pillai

Department of Medical Physics and Radiation Safety, Amrita Institute of Medical Sciences, Amrita Vishwa Vidyapeetham, Amrita University, Kochi, Kerala, India. E-mail: ???

Introduction: Artifacts can seriously degrade the quality of CT images which can make the images diagnostically unusable. To optimize image quality, it is necessary to understand why artifacts occur and how they can be suppressed. In following studies two metal artifact reduction algorithms SMAR (Smart Metal Artifacts Reduction) on GE optima 580W and OMAR (Orthopedic –Metal Artifact Reduction) on Philips ICT 256 are used.

Objectives: HU consistency is challenging when metal artifact reduction algorithm is used in radiotherapy treatment planning.

Materials and Methods: CT numbers were measured before and after applying the metal artifact reduction algorithm on both CT machine GE optima 580W and Philips ICT 256. We used Gammex 467 (Middleton, WI 53562, USA) tissue characterization having different tissue rods. The phantom was scanned with 80, 100.120, & 140 kV and FOV 50 cm. All reconstructed images were 12-bit depth images. The data was analyzed and HU error, diameter error of titanium and stainless steel and relative error was found.

Results and Discussion: Evaluation of CT number accuracy by two metal artifact reduction algorithms was studied. One is on GE optima 580W the algorithm is known as Smart Metal Artifacts Reduction (SMAR) and second is Philips ICT 256 the algorithm is known as Orthopedic –Metal Artifact Reduction (OMAR). Both showed good results in reducing metal artifact streaks and CT number accuracy at energy 140kV which error in HU was < 20 HU.

We studied metal detection technique an algorithm used to reduce metal artifacts on Siemens Somatom Evolution which is known as Extended CT Scale (ECTS) which extend the CT number -1024+3071 to -10240 +30710. We used titanium and stainless steel in study were we found that CT number increased from +3071 to +13650.65 HU at 80kV, +12250.55 HU at 100kV and +12076.34 HU at 130 kV for stainless steel and for titanium increased from +3071 to +9383.8 HU at 80kV, +7367.86 HU at 100kV and +6411.7 HU at 130 kV. It was observed that after applying ECTS as energy increases the HU number of metal was decreased. For rest all tissue equivalent plugs, HU were unchanged by applying ECTS technique. We also studied the metal diameter accuracy for a physical diameter of 13 mm for titanium and stainless steel. The metal diameters were measured on scan images from lower to higher energy. It was observed that diameter error was more for less energy. For 140kV diameter error after applying SMAR was 1.63 mm for titanium and 2.63 mm for stainless steel. For 140kV diameter error after applying OMAR was 1.65 mm for titanium and 2.97 mm for stainless steel.

   P-177: Effects of Slice Thickness for Prototype Digital Breast Tomosynthesis Top

Haenghwa Lee1, Sunghoon Choi1, Hyemi Kim1, Donghoon Lee2, Dohyeon Kim2, Chao Zhen2, Seungyeon Choi2, and Hee-Joung Kim1,2

Departments of 1Radiological Science and 2Radiation Convergence Engineering, Research Institute of Health Science, Yonsei University, Wonju, Korea. E-mail: [email protected]

Digital breast tomosynthesis (DBT) is an emerging 3D imaging technology that can improve the detection of breast cancer by preventing tissue overlap. There are many parameters that must be decided to achieve maximum performance in DBT system, and one of these parameters is the slice thickness. The purpose of this study was to evaluate the effects of slice thickness on the detection of micro-calcification for prototype DBT system. A prototype DBT system (Korea Electrotechnology Research Institute) consisted of an X-ray tube (XM1016T, Industria Applicazioni Elettroniche, Italy) and a CsI (Tl) scintillator/CMOS flat panel digital detector (2923MAM, Dexela Ltd., UK) with a matrix size of 3072 x 3888. The CIRS phantom (Models 014 series, USA) was included micro-calcifications with nominal specks size of 0.20 mm, 0.23 mm, 0.27 mm, and 0.39 mm. When we acquired the 15 projection views with a 42 angular range, average glandular dose (AGD) was about 1.08 mGy. The projection views were reconstructed using filtered back-projection (FBP) method, and a total of six different average slice thickness were used. We evaluated the quality of reconstructed images with contrast-to-noise ratio (CNR), artifact spread function (ASF), and quality factor (QF). We found that detection performance of calcification size was influenced by slice thickness in DBT system. Although CNR values raised to a peak when slice thickness was similar in size to the calcification to be detected, ASF curves for all calcifications improved with decreasing slice thickness. QF factors were more affected by CNR than ASF curves. These results showed that thinner slice thickness could improve detection of small lesions. In conclusion, optimal slice thickness of different calcification size could provide more satisfactory image for the detection of lesions using DBT system. Although proper slice thickness could yielded superior image quality, further studied are needed to evaluate the effect of slice thickness considering reconstruction speed.

Acknowledgment: This research was financially supported by the Ministry of Trade, Industry and Energy (MOTIE), Korea Institute for Advancement of Technology (KIAT) and Gangwon Insititute for Regional Program Evaluation (GWIRPE) through the Economic and Regional Cooperation Industry.

   P-178: New Protocol to Reduce Fetal Radiation Dose During Prophylactic Balloon Insertion in Pregnant Patients with Abnormal Placental Adherence Top

H. Al-Naemi, N. Iqeillan, A. Aly, A. Omar1, A. Barah1, A. Abualruz1, M. B. Gomaa1, A. Almuzrakchi1, V. Chavan1, O. AlMokdad1

Departments of Occupational Health and Safety and 1Clinical Imaging, Hamad Medical Corporation, Qatar. E-mail: [email protected]

Background: Abnormal Placental Adhesion (APA) is a life-threatening condition which occurs in approximately one in 2,500 deliveries,[1] it is divided into three grades based on histopathology: placenta accreta, placenta increta, and placenta percreta.[2] More than 50% of APA patients recieved blood transfusion or admitted to an ICU and the mortality rate is greater than or equal to 7%. [3,4] Moreover, placenta accreta is the leading cause of peripartum hysterectomy,[5] Prophylactic Iliac Balloon Insertion (PIBI) is introduce as an adjuvant therapy in order to minimize blood loss during cesarean or in conduct with conservative management with the intent of avoiding hysterectomy in selective cases.[6]

Objective: The purpose of the present study is to evaluate a new protocol aimed to minimize the fetal radiation exposure during PIBI in patients with high risk of morbidity due to APA and to assess its effect on technical success during the angiography.


  • Retrospective study comparing 2 groups of pregnant patients with APA eligible for PIBI.
  • Control group: 11 patients underwent standard protocol of radiation dose reduction.
  • Study group: 11 patients underwent new protocol of radiation dose reduction.
  • Peak Skin Dose (PSD) and Fetal Absorbed Dose (FAD) were calculated indirectly from the peak Entrance Skin Air Kerma (ESAK).
  • Radiation parameters measurements of the two groups were collected, compared and further compared to international standards.
  • At the end of each PIBI, the difficulty of the procedure using new protocol was estimated based on the quality of fluoroscopy images and arterial anatomy.
  • Used standard dose reduction parameters.

Results: Because of wide range of FAD and PSD in group 1, Mann-Whitney test has been used for p value calculation. The mean value of FDA was 21.92 +/- 19.1 in control group and was 1.5 +/-1.27 in study group (p = 0.0001). The mean value of PSD was 93.54 +/- 80.8 in control group andwas 6.29 +/- 5.39 in study group (p = 0.0001) as shown in [Table 1] and [Figure 1]. There was no significant difference in mean fluoroscopy time between the two groups (1.88 +/- 0.66 vs 2.51 +/- 1.30, p = 0.167).
Table 1: Peak skin dose, fetal absorbed dose, fluoroscopy time and P value for study

Click here to view
Figure 1: Mean values of fetal absorbed dose and peak skin dose for control group and study groups

Click here to view

Discussion: Particular attention must be paid to dose reduction techniques in order to minimize the radiation exposure to the fetus during X-ray-based procedures. In our study, the median FAD from PIBI was reduced from 22 to 4.7 mGy by implementing the new protocol which decreases the stochastic effect. Compared to standard practice of PIBI, the main parameters that decreases the FAD during PIBI was the use of low dose protocol and the retrieval of the grid before the procedure. Operator experience may also influence FAD on PIBI procedures. In fact, experienced operators perform the procedure with confidence that they can achieve an appropriate compromise between the lower image quality due to the new protocol whilst achieving technical success as shown in [Figure 2].
Figure 2: Fluoroscopy image showing the inflated balloon catheter in the right internal iliac artery using the standard protocol (a) and the new protocol (b), respectively

Click here to view

Conclusion: It has been demonstrated by the present study that the application of new protocol for radiation dose reduction significantly reduces the FAD and PSD during PIBI in pregnant patients with APA. This new protocol can easily be applied and does not affect the technical success of the angiography procedure.

   P-179: Implementation of Three Dimensional Micro CT Image Reconstruction on Graphics Processing Unit Top

Kamirul, L. A. Fitri, F. Haryanto

Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Bandung, Indonesia. E-mail: [email protected]

A GPU-based (Graphics Processing Unit) program has been developed to perform reconstruction process on micro CT scanner projection images. The program was implemented using FDK (Feldkamp, Davis, and Kress) which is intended to reconstruct three dimensional volume from projection images acquired using conebeam X-ray with a planar detector configuration. Based on simulation performed on GTX 780 GPU (2304 cores), the program was able to accelerate filtered-backprojection process up to 89,90 times compared to Intel CoreTM i5-4330 CPU (Central Processing Unit) implementation on 20483 voxels phantom. By varying voxels number, it can be shown that acceleration values were influenced by the number of reconstructed voxels and available global memory size on GPU. Maximum total acceleration value was 27,93 obtained when 10243-voxel phantom was reconstructed on 2,05 GB GPU memory. Further result show that developed program was capable of producing acceleration values to 1.27 and 1.30 compared to NRecon software on medium (11203 voxels) and high (22403 voxels) resolution aquades phantom. While in low-resolution (5603 voxels), the program yields a de-acceleration value of 0.85.

   P-180: Estimation of Radiation Doses in Diagnostic and Interventional Theraputic Radiological Procedures Top

Bhupendra Singh Rana, Amitabh Sinha, Sanjeev Kumar1, Naveen Kalra, N. Khandelwal

Department of Radiodiagnosis and Imaging, PGIMER, 1Department of Physics, SD College, Chandigarh, India. E-mail: [email protected]

Introduction: Interventional radiology (IR) is an important imaging modality for early detection and treatment of complex diseases, with advantages such as non-invasiveness, timeliness, reliability, and minimum pain to the patient.[1] However, these procedures result in significant radiation doses to the individuals undergoing imaging and therapeutic procedures as well as to the operators of the procedures. The high radiation doses delivered during IR procedures are associated with higher stochastic risk as well as higher chances of manifestation of deterministic injury to the patients, if a threshold dose to these deterministic effects is exceeded.[2] Skin tissue most likely to get maximum dose during IR procedures. There has been concern to minimize doses to some critical organs during interventional radiology. These concerns require modifications of work practices as well as optimization of procedures. However, the magnitude of dose delivered to the patients depends on many radiographic factors viz., use fluoroscopy on time, mA, tube voltage, radiosensitivity of the organ, complexity of the procedure, experience of the operator and patient specific parameters. Various authorities such as International Commission on Radiological Protection (ICRP)[3] and International Atomic Energy Agency (IAEA)[4] have expressed concern over patients' skin dose during interventional radiology procedures. In the present study, we measured the entrance surface dose (ESD) for various diagnostic and therapeutic interventional procedures.

Objectives: The aim of the work is to measure and analysis of skin entrance doses (SEDs) for various diagnostic and therapeutic interventional radiological procedures.

Materials and Methods: IR procedures were classified according to the type of examination outcome in two categories known as diagnostic IR and therapeutic IR. In present work we estimated the radiation exposures to the patients in six diagnostic (Cerebral angiography, abdomen angiography, IVC graphy, lower limb angiography/venography, upper limb angiography/venography and Spinal artery angiography) and six therapeutic (Abdominal procedures, angioplasty, AVM embolization, bronchial artery embolization, intra artery thrombolysis, renal artery embolization) interventional procedures from the registered dose area product (DAP). The measurements are part of quality assurance study comprised data recorded from all patients undergoing procedures in the interventional radiology section of PGIMER, Chandigarh. Data was gathered on 300 patients, patient age, sex, DAP reading, fluoroscopy time and type of procedure were recorded. All fluoroscopy and imaging were performed on Allura Xper FD 20/10 angiographic unit (M/s Phillips Medical systems, Germany). It is ensure that angiographic unit used in study met the quality assurance (QA) criterion for KVp, mAs, current, time, field size, filtration and radiation output as specified by Atomic Energy Regulatory Board (AERB), Mumbai. The initial evaluation independently verified the unit's entrance skin exposure calibration by measuring the beam output using 75 cc shadow free Ionization chamber and UnidosE dosimeter (PTW, Freiburg, Germany) and compared the measured output with the DAP readings shown on the units control console measured by inbuilt ionization chamber in the collimator of the machine.

Result and Discussion: It is clear from experimental results, in case of interventional radiological procedures patients undergone spinal artery angiography received maximum radiation exposure and minimum exposure in case upper limb angiography/venography procedure. On the other hand in case of therapeutic radiological procedures, patients received maximum exposure in abdominal and minimum exposure in intra artery thrombolysis. The present study shows that patients received doses that varied considerably during x-ray-based interventional imaging.

Hricak H, Brenner DJ, Adelstein SJ, Frush DP, Hall EJ, Howell RW, et al. Managing radiation use in medical imaging: A multifaceted challenge. Radiology 2011;258:889-905.

Klein LW, Miller DL, Balter S, Laskey W, Haines D, Norbash A, et al. Occupational health hazards in the interventional laboratory: Time for a safer environment. Catheter Cardiovasc Interv 2009;73:432-8.

Valentin J. Avoidance of radiation injuries from medical interventional procedures. Ann ICRP 2000;30:7-67.

International Atomic Energy Agency. IAEA-TECDOC-1641. IAEA; 2010.

   P-181: General Methods Of 2D, 3D and Deformable Image Registration Top

Bhumika Handa, Gaganpreet Singh, Rose Kamal, Arun S. Oinam1, Vivek Kumar

Centre of Medical Physics, Panjab University, 1Department of Radiation Therapy, Regional Cancer Centre, PGIMER, Chandigarh, India. E-mail: [email protected]

Introduction: Image registration methods are of great interest these days due to the advancement in radiotherapy treatment techniques. Image registration includes various steps such as image segmentation, image fusion and post processing techniques. Many methods have been developed for 2d-2d, 3d-3d and deformable image registration techniques incorporating complex statistical and mathematical models.

Objective: Review of various image registration methods and development of image registration tool for various imaging modalities like CT, MRI to obtain complete information about the morphological changes inside the patient.

Materials and Methods: In this study Different image data sets of CT AND MRI are used. Indigenous image Registration tool is developed in MATLAB Software, which provides image registration of two or more data sets. 2-D image registration was performed using various methods like point Based Registration, Gradient Correlation and Principal Component Analysis. For 3-D image Registration various methods used are Principal Component Analysis, Iterative Closest point, Wavelet based, B spline based, and SVR (Special vector regression) based method. Extended version of these methods issued in deformable image registration.

Result and Discussion: To analyze the accuracy and uncertainty associated with the image registration techniques, various statistical parameters like mean Standard Deviation, Variance, Correlation, Entropy, Root Mean Square error and Chi Square test are used. Point based image registration is an error prone method because of the user inputsand intensity based method gives accurate result only in same modality images and difficult to use in different modalities. Various complex methods such as SVR, PCA, ICP have their advantages as well as limitations in different scenarios.

Conclusion: The 2d-2d and 3d-3d image registration methods include complex athematical formulism, which are still in growing stage. Although many methods have been developed, in present work it is found that every method has its own limitations. In this study various methods for planar and volumetric data has been used. This study can be further extended to built a generalized method for 2d, 3d and deformable registration.

   P-182: Standard Procedures for Estimating the Uterine Dose During Fluoroscopy Examination Top

K. Schröder, Kilian Seth, K. Loot, A. Block1

TU Dortmund University, 1Institute for Medical Physics, Klinikum Dortmund GmbH, Dortmund, Germany. E-mail: [email protected]

Introduction: The exposure of ionizing radiation on embryos during a medical indication can cause severe physical and mental disabilities. There are a couple concepts for theoretical determinations of the applied dose which can then be used to carry out a risk assessment of the radiation induced damage. Examples of these concepts are provided by the DGMP report No.7 of 2002. The Dose calculations in this report are based on a Three-Step-method. If the estimated dose of step one exceeds a threshold value, further calculations must be carried using concepts like the image receiver- or the source concept. In this work, the image receiver concept is used to compare reference-dose values from 15 years ago with recently measured ones to find out if they can be reduced.

For this, theoretical dose calculations as well as continuous and pulsed phantom measurements are carried out on three C-arms of various technical generations.

Objectives: The reference-dose values assumed at the time of the report are conservative. In order to estimate how conservative they are, theoretical calculations of the dosage were carried out with the Image receiver concept. That uses the formula:

with the incident dose KE, a scaling between skin and uterus depth, the Mass absorption coefficient twa and the tissue to air ratio Ta, to calculate the Uterus dose. The incident dose is the product of attenuation coefficients, the fluoroscopy time and the image receiver performance. It turns out that the reference-dose values from the report include a safety buffer of around 40% to take the worst conditions into account.

Materials and Methods: After the theoretically determined doses, experimental measurements are carried out, in which the conditions are reproduced from the report with a water equivalent phantom. The measured and calculated values for the uterine dose are significantly smaller than the reference values. The measured values are between 45 and 93% smaller than the reference-dose values. It could be expected that a reason for the deviating doses from the reference values is, that the devices used at the time of the report cause a higher dose load than devices of today's development level. However, during continuous fluoroscopy, this assumption is rejected, since the reference values take account of the individual image receiver performance. Yet there are tremendous differences between the dose rate of the newer and the older C-arm.

Results: The decisive factor is that a continuous fluoroscopy at the new C-arm is not possible and that the measurements have been approximated with a high pulsation. In 2002 most of the C-arms only had the function of continuous fluoroscopy. However, nowadays pulsed fluoroscopy achieves considerable dose reduction, which the report does not consider. That is why the phantom measurements are repeated under the same conditions, with the difference that pulsed fluoroscopy is applied. The radiation load for the embryo with pulsed fluoroscopy is significantly lower than with continuous. This, in turn, corresponds to a reduction of the reference dose values from the report of 59-92%. For innovative reference dose values consideration should be given to pulsed fluoroscopy.

Discussion: The results of this study show that concepts for dose calculations like the image receiver concept are still accurate. Yet, it is advisable to extend reference dose values with different pulse frequencies, since there are devices that does not have the option of pulsed fluoroscopy anymore. For those the reference values are invalid.

   P-183: Cone Beam Computed Tomography Image Quality and Dose Optimization Top

Gaurav Trivedi1,2, C. K. Dixit2, Arun Oinam1, Ranjit Singh1, Ngangom Robert1, Amanjot Kaur1

1Department of Radiotherapy & Oncology PGIMER, Postgraduate Institute of Medical Education and Research, Chandigarh, 2Department of Physics, Dr. Shakuntala Misra National Rehabilitation University, Lucknow, Uttar Pradesh, India. E-mail: [email protected]

Imaging is prerequisite for positional setup correction of the patient before radiation dose delivery. Imaging can either be obtained by MV source detector system or by the help of kV source detector system. Three dimensional Cone beam computed tomography imaging is possible using latter mode of imaging. CBCT imaging delivers lesser dose to the patient compare to MV imaging. But as the unnecessary radiation exposure to any part of the body other than target site can become potential site for secondary malignancy. The dose due to CBCT imaging needs to monitor. The aim of this study was to estimate and optimize the doses due to kV CBCT imaging of Head & neck and pelvis region of the patient. The study was done to evaluate the effect of different filters on patient doses without much affecting the image quality. Imaging Dose to the patient was estimated using CTDI phantom. Both H&N as well as Pelvic CTDI Phantom were used to measure Cone Beam Dose Index (CBDI). A system for imaging the Patient on treatment couch using kV source (G242) and flat pannal detector system (PaxScan4030CB) added on Trilogy linear accelerator by varian medical system, Inc, Palo Alto, California was used. This system known as On Board Imager (OBI) has an active area of 397 mmX298 mm and it is capable to provide good quality 2D radiograph and 3D Cone Beam Computed tomography (CBCT) image. For pelvis, single protocol of 125kV-80mA was used with half bow tie filter whereas for H & N region three protocols of High quality head (100kV-80mA), low dose head (100kV-10mA) and standard dose head (100kV-20mA) were used with full bow tie filters. The dose delivered in a CBCT procedure was assessed using a cylindrical Perspex phantom (diameter, 32 cm body phantom and 16 cm Head and Neck phantom) with a calibrated Farmer type cylindrical ionization chamber (10 cm active length) in conjunction with a DOSIMAX plus A, iba dosimetry, Germany electrometer. Maximum Dose reduction of 7.1 % was observed in Pelvis protocol with additional brass alloy filter. The maximum dose reduction was observed in High quality head protocol and that was 25% for the same brass filter. Different factors to define image quality likes special resolution, contrast to noise ratio and uniformity was assessed on CATPHAN-500 with the no of filters to monitor the stability of the imaging quality. Acceptable image quality was observed with the brass and copper filters with reduced imaging dose.

   P-184: Scattering, Absorption and Extinction Characteristics of Electromagnetic Wave by a Spherical Particle Top

S. M. Kurawa, M. M. Kashimbila1

Sa'adatu Rimi College of Education, Kumbotso, 1Bayero University Kano, Kano, Nigeria. E-mail: [email protected]

The scattering of electromagnetic wave by a spherical particle was presented using the Mie formulation. The parameters needed to describe the characteristics of the radiation scattered by the particles were derived. The parameters include the Mie coefficient an and bn, the scattering, absorption and extinction efficiencies, the cross section for radiation pressure and the asymmetry factor <cosθ>. The behavior of these parameters was investigated as functions of the dimensionless size of the particle (2πr/λ). Experimental value was obtained from radiation pressure measurements on a levitated oil droplet with refractive index of m= 1.29. It was found that the various efficiency factors are related to the optical property of the scattering. For pure dielectric, the efficiency factors for scattering and extinction are equal, since there was no absorption. Superimposed on the extinction curves are the minor oscillations called ripple structures. When the particles were absorbing, the refractive index became complex, it was found that the amplitude of the extinction curve decreased, and the ripple structures gradually disappeared. Similarly, the distance between resonances, also called the period of resonances was found to be related to the refractive index of the particle. Using the Mie theory, the period calculated was 0.750, which was in good agreement with the experimentally quoted value of 0.671.

   P-185: Dosimetric Comparison Between Nomex Multimeter and Rad Cal Ion Chamber in Nucletron Simulix Evaluation Simulator Top

C. Senthamil Selvan, C. S. Sureka, Raghavendra Holla1

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, 1Department of Medical Physics and Radiation Safety, Amrita Institute of Medical Sciences and Research, Kochi, Kerala, India. E-mail: [email protected]

Introduction: X-ray tube performance is considered as one of the most important issues in medical imaging science and radiation protection. Hence, all necessary measures should be taken to maintain an effective performance of the X-ray machine through regular calibration and maintenance. Based on this, quality assurance tests of diagnostic x-ray tube are carried out periodically because poor performance of the equipment will directly lead to poor image quality and increase the dose to the patients. Therefore, the selection of an appropriate instrument for dosimetry should be done very carefully.

Objectives: The objective of this study is to evaluate the X-ray tube voltage (kVp), current (mA), exposure time (milliseconds), half value layer (HVL), leakage radiation and compare the radiation output in Nucletron Simulix Evolution using semiconductor based NOMEX multimeter (D-1) and ion chamber based detector Rad Cal 9095 (D-2).

Materials and Methods: This measurement includes 50 selected parameters with stranded experimental setup includes gantry, collimator and couch rotation angle at 00, and the focus to couch distance was 100 cm. Both the detectors were placed very close to the isocentric point and the collimator opened for 30×30 cm2,. The operating parameters were varied from 60 kVp to 120 kVp at 10 kVp interval at 50 mA, 100 mA and 200 mA with respect to different exposure time in the range of milliseconds for the measurements of kVp, mA and exposure time. The HVL measurement was performed with added aluminium filters at the operating parameter of 120 kVp, 100 mA and1000 mSec. The leakage radiation was measured using the pressurized μR ion chamber survey meter (451P-RYR) at 1 meter distance from the X-ray tube focus to with the set parameters of 130 kVp, 100 mA and 1000 mSec.

Results and Discussion: The measured kVp in D-1 and D-2 values were compared, the maximum kVp error from ±2.2 kVp to ±11.1 kVp and the practical peak voltage (PPV) is 0 to ±11.3 kVp and mean kVp errors is ±0.2 kVp to ±11.6 kVp. The measured exposure time varied in D-1 is 0 to 4.5 msec and D-2 is 0 to 1 msec. The measure HVL values were within the acceptable limit as per the AERB guidelines. In output measurements, more deviation observed in D-2, the values from 18.78 mR to 588 mR compared to D-1. The maximum leakage radiation is 1.68 mR/hrs. From this data, it is observed that the semiconductor based detector D-1 gives more reliable data than ion chamber based detector D-2 for all the selected parameters and for output measurement.

   P-186: CT Doses Estimation with the Dosimetric Quantities CTDI and Dap to Define Diagnostic Reference Levels in Interventional Radiology Top

Jyoti Bisht, S. P. Mishra, Sonal Vashnerya1, Raj Kumar Tyagi2

Department of Radiation Oncology, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, 1Department of Radiotherapy, All India Institute of Medical Sciences, Jodhpur, Rajasthan, 2Government Post-Graduation College, Kotdwar, Uttarakhand, India. E-mail: [email protected]

Introduction: CT simulation provides a graphic display of the 3D anatomy of both normal tissue and cancerous tissue and it is capable of interactive three-dimensional (3D) volumetric treatment planning this allows radiation oncology departments to operate without conventional x-ray simulators. Current computed tomographic (CT) scanners generate patient dose indexes of the volume CT dose index (CTDIvol) and the dose length product (DLP).

Method: CTDIvol is an index that quantifies the relative intensity of the radiation that is incident on the patient. CT scanners that have patient size– specific scanning protocols would likely select lower CTDIvol values for pediatric patients but higher ones for oversized patients. The total amount of radiation delivered to the patient at a given examination, however, is also dependent on the CT scan length. The product of CTDIvol and scan length is the DLP, which can be used to quantify the total amount of radiation patients receive during a given scan. The DLP is directly related to the patient (stochastic) risk and may be used to set reference values for a given type of CT examination to help ensure patient doses at CT are as low as reasonably achievable. In CT examinations, the CT dose index (CTDI), the Dose Length Product (DLP) and the effective dose are the most common used dosimetric quantities for DRLs.

Discussion: In comparison to conventional radiography, CT is a high-dose imaging modality, although doses are generally well below the threshold dose for the induction of deterministic effects. CT imaging is now the dominant contributor to the population dose from medical x-rays, where the latter is the major source of radiation exposure from man-made sources. Results of one study estimated that although CT accounted for only 10% of diagnostic examinations in US hospitals in 2000, this imaging modality accounted for nearly 70% of the corresponding medical dose. Because the CTDI is an averaged dose to a homogeneous cylindrical phantom, the measurements are only an approximation of patient dose. Another limitation is that CTDI overestimates dose for scans where the patient table is not incremented, such as in interventional and perfusion CT. For these CT applications, the CTDI can overestimate peak dose by a factor of two.

Conclusion: Several actions are to be undertaken to limit the irradiation of patients: lowering the high voltage (kV) and the tube current (mAs), reducing the scanning length and the tube rotation time, increasing slice thickness or pitch, using auto-exposure control or dose reduction software, and the training of staff. Regular awareness of medical imaging professional on radiation protection during staff, meetings and national and international meetings/workshops would also disseminate best practice and harmonize the best CT-scan protocols. There is also need for quality control of CT Equipment and audit of CT practices to alert professional in case of inappropriate practice.

   P-187: Radiation Leakage Test for Lead Aprons Our Experience Top

R. Pichumani

Jawaharlal Nehru Hospital & Research Centre, Bhilai Steel Plant, Bhilai, Chhattisgarh, India. E-mail: [email protected]

Introduction: Lead aprons are used in various departments of our hospital. We have a routine test for lead aprons at our Institute for cracks using fluoroscopic procedures once in 6-8 months.

Materials and Methods: This poster describes our experiences with the lead aprons and testing of lead aprons (with images). This poster demonstrates the importance of lead apron testing using fluoroscopic procedures. On an average of 50-60 lead aprons are tested every time. The poster also describes the importance of testing the lead aprons before accepting it for regular usage.

Results and Discussion: It is very important to have leakage test for lead aprons atleast once a year if it is regularly used and also before accepting it for use. This ensures radiation safety to radiation workers.

   P-188: Modern Imaging in Oncology: Present Challenges And Future Expectations Top

Deboleena Mukherjee, Kirti Tyagi, Partha Brata Mukherjee1, Arti Sarin2

Radiation Oncology Centre, INHS Asvini, 1Nuclear Medicine and PET/CT Centre, INHS Asvini, 2Department of Radiodiagnosis and Radiotherapy, INHS Asvini, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Imaging plays an important role in Oncology; presently Positron Emission Tomography (PET) has been integrated with Computed tomography (PET/CT) or Magnetic Resonance (PET/MR) imaging, for hybrid (combined) imaging. These hybrid systems are used to evaluate extent of disease, to detect occult lesions and monitor treatment response in respect of its metabolic activity and anatomical and functional details as well as its invasion into surrounding normal tissues before and after treatment with surgery, chemo or radiation therapy. In the last few years, there has been significant advances in radiation treatment planning (RTP) software of the treatment planning system (TPS) calculation algorithms and it is able to combine the biologically guided PET data or MR data and anatomic CT data with five registrations methods, Manual approach (MA), Landmark, Identity, Surface Matching, and Mutual Information (MI) for precise three dimensional (3D) computer based dose calculation. Hybrid imaging based treatment planning has an advantage over CT alone in the standardization of target volume delineation (Gross tumour volume (GTV), Clinical target volume (CTV), and Planning target volume (PTV) margins), in reduction of risk for geometric misses and in minimizing radiation dose to the non-target organs. The most commonly used PET radio tracer is18F-fluorodeoxyglucose (FDG), others like 18F-FMISO (fluoromisonidazole), 64Cu-diacetyl-bis (N4-methylthiosemicarbazone) and 64Cu-ATSM have also been used to demonstrate “hypoxia” and 18F-FLT (flouro-3-deoxythymidine) as a marker of “cellular or sub-cellular” proliferation and 11C-MET (Methionine) in brain imaging. Also, PET/MR is an exciting new modality for cardiovascular applications and recently 68Ga-DOTATAC has been used for RTP in meningioma patients. A new field of “theragnostics” has emerged where image fusion of PET or MR data with CT data shall be used to localize tumour sites more precisely, with other suitable tumour targeting agents labelled with 124 I (half life 4.2 days) as they are not taken up by inflamed and infected tissues. Present challenges are procurement of radiotracers from a cyclotron facility, high cost, and degradation of PET image quality due to photon attenuation in tissues and quantitative accuracy and optimal integration of the DICOM images obtained in the treatment position into TPS software. The use of 4D PET/CT imaging with respiratory compensation in the thorax improved the partial volume effect and accuracy of SUV (standard uptake value) measurements. However, some limitations have also been well documented like false-negative results with 18FFDG PET/CT may occur if a patient is scanned too early after completion of chemotherapy or radiation therapy, if there is recurrent disease; if malignancy is present in structures with a physiologically elevated metabolism (e.g., tonsillar carcinoma); or if the tumor is not FDG-avid. “Attenuation-correction” artifact results from erroneous overcorrection of PET emission data by software that uses CT transmission data for attenuation correction. This occurs in areas that have a high attenuation on corresponding CT images (e.g., enhancing blood vessels, metallic implants) and can be easily detected by evaluating the uncorrected emission PET data. Mis-registration artifact from involuntary activity is not as much a problem in head and neck 18FFDG PET/CT as in imaging the chest or abdomen. Adequate patient instruction and immobilization during scanning prevents artifact due to voluntary movements. These hybrid imaging systems also vary in terms of sensitivity, spatial and temporal resolution. Technological developments to increase imaging speed to match with physiological processes of tumour sites and use of other therapeutic agents for targeted imaging shall be the future expectations of these hybrid systems.

Conclusion: Thus, today in cancer therapy, these modern imaging hybrid systems is probably superior for more accurate diagnostic PET/CT & MRI and RTP CT scan in a single session for a variety of cancers with better visualization and detection of distant metastases.

   P-189: Dose Estimation in Water Equivalent Phantom Using GEANT4 Simulation Toolkit Top

Sachin Dev1,5, B. S. Rana2, Davinder Siwal3, Sanjeev Kumar4

Departments of 1Radiotherapy and 2Radiology, PGIMER, 3Department of Physics, Panjab University, 5Centre for Medical Physics, Panjab University, 4Department of Physics, GGDSD College, Chandigarh, India. E-mail: [email protected]

Introduction: In radiological examinations radiation dose calculations are essential to understand the relationship between risk and benefiets of medical examination. Radiological investigations use X-ray in kV range for which absorbed dose measurement in phantom is somewhat difficult process as all the energy is deposited on surface. With the help of computer simulation, various physical process can be modeled and used for absorbed dose calculation. A versatile Monte Carlo based ; Geant4 (Geometry ANd Tracking), toolkit[1] can be used for the fundamental particle interaction simulation including electron and X-ray transport. A simple Monte Carlo algorithm consists in repeating similar process but with randomised starting conditions or events. In our case, photons emission direction is randomized isotropically, in Geant4. All the possible photons interactions are considered in simulation while allowing them to fall over water phantom. The incident X-Ray energy spectrum has been obtained using SpekCalc software[2] and fed in Geant4. Spectra obtained for Tungsten anode at tube potential of 100 KVp with 12 anode angle at air thickness of 1000 mm.

Objectives: Proposed work aimed to investigate the spatial distribution of radiation dose in water equivalent phantom induced by a diagnostic X-Ray unit and organ dose measurement so that diagnostic technique can be properly justified.

Materials and Methods: Geant4 (version 4.9.6.p02)[3] has been used for simulation which takes into account coherent and incoherent scattering, photoelectric effect, Compton effect, bremsstrahlung for photon transport. Geant4 is a set of libraries providing tools to perform simulations. It is programmed in C++ and follows an object-oriented philosophy. For data analysis, in scientific framework ; ROOT (version 5.36/34) [4,5] has been used and integrated with Geant4. Geometeric construction of water equivalent phantom is constructed in Geant4 along with material information. For the dose calculation, X-ray spectra obtained by SpekCalc is fed in Geant4 as a energy generator of RADspeed X-Ray unit.

Results and Discussion: Absorbed dose at various positions in phantom has been calculated. It is to be verified with experimental data which is future prospective of our study. A close match between simulated and actual dose deposition is expected, results will be presented in conference.

   P-190: High Terrestrial Gamma Radiation Dose Rate Measured in Granite Geological Types; A Case Study in District of Kuala Pilah, Malaysia Top

Nor Eliana Norbani1, Nazaratul Ashifa Abdullah Salim2, Amin Aadenan1, Ahmad Taufek Abdul Rahman1,3

1Faculty of Applied Sciences, Universiti Teknologi MARA, 3Institute of Science, Universiti Teknologi MARA, Shah Alam, 2Malaysian Nuclear Agency, Bangi, Selangor, Malaysia. E-mail: [email protected]

Naturally-occurring radioactive materials (NORM) are all minerals and raw materials that contain radioactive nuclides of natural origin. These elements have always been presence in the Earth's crust and atmosphere. NORM concentrations can be altered through industrial activities such as coal, metal and mineral mining, fertiliser's production and usage, oil and gas production, building construction and recycling process. Some of these activities discarded the waste to water streams and alter the NORM concentration, known as the technologically-enhanced NORM (TENORM). It is important to have a fundamental baseline data for the radiation exposure of human to NORM across a geographical area to estimate dose received by the population. We have measured terrestrial gamma radiation dose-rates (TGRD) from surface soils throughout accessible areas in the district of Kuala Pilah, Malaysia. Dose rate measurements were carried out using a NaI (TI) scintillation survey meter, encompassing 214 locations, covering about 71% of the 1047 km2 of the land area Kuala Pilah district. This has allowed development of a TGRD contour map, plotted using WinSurf software. TGRD measured in the district of Kuala Pilah varies from 143 ± 7 nGy h-1 to 857 ± 15 nGy h-1. Higher TGRD were found at the area covered by soil type is Riverine-Local Alluvium Association . These soil types of high TGRD level are underlay by Undifferentiated Granit Rocks geological formations. The lowest TGRD measured was found in Acrisols and Ferralsols soil family which were underlay by Permian geological structure. The mean TGRD measured is 458 ± 13 nGy h-1 compared to a mean value of 92 nGy/h and 59 nGy/h for Malaysia and the world, respectively. The average annual dose from such TGRD to an individual in Kuala Pilah district, assuming a tropical rural setting is estimated to be 0.93 mSv y-1, which is considered to be within the normal range for doses from natural sources. The results can be considered as base values for distribution of natural radionuclides in the region and will be used as reference information to assess any changes in the radioactive background level due to geological processes and industries activities.

   P-191: Monte Carlo Simulation of Concrete Activation in Medical Cyclotron Vault Top

Biju Keshav Kumar, Anil Anant Shanbhag, Deepak Sakharam Joshi, Tapas Bandyopadhyay

Division of Health Physics, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Medium energy proton accelerators are used for the production of PET and SPECT radioisotopes. 30 MeV proton cyclotron for medical use is being commissioned in VECC, Kolkata for this purpose. The secondary radiations, neutrons and gammas needs to be shielded adequately to protect the personnel working around and the public. In addition to this, the induced activity of the accelerator components and the concrete structure by neutrons is also one of the major safety concerns during maintenance and decommissioning of the installation. The build-up of induced radioactivity in the structural material over the years and the resulting gamma dose rates exposes the workers during maintenance operations.

Objective: This study aims to simulate build up of the long lived radionuclides induced in the Portland concrete walls and dose rates with 10 ppm of trace elements of Cobalt and Europium of a typical 30 MeV cyclotron vault over a period of 4 years of operation. It is assumed that the accelerator operates for two shifts (16 h) followed by one shift (8 h) shutdown in a day.

Materials and Methods: This study makes a Monte Carlo simulation of a virtual medical cyclotron vault of dimensions 8 m x8 m x 6 m with 100 cm thick walls of Portland concrete. A trace level of 10 ppm of Cobalt and Europium is assumed in the Portland concrete composition. A pencil beam of protons of 30 MeV, 1 microampere falling on the thick stopping target is modelled at the centre of the vault with the proton irradiation profile, as mentioned in the objective. Copper and aluminium are two important materials commonly used for beam line fabrication and slit holders. Tantalum is used for beam current measurements in proton accelerators. These are the beam loss materials considered in the simulations. Simulations are made using a validated Monte Carlo code FLUKA2011.2C.5. Fluka is capable of making predictions about residual nuclei produced in hadronic and electromagnetic showers and time evolution of the radionuclide inventory calculations online. The isotope production and decay as a function of irradiation time and cooling time is calculated analytically using the Bateman equations by the code.

Results and Discussions: The neutron yield from the target material obtained by this study is 2.13E-2 per proton of the beam. This value is agreeing well with the value 2.0E-2, reported in the IAEA TRS-283 report.2 m x 2m slab of 10 cm thick layers of concrete along the depth are the scoring volumes. The centre of the scoring slabs coincides with the beam direction. It is observed that the major long lived gamma emitting radionuclides produced by the (n, gamma) reactions in the concrete are Co-60, Eu-152, Eu-154, Na-24 and Na-22. Individual concentrations of the above mentioned radionuclides in the front wall are presented in [Table 1] respectively after 4 years. The gamma dose rate at 1 m from the wall at the end of irradiation is 743 microSv per hour. This dose rate comes down to 10 microSv per hour after one week cooling, due to the decay of Na-24 isotope. The production and build-up of these long lived radionuclides and dose rates are studied as a function of irradiation time as well as the depth in the concrete.
Table 1: Induced radioactivity of long lived gamma emitting radionuclides

Click here to view

   P-192: Quality Management Of Radiotherapy Department Using Failure Modes And Effect Analysis Top

P. Nagendran, V. Poopathi, Jibak Bhattacharya, Saibal Mukherjee

Department of Radiation Oncology, Apollo Gleneagles Hospitals, Kolkata, West Bengal, India. E-mail: [email protected]

Introduction: Hospital is one where defects and mistakes are not and cannot be tolerated. A mistake could cost a patient their life. This means processes need to be in place and followed exactly how they are set forth to eliminate mistakes. In our radiotherapy department we have implemented Six Sigma project work using FMEA and avoid some issues and improved quality of treatment and new procedure. FMEA is a systematic method of identifying and preventing procedure and process problems before they occur.

Purpose: Improvement of Treatment Quality.

Aim and Objectives: Aim of the FMEA is avoid prevention of tragedy and doesn't require previous bad experience. Six Sigma certification is the best requirement in a healthcare environment for employees dealing with critical patient information. Quality improvement methods are more difficult to implement in a healthcare institute. The comprehensive approach offered by a Six Sigma Certification allows for the methodologies to be successfully implemented with positive results.

Materials and Methods: There are five steps of FMEA below mentioned here.

Step 1: Definition of Process: This FMEA is focused on Radiotherapy process and we have chosen only 11 Topics with team members. The radiotherapy treatment process is complex and involves multiple transfers of data between professional groups and across work areas for the delivery of radiation treatment. A minimum of three professional groups are needed for successful and safe treatment.

Step 2: FMEA Team: FMEA Number: 01; Date: Jan 2016 to December 2016; Team Members: 05.

Step 4: Hazard Analysis and Step 5: Actions and Outcomes are tables and graphically defined and analyzed errors.

Result and Discussion: We have collected all data, analysed and rectified in our department and compared with FMEA 2011, 2014 and 2016 years.

Conclusions: Improvements made in the department:

  1. Introduced HIS and the patient name and UIHID are printed out on stickers. The stickers are pasted on file
  2. Introduced workflow management software in Radiation therapy (Varian Medical System ARIA 11 ie version ECLIPSE 11) to do all the steps in radiation treatment from CT scan to treatment approval through the software. This has enabled a smooth workflow and reduced the chance of missing any step in the course of simulation and planning with periodically.
  3. Patient prescription is part of the workflow and is done through the software. Only approved prescriptions will go to the Physicist for planning
  4. Introduced time out form to reduce the probability of any wrong site radiation therapy
  5. Barcode scanner is used for scanning of patient card to open an approved plan so that the correct patient and the correct procedures are done automatically without manual intervention.
  6. Repeat CT scan reduced (wrong site avoid, mould fitting correctly)


Future Goals: We are planning to improve the current year data error rectify and so many new plans to implement in our department. Etc…

   P-193: Medical Physics Education and Clinical Training Program in Bangladesh Top

Kamila Afroj Quadir

Bio-Science Division, Bangladesh Atomic Energy Commission, Bangladesh. E-mail: [email protected]

Introduction: The number of medical physicist working in diagnostic and therapeutic facilities requiring medical physicists is disproportionately low in Bangladesh. There are around 30 hospitals that have radiotherapy department and 20 hospitals having nuclear medicine department. The number of medical physicists in oncology is 35 and 14 in nuclear medicine. There are no medical physicists working in diagnostic radiology. Two universities, one public and the other private, have medical physics degree program. These degree programs include B.Sc., M.Sc. and Ph.D. However, university programs are not coupled with adequate clinical training.

Objective: Medical Physicists in their specializing field who can confidently work unsupervised within a multi-disciplinary team with safety and high professional standard need clinical training.

Approach: International Atomic Energy Agency (IAEA) under the project “Strengthening of Medical Physics through Education and Training” developed guidebooks for clinical training for medical physics working in, Radiation Oncology (TCS-37) Diagnostic Radiology (TCS-47) and Nuclear Medicine (TCS-50). These clinical training guidebooks were designed to be relevant for all modalities irrespective of the level of equipment complexity in use in the RCA member countries. Bangladesh started its first clinical training program in nuclear medicine in 2011 by following IAEA TCS-50. This 2 years structured clinical training program was completed successfully. The medical physicists, (4 Residence), who qualified in the clinical training program were evaluated by IAEA expert by written, practical and oral examination. These qualified Residents were subsequently tested and certified by the Bangladesh Medical Physics Association. Clinical training program for medical physicists commenced again in 2016 organized by IAEA/RCA project “Strengthening the Effectiveness and Extent of Medical Physics Education and Training” through the e learning platform (AMPLE) and with medical physicists from both radiotherapy and nuclear medicine discipline. Ten (10) medical physicists working in radiotherapy and six (6) medical physicists working in nuclear medicine are taking part in this program. The radiotherapy Residents are following IAEA guide book TCS-37 while the nuclear medicine Residents are following the IAEA guide book TCS-50.

Conclusion: It is expected that in future accreditation will become a basic requirement for all medical physicist operating in a clinical environment.

   P-194: Microdosimetric Measurements in Bhabhatron Telecobalt Installation Top

Arghya Chattaraj, T. Palani Selvam, Vandana Srivastava, Sandipan Dawn, Kishore Joshi1, A. K. Bakshi, D. Datta

Division of Radiological Physics and Advisory, Health, Safety and Environment Group, Bhabha Atomic Research Centre, Mumbai, 1Advacned Centre for Treatment, Research and Education in Cancer, Navi Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Radiation quality can be described by macrodosimetric quantities LET and absorbed dose. LET and absorbed dose are volume average quantity and does not consider random nature of energy loss along the track. LET cannot express energy deposition in a small volume where average number of interactions is of the order of one or less. Radiations which differ in the number of energy deposits, their magnitude and spatial distribution may cause different effects for the same absorbed dose. All these drawbacks are taken care in microdosimetry. Microdosimetry is a technique for measuring the microscopic distribution of energy in cellular or sub-cellular level. Tissue Equivalent Proportional Counter (TEPC) is widely used for microdosimetric measurements in radiations field to characterize the radiation quality in radiation protection and radiotherapy environment. In microdosimetry, a lineal energy distribution is related to Relative Biological Effectiveness. Lineal energy, y is defined as the quotient of the energy imparted (ε) to the matter in a volume by single energy-deposition event, by the mean chord length l− through that volume. The number of events with event size between y and y + dy is denoted by f (y ) and the expectation value of y is frequency mean lineal energy,.is dose probability density and the expectation value of y is dose mean lineal energy, ȳD which describes variance of energy deposition in a sensitive volume.

Objectives: This study was aimed at measuring microdosimetric lineal energy distributions at different locations of a Bhabhatron telecobalt installation as a function of field size. From the measured microdosimetric distributions, and were determined.

Materials and Methods: Indigenously developed Bhabhatron telecobalt machine was used for microdosimetric measurements. A 20 x 30 x 30 cm3 water phantom was kept at source-to-surface distance (SSD) of 80 cm. 10 cm x 10 cm and 25 cm x 25 cm field size were opened at SSD = 80 cm. 10 cm x 10 cm and 25 cm x 25 cm field size were opened at SSD = 80 cm. Walled spherical TEPC filled with tissue equivalent propane gas and capable of simulating 2 mm site was used in the measurements. The measurements were carried out at the locations: (a) Behind Maze Wall for 10 cm x 10 cm (open and wedge field) and 25 cm x 25 cm open fields, and (b) above ceiling for 25 cm x 25 cm field size.

Results and Discussion: The measured microdosimetric lineal energy distributions are shown in [Figure 1]. The peak of the lineal energy spectra for 10 cm x 10 cm wedged field and 25 cm x 25 cm open field are shifted towards higher y value compared to 10 cm x 10 cm open field. Depending upon the location of measurements, variations in and are observed as shown in [Table 1]. Such variation is attributed to beam quality and angular distribution of scattered photons present at the location. The measured and values are expected to be affected due to the thresholds of TEPC in the range of 0.3 - 0.5 keV/μm. Whereas for photons, the threshold value of y could be up to 0.01 keV/μm.
Figure 1:Graphical representation of variation in Lineal energy for different field size and location

Click here to view
Table 1: Measurement of microdosimetric lineal energy at different locations of a Bhabhatron-II TAW Telecobalt installation as a function of field size using TEPC

Click here to view

   P-195: Diurnal Variation of Indoor Radon Concentration In Wayanad District, Kerala Top

Reshma Bhaskaran1,2, C. D. Ravikumar1

1Department of Physics, University of Calicut, Thenhipalam, 2Department of Radiotherapy, Government Medical College, Kozhikode, Kerala, India. E-mail: [email protected]

Introduction and Aim: Among all the natural sources of radiation dose to mankind, inhalation of radon (222Rn), thoron (220Rn) and their progeny contribute about 50% of global effective dose. The concentration of radon indoors depends on the ventilation conditions. The present work studies the diurnal variation of indoor radon concentration in the mud houses of Wayanad district of Kerala.

Materials and Methods: The region of study is Bathery in Wayanad district. The active measurements were done using the state of the art equipment, the Portable Radon Monitor (SMART RnDuo), developed by BARC (Bhaba Atomic Research Center, Mumbai). The detector works on the principle of scintillation counter by scintillation with ZnS (Ag).

Result and Discussion: The active measurements were done for a period of five days in ten houses to study the diurnal variation. The indoor radon concentration varies from 22.47 Bq/m3 to 386.5 Bq/m3. The active measurements showed very good correlation with the passive indoor measurements (R = 0.99). It is seen that the concentration of radon reduces during the day time as compared to the night. The concentration keeps fluctuating. The maximum concentration of radon is found after midnight and in the early morning hours. In the house showing the highest concentration of radon, the value increased to as high as 1533 Bq/m3 at night. However, the concentration dropped to levels shown during the day time when the room had increased ventilation by keeping the door of the room open overnight. The maximum concentration of radon decreased by a factor of 5 when the door was kept open along with the window opposite to it in the corridor which opens to the outside environment. The diurnal variation shows that the concentration of radon builds up at night when the ventilation in the houses is significantly reduced. The maximum concentration was found in the early mornings. Another room in the house was also studied using active measurements to check whether the concentration is the same in all the rooms. However, this room showed lesser concentration (average 161 Bq/m3). The room showing the highest concentration of radon had very large cracks in the floor. Due to the closed room, at night the temperature inside the room will be higher as compared to the outside environment. This results in stack effect, drawing the radon inside the room. The large cracks on the floor further assists in the flow of radon from soil gas to the indoor atmosphere due to the pressure variation between the indoor areas and the soil gas. Besides this the room has only one door giving entry to another room and not the outside environment. Hence lack of air circulation from the outdoor environment may also be contributing to accumulation of radon at night when the door was kept closed. As the second room has intact floors and the door of the room faces the outside environment the concentration of radon was not as high as seen in the first room. This shows that in spite of the source (concentration of radon in the soil gas) being the same, cracks and openings in the floor and walls contribute significantly to increase the radon concentration and hence the inhalation dose to the residents. It was found that the radon concentration in the houses in Wayanad district is higher as compared to the high background areas of Kerala.

   P-196: Practical Phantom Study Using Small-Type OSL Dosimeter Toward Direct Dose Measurement During Pediatric CT Examination Top

Tohru Okazaki1, Hiroaki Hayashi2, Emi Tomita2, Sota Goto2, Keiji Tada3, Yoshiki Mihara2, Natsumi Kimoto2, Ryosuke Kasai4, Yuki Kanazawa2, Vergil LE Cruz1, Takuya Hashizume1,5, Cheng Wei Hsin1, Ikuo Kobayashi1

1Nagase Landauer Ltd., Tsukuba, Ibaraki, 2Tokushima University, Tokushima, 3Faculty of Medicine, Shimane University, Shimane, 4Tokushima University Hospital, Tokushima, 5SOKENDAI, Shonan Village, Hayama, Kanagawa, Japan. E-mail: [email protected]

Clinical diagnosis using X-rays is a useful tool in finding abnormalities in organs noninvasively. However, radiation exposure raises the risk of cancer; thus, it is preferable to manage the exposure dose of each patient. The management of exposure dose is important especially for neonates and infants because their cancer risk is relatively high. A small-type OSL dosimeter, called nanoDot, has a small energy and angular dependences in diagnostic X-ray region and its detection efficiency is extremely low. We expected to use it for direct measurement of the surface dose on patients during Computed Tomography (CT) examinations. Our previous study using the neonate phantom showed that the nanoDot does not interfere with the CT image. Furthermore, the lower detection limit of a nanoDot was estimated to be less than 10 μGy, and it indicates the possibility to be used for the surface dose evaluation of exposure doses caused by scattering radiation. For example, the doses around the eye lens and the gonads during a chest CT examination can be evaluated. Therefore, we plan to use nanoDots for a clinical study in measuring surface doses. The aim of this study is to estimate the uncertainty of the directly measured surface dose related to the pediatric CT examinations in a phantom study. We used a volumetric scan mode of a 320-detector row CT (Toshiba Medical Systems), in which a scan length is 160 mm in one rotation of X-ray tube. The tube voltage was set to 80 kV and rotational speed was set to 0.275 s with the current 100 mA. For the CT examination, 13 annealed nanoDots were placed symmetrically on a neonate phantom (Kyoto Kagaku Co. Ltd.) from the head to the feet. First, we evaluated the influence of phantom positions on measured doses. One phantom placement is ±1 cm off-centered position from the center of scanning bed, and another is ±10 degrees rotated position. Second, the influence of wearing clothes on the exposure dose was examined. Exposed nanoDots were read with a portable-type OSL reader, called microStar (Landauer, Inc.). In the experiment, in which the phantom without clothes was placed at the center, the averaged measured dose of 6 nanoDots placed inside of the irradiation area was 2.7 mGy. On the other hand, the doses of nanoDots placed outside of the irradiation area concerning the gonads and the eye lens were estimated to be 0.27 mGy and 0.2 mGy respectively; these doses were less than or equal to 1/10 of the measured dose inside the irradiation area. We estimated the effect of wearing clothes, and the correction factor was estimated to be approximately 5% when nanoDots were placed on the clothes to measure surface doses. This result was caused by the decrease of scattered X-ray incident to nanoDots. From the experiments in off-centered positions, dose distribution of 6 nanoDots was evaluated. Although the position of the phantom was varied, the measured doses of nanoDots placed in a symmetric position and the averaged measured doses of each condition did not show a significant difference. These results show that the position of the phantom does not affect the measured dose during a pediatric CT examination. In conclusion, during a CT examination the surface dose of patients can be measured directly using the small-type OSL dosimeters. The OSL dosimeter can measure exposure doses both inside and outside the irradiation area. Additionally, we estimated the measurement uncertainty depending on the variation of the phantom settings and the presence of clothes. Based on the results, we will start a clinical study of directly measuring patient doses using nanoDots.

   P-197: Polymer Composites for Radiation Protection Top

R. Ambika, N. Nagaiah

Department of Physics, Bangalore University, Bengaluru, Karnataka, India. E-mail: [email protected]

X/Gamma rays find their increased applications in several areas of Science and Technology, for the benefit of mankind. From the past few decades, the nuclear techniques are being utilised for early diagnosis and treatment of several diseases. Radiation therapy (Internal and external) is one which uses X/Gamma rays, electron beam or proton to kill cancerous cells. Exposure to high energy radiations such as X/Gamma rays beyond certain limit, will definitely affect the normal tissues resulting in several radiation hazards. Hence, protecting from radiation exposure plays a crucial role in the radiation environment through proper shielding with the knowledge of shielding parameters. The common shielding material in use is lead, which is toxic, heavy and lack in usage flexibility. While, polymer composites have now added an advantage of being light weight in addition to their shielding ability. The present study deals with evaluation of shielding efficiency of polyester based composites filled with oxides of bismuth and tungsten for 80, 662, 1170 and 1332 keV gamma photons. The polymer composites with two different fillers Bi2O3 and WO3 were prepared by open mould cast technique by varying the additive weight %. The filler dispersability was confirmed through scanning electron microscopy technique. Gamma shielding measurements were performed using a gamma ray spectrometer with a narrow beam geometry set up. The shielding parameters such as attenuation coefficient, half value layer thickness, effective atomic number (Zeff) and electron density (ne) were evaluated. The results reveal the dependency of linear attenuation coefficient on density, Zeff, ne and energy of the gamma photons. Density, Zeff, ne of the polymer composites have been increased due to the addition of filler concentration to the polymer matrix. Upon increasing the filler weight % in both the composites, the linear attenuation coefficient was found to increase considerably. Of which, 50 wt% filled composites possess maximum attenuation coefficient. This may be attributed to the presence of high metal oxide Bi2O3 and WO3 in the matrix, as high Z metal is responsible for the photon interaction in the material medium. Further, the probability of photon interaction with the medium is also dependent on incident photon energy. It is clear from the present study that, as the energy increases, interaction cross section decreases resulting in decrease in the attenuation coefficient. The attenuation coefficient is high at low photon energy say 80 keV when compared to high energy, as the probability of photoelectric absorption is high for the energy less than 100 keV. The shielding parameter, mass attenuation coefficient is very important to evaluate and assess any material as an excellent radiation shield, as it is density independent. It was found to be high for the tungsten oxide filled composite for 80 keV gamma photons when compared to bismuth oxide filled composite. In the case of Bi2O3 filled composite, the formation of absorption edge at 90.5keV, where complete absorption takes place may be the reason for the decrease in the attenuation coefficient at 80 keV. Further, half value layer thickness which is required for the practical appliance was found to be very low for both the composites and is 0.32 cm and 0.11 cm respectively for Bi2O3 and WO3 filled composites at 50 Wt %. Both the composites are appreciable in terms of shielding ability. However, the shielding efficiency of the 50 wt% Bi2O3 filled polymer composite is almost comparable to barite at 662 keV, whereas, 50 wt% WO3 filled polymer composite perform better than lead at low energy. Hence, these composites can be used in different forms by the medical radiation practitioners/professionals for protecting themselves and the patients from the exposure of X/Gamma rays.

   P-198: Structural Radiation Shielding Design of Gamma Knife Facility Top

Smriti Sharma, G. Sahani, Pankaj Tandon, A. U. Sonawane

Division of Radiological Safety, Atomic Energy Regulatory Board, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Gamma knife equipment used to deliver a single high dose fraction of radiation, from 192/201 cobalt-60 sources which are distributed over a hemisphere. Centre of the hemisphere where radiation beams from these sources are focused is called focal point. Gamma knife equipment is designed for maximum capacity of total activity ~6000 Ci of Co-60. Bunker housing Gamma Knife equipment need to be provided adequate radiation shielding so that radiation exposures to members of the public and occupational worker not exceeding stipulated radiation dose limits. In order to achieve the goal, this paper focused on shielding calculation of bunker housing Gamma Knife equipment. Institutions desirous to start Gamma knife facility required to obtain layout plan approval from Atomic Energy Regulatory Board (AERB), national regulatory body, prior to construction. This work will be useful in preparing standard layout drawing which will further guide user institutions for preparing layout drawing for Gamma Knife facility to obtain layout approval from AERB. Hence, it may be helpful to avoid multiple rejection of layout plan application.

Objectives: The objective of this paper is to work out shielding thickness of a bunker having minimum required inner dimension to house gamma knife equipment.

Materials and Methods: Manufacturer of Gamma Knife is Elekta Instrument AB Stockholm, Sweden. The Gamma knife model Type B/C/4C and Perfexion are available in the country and one model is upcoming. Out of these, Type B/C/4C models are obsolete and no longer available for new installation and commissioning. Shielding calculation for Gamma knife installation is complex due to highly anisotropic radiation around the unit. Hence, dose map around the equipment is primarily required for shielding calculation. Manufacturer has provided dose map for Perfexion and new upcoming model for the Beam ON/OFF condition and with/without phantom. Dose map was provided in both horizontal and vertical plane at grid spacing of 0.5 m (along x, y, z directions). As per the manufacturer, radiation level was measured and then rescaled for maximum design capacity. For determining shielding thickness, workload is key factor to be first determined. Workload is defined as total dose delivered per week at isocenter or weekly Beam ON time considering maximum number of patient treated in a week. In this study, we have considered weekly Beam ON time as workload of the facility. Workload of the facility was determined by assuming 6 min/target, 5 average number of targets/patient, 5 patients treated/day and 5 working days/week. Based on above assumption, estimated workload comes out to be 12.5 hrs/week. Use factor and occupancy factors were taken to unity. Minimum inner dimension of the treatment room provided by manufacturer is 6.5m (L)×4.6m (W)×2.5m (H). However, considering the futuristic approach e.g. to house other radiotherapy equipment (Telecobalt, Accelerator etc.), inner dimensions 7.0m (L)×6.0m (W)×3.0m (H) were considered for shielding calculation of Gamma Knife facility and it was used for preparation of standard layout. Minimum distance between the unit focal point and the wall back side of the Gamma Knife was taken 2 m and that of opposite wall at 5m. Minimum distances of the walls along width were taken 2m and 4m on either side of focal point.

Results and Discussion: Using the dose map and optimizing parameters such as beam ON time, use factor and occupancy factor, radiation shielding thickness of the walls/ceiling comes out to be less than that of the required for earlier models of Gamma Knife. Moreover, manufacturer standard plan stated the shielding thickness around 60 cm of concrete. Hence, to prepare standard layout plan it was decided to keep the shielding thickness 60 cm of concrete depending upon near future extension for another type of equipment.

*Authors are thankful to Elekta Medical System, Sweden for support for the study.

   P-199: Radioiodine I131 Patients Release Criteria in Dubai Health Authority Top

N. A. Boshara, M. M. Zakaria, L. G. Albalooshi

Medical Physicist, Dubai Health Authority, Dubai, UAE. E-mail: [email protected]

Radioiodine therapy is well established as a treatment for thyroid cancer because of its radioactive proprieties; radioiodine decay by emitting high energy Beta particles that interact with mater in short distance. This interaction results in depositing energy locally within the patient tissues. From a radiation safety perspective, this radiological practice should be optimized to ensure radiation safety of staff, the public and care providers during handling excretions and patient's body fluids. A total of 391 Patients in Dubai Hospital, Dubai Health Authority, United Arab of emirates, received I-131 high therapy doses for thyroid cancer treatment from January 2010 until December 2016. This study was conduct to review the patient release criteria in Dubai Health Authority. The study classified the obtained data into groups according to the administered dose as: Group A patient received I131 capsules with activities below than 100 mCi, Group B patient received activities between 100-150 mCi and Group C patient received activities above 150 mCi. For each group, administered dose, remaining activities and dose rate were calculated and recorded for an average age of 40 years old ranged between (16 and 73) years old. Approximately 80% of patients were females and 20% were males. More or less, 39% of these patients received up to 100 mCi (3700 MBq), I-131 Oral Doses, where the minimum and the maximum doses were 60 mCi and 97 mCi respectively. 42.7% of these patients received I-131 Oral Doses from 100 to 150 mCi. Minimum and maximum doses activity were 101.57 mCi and 137.54 mCi respectively. Moreover, 61% of patients received I-131 doses up to 150 mci (5550 MBq) fluctuated between 102 and 138 mCi. Both the NRC and the NCRP recommend releasing I131 patients from hospitals following the administrated activities and radiopharmaceuticals criteria. some of the neighboring Gulf countries that having the same social culture as UAE such as Oman releasing I131 patients with dose rate ≤ 70 μSv/hr. On the other hand, a number of international countries depend on the criteria of discharging I-131 patients, according to residual activity in the patient body since the patients released for discharge with residual activities less than 33 mci (1221 MBq). However, Dubai Hospital- DHA in UAE following IAEA recommended criteria for releasing patients with radiation dose rate at defined distance, the applicable radiation dose rate for discharge I-131 patients in DHA – UAE is 50 μSv/hr at 1 meter. The emitted radiation dose rate detected by ceiling-mounted detector (DLMon (Dose Rate Monitoring) System) fixed at one meter from the patient's bed. An average of three readings every two hours obtained and recorded in the system. Remaining Activity in patient's body estimated by using the below equation:

Remaining Activity (MBq) = A *EXP ((-0.693/T1/2)*T)

Patients released for discharge from Dubai Hospital-DHA with an average of 35 μSv/hr at one meter. Hence, this dose rate is equivalent to an average of 17 mci (633 MBq) as residual activities in the body. Accordingly, the applied criteria in DHA tolerate releasing of I131 patients with radiation dose rate lower than a number of other countries and within the recommended international limits (70 μSv/hr recommended by IAEA and 50 μSv/hr recommended by NRCO & NRC). Nevertheless, the common lifestyle and social culture in UAE may contribute in enhancing radiation protection for patient family and public.

   P-200: Pediatric Interventional Cardiology: A Literature Review on Radiation Doses Top

A. Ploussi, K. Platoni, E. P. Efstathopoulos

2nd Department of Radiology, University General Hospital “Attikon”, School of Medicine, National and Kapodistrian University of Athens, Athens, Greece. E-mail: [email protected]

Introduction: The increased frequency of interventional cardiology procedures in recent years, the radiation-related cancer risks, the high radiation doses delivered during interventional procedures as well as the increased radiosensitivity of children have raised serious concerns regarding the exposure of pediatric population to ionizing radiation. Moreover, as pediatric patients with congenital diseases often undergo multiple interventional cardiology procedures during their life, cumulative radiation dose may reach high levels.

Objectives: The purpose of the current study is to provide a literature review concerning radiation doses to pediatric patients undergoing interventional cardiology procedures.

Materials and Methods: A thorough literature search was conducted using the database PubMed for studies published between January 2000 and April 2017 with the following keywords: [children or paediatric] and [doses or exposure] and [nterventional cardiology or catheterization or angiography]. Only articles in the English language were included.

Results: The literature search identified a total of 39 relevant articles: 38 originals articles and 1 review article. The studies included diagnostic as well as therapeutic interventioanl cardiology procedures. Radiation dose measurements were performed either with physical measurements using pediatric anthropomorphic phantoms or using Monte Carlo simulation techniques. The articles included information regarding DAP, effective dose, organ dose and fluoroscopy time. Effective dose values ranged from 0.16 to 27.8 mSv for diagnostic and from 0.38 to 66.7 mSv for therapeutic interventional cardiology procedures. The highest radiation doses received by the heart, lungs, breast, esophagus and thyroid gland. The fluoroscopy time ranged between 0.3 and 47.8 min for diagnostic and between 7 and 75.1 min for therapeutic interventional cardiology procedures.

Discussion: The overview revealed large variations in the values of radiation dose even for the same type of interventional procedure. This can be attributed to three main reasons: i) the different technology of imaging equipment (eg. image intensifier vs flat panel detectors), ii) the wide range of body size in pediatric patients even for children of the same age and iii) the education of medical staff on radiation protection issues as well as the physician's experience. Reliable estimation of radiation dose and cancer risk faces many challenges in pediatrics. It requires standardization of the recorded dosimetric quantities, optimization of the clinical protocols, follow-up of the patients during their life and studies in larger cohort of patients.

P 201 ABS0291

   P-201: Categorization of Radiation Sources and Applicable Security Measures for Radiation Sources Used in Radiotherapy Top

B. Mishra, M. Mahesh, G. Sahani, Pankaj Tandon

Division of Radiological Safety, Atomic Energy Regulatory Board, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: The technologies that make use of ionising radiation sources (i.e. radioactive material and radiation generating equip.) continue to spread around the world as well as in our country. They are used in multifarious applications in various fields such as medicine, industry, agriculture, research, military, mining, academic applications, etc. This technology has been playing remarkable role in enhancing quality of life and plays significant role in improving or saving life by treatment of cancer and diagnosis of various diseases. Safety record of this technology is generally good, however, However, while attempting to address the threats from malevolent acts involving radioactive sources, it is clear that sources of certain magnitudes and types are more vulnerable to such acts than others. Therefore, it is felt that there is a need to adopt different security approach based on the potential hazard associated with the source and hence there is need of stringent regulatory control for security of radioactive sources.

Objective: Sources with high activity, if not managed safely and securely, could cause severe deterministic effects to individuals in a short period of time. The categorization provides an internationally harmonised basis for risk informed decision making. Based on these values different security measures has been considered.

Materials and Methods: A dangerous source is defined as a source whose activity is high enough to deliver a radiation dose which would result in severe deterministic effects in the exposed individual. The activity of a source, which can deliver this dose, is termed its “D value”. Both external and internal exposures are therefore considered in the derivation of D values and which is already established in the IAEA safety guide No. RS-G-1.9 and AERB safety guide on security of radioactive material i.e. AERB/RF-RS/SG-1 . There are five different categories based on the calculated value of the ratio i.e. “A/D” (Activity of the source” A” in Ci) value. For example Co-60, D value is 0.8 Ci and for a telecobalt source of the order of activity A~12000 Ci. The A/D> 1000 which falls under Category1 source. No categorization for radiation generating equipments. Considering security different security scenarios associated with radioactive sources, four security levels - A, B, C and D have been defined. These levels provide a systematic way of categorising the graded performance objectives required to cover the range of security measures that might be needed. The performance objectives for the four security levels of a security system are detailed below:

  • Security Level A: Prevent unauthorised removal
  • Security Level B: Minimise the likelihood of unauthorised removal
  • Security Level C: Reduce the likelihood of unauthorised removal
  • Security Level D: Measures should be established to ensure safe use of the source.

Conclusion: While addressing the threats associated with radioactive materials with respect to malevolent act/terrorist act and potential exposure with the source loss the principles of security measures: detection, delay, response and security management need to be implemented. During our review on the submitted security plans, it is revealed that there is a need to strength the security measures at Radiation Facilities (RFs). User need to design the security infrastructure based on perceived security threat addressing the issues in the security plan and register it with the Law & Enforcement Authority. Additional measures need to be augmented by establishing information exchange procedure with the Law & Enforcement authority. There should be separate detection system such as CCTV, intrusion systems, passive infrared systems integrated with response mechanism for 24×7 days instead of considering the CCTV which is available for patient monitoring during treatment. Access control systems must be implemented such as biometric, PIN based systems, swipe card systems etc. All security devices/systems need to be maintained periodically and quality control system need to be in place. The physical security system must address the detection time, delay time, and time required to initiate response and defeating the adversary. Administrative procedure must be in place defining clear role and responsibility. There should be a layout diagram indicating the access point, entry/exist to the facility and security infrastructure etc. Security measures shall be implanted at RFs to address the security threats and malevolent acts.

   P-202: Source on Position Leakage Measurement from Source Housing of Telegamma Unit Over the Period Of 36 Months – A Retrospective Analysis Top

N. Balasubramanian, V. Kaushal, Yogesh Kumar, N. P. Patel, Anil K. Dhull

Department of Radiation Oncology, Pt. B.D. Sharma PGIMS, Rohtak, Haryana, India. E-mail: [email protected]

Introduction: The aim of this study is to evaluate and analyze the on position leakage in-patient plane and radiation safety compliance of telegamma unit over the period of 36-months. RMM (Roentgen per minute at 1 meter) measurements and leakage radiation measurements in-patient plane are the part of the Quality assurance programme. Both measurements were repeated at regular intervals. These recorded values have been taken up to assess the shielding adequacy of source housing of telecobalt unit over the period of years. Measured values at 69.0 cm and 156.0 cm from the beam axis 8 points located in-patient plane ranges from 0.027% to 0.081% and 0.0045% to 0.0062% respectively, which were well below the specified tolerance limit of 0.1% RMM.

Materials and Methods: A new cobalt-60 source from BRIT (Board of Radiation Isotope and Technology) has been loaded on telecobalt machine and commissioned for patient treatment in the Department of Radiotherapy, Pt. B. D. Sharma PGIMS, Rohtak in the year 2014 after receiving authorization from the competent authority. As per the literature, the defined age of the 780E Teletherapy machine is 13 years. The recorded values for the years 2015, 2016 and 2017 have been taken up and evaluated. The gantry of telegamma machine was stationary at 0° and the collimator was closed fully with shielding blocks supplied by manufacturer during entire leakage measurements. For this leakage measurement, calibrated large volume pressurized ionization chamber based radiation survey meter from fluke biomedical model 451P-DE-SI-RYR with integrated mode was used. The great care must be taken to position the survey meter in such a way that patient plane is parallel to GM detector axis and perpendicular to radiation beam axis. During the measurement, chamber was positioned at 69.0 cm and 156.0 cm radius from the isocentre of the machine. The couch has been rotated carefully and the readings were recorded for different angular positions. [Figure 1] shows the measurement positions in the patient plane at two different radii. Calibrated Secondary Standard Fluke dosimeter coupled with 0.6cc ion chamber was used to carry out RMM measurement. The measured source strength was 169.233 RMM as on 29.09.2014. Percentage of source head leakage at various points were calculated[1] using RMM value measured at 1 meter along the radiation beam axis for 20 cm × 20 cm field size.
Figure 1: Measurement position in the patient plane at two different radius R1 = 69 cm and R2 = 156 cm

Click here to view

Results and Discussion: [Table 1] shows the measured percentage leakage radiation from the treatment head of telegamma machine at different angular positions in the patient plane at 69.0 cm and 156.0 cm away from the isocentre. As per national protocol,[1] the measured exposure rate at 1 meter from the source with collimator jaws closed completely blocked with appropriate lead thickness should be less than or equal to 0.1% of RMM of the loaded source. The recorded values are less than the tolerance limit 0.1% specified by the competent authority.[1] The source housing shielding is adequate for the cobalt telegamma unit installed in our center.
Table 1: On-position leakage from the source head of telecobalt machine (theratron 780E) in the patient plane for the last 3 years

Click here to view

Conclusions: From this retrospective analysis, the percentage on-position leakage from the source head of telegamma unit at various points was less than the tolerance limit recommended by the competent authority. The study results shows that the shielding adequacy of the source head over the period of time is adequate and improve the safety of the patient during the treatment and the telecoblat machine can be used for patient treatment safely.

   P-203: Estimation of Radiation Exposure to Technologist During 18F-FDG PET/CT Procedures at Our Centre Top

M. S. AL-Aamri, N. K. AL-Balushi

Department of Nuclear Medicine, Molecular Imaging Center, Royal Hospital, Muscat, Sultanate of Oman. E-mail: [email protected]

Introduction: Positron Emission Tomography (PET) is the imaging modality of choice in oncology. In addition, there are several indications for using PET in cardiology and neurology. The main radiotracer used is the radiolabeled glucose analog 18F-FDG (Fluro Deoxy Glucose). The high-energy annihilation radiation from positron emission may leads to significant radiation exposure to professionals, patients and their relatives.

Objectives: In this cross sectional observational study, we have assessed the effective dose to workers in Molecular Imaging Center (MIC) from patients injected with 18F-FDG.

Materials and Methods: Dose rates were estimated by calibrated (Ludlum14 C model, pancake GM external detector, USA), portable gamma ray survey meter at 0.300, 0.500, 1.000 and 2.000 m from 70 patients who undergo whole body 18F-FDG PET/CT procedure immediately and 2 hours' post injection. Electronic Personnel Dosimeters (EPD) (Rados) were used to determine the radiation doses per PET/CT imaging for the five staff involved in and directly handing the injected patients; two technologists, two staff nurses and one medical physicist.

Results: The mean dose rates from patients after injection and standard deviation for the four distances were 98.120 ± 24.000, 55.263 ± 15.000, 28.234 ± 10.500 and 10.806 ± 5.000 μSv/h respectively. After 2 hours, the measurements significantly dropped to 45.734 ± 13.000, 23.649 ± 10.000, 9.934 ± 4.000 and 3.749 ± 1.000 μSv/h.

Conclusion: The average effective dose values for workers from injected patients throughout the procedure of PET/CT study were less than 20 mSv/year which is the limit recommended by the International Commission on Radiological Protection (ICRP).

   P-204: Operational Experience with E-Licensing of Radiation Application for Radiotherapy Practice Top

B. Mishra, G. Sahani, Pankaj Tandon, A. U. Sonawane

Division of Radiological Safety, Atomic Energy Regulatory Board, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: eLORA is a web-based I&CT (Information and Communication Technology) application establishing communication between Atomic Energy Regulatory Board and its stakeholders (i,e Radiation Facilities, Supplier, Manufacturer etc.) for exchange of information and communication for delivering its regulatory services.

Objectives: The eLORA system is designed to automate the regulatory submissions, to achieve transparency and better efficiency in regulatory system. The components of eLORA are chosen to ensure Security, Performance, Availability, Scalability, Manageability and Maintainability.

Materials and Methods: The objective of eLORA is to reengineer the paper application forms to electronic submissions. Periodic update at institutional level (such as details of staff members, safet/QA instruments etc.) which affects application submission/process has been separated out for simplicity and better efficiency. System is constructed with more business logic for regulatory activities. On the same platform during the design phase the scalability has been consider significantly to construct all regulatory practice. Various regressive test such as factory acceptance test, pre-user acceptance test, user acceptance test are carried out before implementing the system.

Results and Discussion: [Table 1] represents data for more than 4 years in this analysis for efficiency, productivity and reliability of the eLORA system. It is noted that, during the paper based regulatory process, RSD, AERB used to receive ~18,000 submissions annually. From the Table-1 it is clear that the submission has reached almost four fold. In the same time, there is no enhancement in staff members at the Division. Some of the application details are considered for representation as below.
Table 1: Analysis for efficiency, productivity and reliability of the eLORA system using data of 4 years online application submission

Click here to view

Institute Registration: This is a new step introduced in eLORA for registering the authenticated information about the institution. During the initial phase, there is a tremendous increase of these applications as all existing RFs are switching to eLORA system. Around 32,000 institutes are now under regulatory purview through eLORA. The rejections of the submitted applications are due to the data inconstancy, inappropriate documents. The approval ration can be enhanced by referring the guidelines before submission.

Radiological Safety Officer (RSO): The trend of RSO applications were maximum during 2015-16 as existing approved RSOs getting migrated to the system and more number of institutes started using the system. The rejection shows the lower trend with respect to the preceding years and mainly attributing for PMS availability and appropriately updating the qualifications of registered Radiation Professional.

Regulatory Applications for all practices: It is noted that 234,006 number of applications has been submitted in the system, which clearly indicates the consistency and reliability of the system. The rejection indicates a decreased trend. It is mainly attributing in easy submission process, simplified regulatory procedure and further it can be drastically reduced by verifying the application submission through different tabs as provided in the in the application page.

Regulatory Applications for Radiotherapy (RT) Practice: Regulatory form submission as applicable to RT practice has shown reduced rejection over the preceding years. Typically it is noted that the major rejections are in response to non-compliance and inconstancy in transport applications.

RT-Layout Plan: In the site and layout plan submission for radiotherapy practice has shown an increasing trend in the preceding years because of regularisation process for the existing bunkers. It was further observed that the rejection is more in comparison to the approvals. It can be reduced by referring the guidelines specially prepared for preparation of site and layout purpose and can downloaded from the help menu.

RT-Procurement: The source and equipment application shows a clear trend in decreased rejection. It is mainly attributed toward the clear understanding of regulatory requirements from the user end as the regulatory process built in eLORA are simplified. Further, it can bereduced by re verifying the institute details for availability of adequate staff members, availability of adequate QA/Safety/Measuring and Monitoring tools before submission.

Recently, performance level upgrades are going on which will ensure the availability of the system 24x7 days.

   P-205: Quantitative Analysis Of Ayurveda Drug By Comparative Study Of Kasisa Bhasma Using Atomic Absorbption Spectrometric Technique Top

A. Ashwini, S. S. Teerthe, B. R. Kerur

Department of Physics, Gulbarga University, Kalaburagi, Karnataka, India. E-mail: [email protected]

Introduction: In Ayurveda bhasma (calx) is a drug used for therapeutic purpose by different practitioners since centuries. Preparation of bhasma includes various processing steps like purification, levigation, calcinations cycle, improving quality and removing blemishes etc, processing of bhasma aims at formation of herbo-mineral complex molecule which can act in minimal dosage, palatable, easy for assimilation, highly efficacious with minimal or no complication. Now a day different brands bhasma are commercially prepared and available in market being used by patients, but contamination of ayurvedic drugs with trace elements is major concern and the poor quality of these medicines causes health hazards. Hence is necessary to know the levels of major, minor and trace elements present in the ayurvedic drugs. In this direction in present work studied the elemental concentrations of Kasisa bhasma manufactured by four branded firms and analysis is carried out using AAS.

Materials and Methods: In the present study four brand Kasisa bhasma (drug) selected and labeled such as AKB, BKB, PKB, and DKB. The drug sample solution is prepared as per standard solution preparation for Atomic Absorption Spectroscopic technique. Elemental analysis is carried out by the Thermo Scientific range of ICE 3000 series Atomic Absorption Spectrometer (AAS). Atomic Absorption Spectrometer is an analytical instrumentation technique used in determination of metal concentration in sample which is in solid or liquid form. Atomic Absorption (AA) occurs when a ground state atom absorbs energy in the form of light of a specific wavelength and is elevated to an excited state. The amount of light energy absorbed at this wavelength will increase as the number of atoms of the selected element in the light path increases. The relationship between the amount of light absorbed and the concentration of analytes present in known standards can be used to determine unknown sample concentrations by measuring the amount of light they absorb.

Result: Presented in [Table 1] and [Figure 1].
Table 1: Quality Management of Radiotherapy Department Using FMEA

Click here to view
Figure 1: Elements concentration in mg/l versus elements in the Kasisa bhasma

Click here to view

Discussion: The estimated concentrations of Mg, Al, K, Ca, Mn, Fe, Cu and Zn are presented in [Table 1]. From the [Table 1] and [Figure 1] observed that Kasisa bhasma is iron rich drug in ayurveda which is used in anemia treatment and in treatment of eye diseases, leucoderma, primary and secondary amenorrhea. All four brand drug showing little variations in the concentrations of all elements.

Conclusion: This result revealed that the Kasisa bhasma is rich in iron. Ca, Mg, Mn, Zn and other element are found, though the drug of all brand are shows small variation in elemental concentrations but these elements found within the rate of Recommended Daily intake of minerals and vitamins in food as recommended by WHO. Thus present work is comparative study will reflect quantitative analysis of Kasisa bhasma.

Acknowledgment: The authors express their sense of gratitude to UGC-BSR for providing financial support.

   P-206: 'Mock Trial' on Patient Release During 'Source Stuck' in a Clinical Telecobalt Radiotherapy Machine and Estimates of Stray Radiation Exposures Top

Ramamoorthy Ravichandran

Cachar Cancer Hospital and Research Centre, Silchar, Assam, India. E-mail: [email protected]

Radioactive cobalt-60 teletherapy machines still find a place in radiation therapy departments, in more populated and developing countries. Radiation safety text books and protection safety guides of different nations give guidelines how to react at a situation, but so far, there are no reports how these are executed practically. There is no documented method, how a technologist will approach problems of this nature, when the patient wears an immobilization shell. The Radiological Safety Officer (RSO) has to display sufficient warning instructions and the actions to be followed in terms of emergency situations, such as “source drawer stuck ON position” or “not going fully back to OFF position.”A “mock trial” “source stuck” was simulated by keeping the machine is in OFF condition. A human dummy model (Medical Mannequin) was kept on the treatment table for demonstration. Two radiation technologists carried out the above exercise to release the clamp on the “Orfit” Base Board, table top operations, and the actual duration is recorded with an electronic stop watch as a mean of two attempts. A condenser chamber type “calibrated pocket dosimeter” (Model 909, chamber 242952) (Arrow-Tech Inc., USA) was used to estimate the doses at known location inside the room. Cumulated doses were estimated at a position 1.45 m radially away from “source,” which corresponded to the location of a technologist standing and operating the hand control. The pocket dosimeter had a water can to provide back scatter. Stray doses with and without scatter water phantom at 0°,90°, and 270° positions of the gantry. For lateral beam, the recorded dose rates were 72.4–37.2 μGy/min with and without water phantom. Same lateral beam with machine head on the opposite side had 35% increased exposure rate due to forward scatter, i.e., 98 μGy/min against previous value of 72.4 μGy/min. It reveals the presence of more forward scatter in the gamma beam. In this position, when the phantom is not there, the exposure rate at the radial location increases from 98 μGy/min to 114.0 μGy/min (increase of about 16%). This implies that unattenuated primary initiates increased scatter from the opposite concrete barrier wall, thereby increasing the stray radiation dose level. Effect in the vertical beam results in an exposure rate of 147.2 μGy/min with phantom present, which reduces to 86.8 μGy/min (a reduction of about 41%) when phantom removed. From above measurements, if we normalize the values for a nominal source activity of 333 TBq (9000 Ci) and 30 s duration (assumed as patient releasing time by technologist), the resultant personnel dose in these situations vary from 63 μGy to 267 μGy (6.3–26.7 mR). As part of the time in these estimations is for “presence of primary” and later only scatter, the actual exposures will be nearer to 63 μGy (6.3 mR). CD dosimeter estimated a leakage of 2.2 cGy/h at 89 TBq, which will correspond to 1.8 mGy/min if the collimator is totally closed (as in the case of Bhabhatron machine) when the technologist will be exposed to only leakage radiations as the primary is shut off. In this present report, the true situation encountered in a cobalt-60 teletherapy installation is simulated, and a possible management strategy is arrived at. This work is likely to remove the apprehensions on the use of telecobalt machine, and might continue give preference as a practical solution in addition of armamentarium for cancer radiotherapy in busy centres.

   P-207: An Enhanced Ionising Radiation Monitoring and Detecting Technique in Radiotherapy Units of Hospitals Using Wireless Sensor Networks Top

Peter Ali

Department of Physics, Ebonyi State College of Education, Ikwo, Nigeria. E-mail: [email protected]

In this paper, a solution of ionising radiation monitoring based on the concept of Wireless Sensor Network (WSN), is presented. Radiation dose rate measured by the sensor node is sent to the monitoring station through ZigBee wireless network operated on 2.4 GHz unlicensed Industrial Scientific Medical (ISM) band. The system is calibrated for use for ionizing radiation dose rate range of between amount of ionising radiation observed in radiotherapy unit of a hospital and 1.02 mSv/h. Power consumption of the sensor node is kept low by operating the node ZigBee radio with low duty cycle: i.e. by keeping the radio awake only during data transmission/reception. Two ATmega8 microcontrollers, one each for sensor node and the monitoring station, are programmed to perform interfacing, data processing, and control functions. The system range of coverage is 124m for outdoor (line of site) deployment and 56.8m for indoor application where 5 brick walls separated the sensor node and the monitoring station. Range of coverage of the system is extendable via the use of ZigBee router(s).

   P-208: Nuclear Emergency Preparedness in Atertiary Care Hospital Top

Deboleena Mukherjee, Arti Sarin1, Sachin Taneja, Kirti Tyagi

Radiation Oncology Centre, INHS Asvini, 1Department of Nuclear Medicine, INHS Asvini, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: Disasters are mainly classified into two types natural and man-made. Natural disasters are weather or earth related namely floods, cyclones, hurricanes, landslides, earthquakes, drought, famines and volcano eruptions etc caused due to natural impact on the environment. Man-made disasters are nuclear, biological and chemical nature either caused by accidents or by terrorist activity. Worldwide, there is an increased use of radioactive materials in industrial, medical, agricultural and other scientific research activities leading to a measurable increase in natural background radiation levels. Accidents in nuclear power plants (NPP), medical or industrial facilities that use radiation or nuclear weapons and constant threats by militants of “dirty bomb” are always a cause of concern and therefore a comprehensive “nuclear emergency preparedness” is of utmost importance. Being a tertiary care hospital, this need is further enhanced for safeguarding the human and animal life in sea, land and air of our country in case of any such disasters. In this paper we will discuss the response plan in case of “nuclear emergency” by this hospital.

Materials and Methods: To handle mass casualties, as per the guidelines a Nuclear Biochemical Cell (NBC) comprising of medical super specialist officers cum RSO, nursing staff and trained personnel has been formed to monitor, decontaminate, cleanse and treat the causalities in case of any emergency related to Chemical, Biological, Radiological and Nuclear (CBRN) disasters. A wide range of NBC protection materials and equipment like NBC suits, protecting gloves, masks, respirators, medicines, radiation survey meters, contamination monitors, gamma zone monitors and personal monitoring devices are procured (available). All protection instruments are periodically checked and calibrated at Defence Research Laboratory (DRL), Jodhpur. As per AERB guidelines, a local committee on radiation safety has been appointed and frequent mock drills and meetings related to emergency preparedness are carried out at this hospital.

Results and Discussion: A comprehensive emergency preparedness procedure and response plan is a necessity in our country. The main role of CBRN decontamination centre is to detect contamination, monitor, and segregate and to carry out the decontamination and treatment of casualties due to toxic agents (chemical, biological, radiological and nuclear) using appropriate means as per IAEA, AERB and National disaster management guidelines. Such procedures have to rely on extensive instrumentation support for efficient and viable counter measures. Every individual should act like a responsible citizen during any emergency and a strict security system and alertness should be followed in our country to avoid such an emergency.

   P-209: Analysis of Excessive Exposure Cases of Radiation Workers in Medical Field Top

Kirti Tyagi, Deboleena Mukherjee, P. B. Mukherjee

Department of Nuclear Medicine, INHS Asvini, Colaba, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: The main objectives of monitoring radiation workers is to ensure that exposure are kept as low as reasonably achievable (ALARA). In India Atomic Energy Regulatory Board (AERB) is the national regulatory body and as per their directives the lifetime cumulative effective dose constraint for five years shall be 100mSv i.e average 20 mSv / year - five year block, however, whole body equivalent dose shall not exceed 30mSv in any one year.

Objectives: The purpose of this study is to analyse the cause of reported excessive exposure cases in various department dealing with radiation units and radiation sources.

Materials and Methods: Medical X-ray facilities avail Personnel Monitoring Service (PMS) for their radiation workers from Bhabha Atomic Research Centre (BARC) accredited laboratories on quarterly basis. The institutions and radiation workers are registered with National Occupational Dose Registry System (NODRS). The accredited labs send the dose data of these radiation workers to the dose registry after each monitoring period. In Armed Forces hospital, all radiation workers of the hospital receive TLD badges on quarterly basis from Defence Research Laboratory (DRL), Jodhpur, Rajasthan. If measured dose exceeds investigation level, accredited laboratory informs to AERB for further action. Subsequently AERB directs the institution to investigate possible causes of reported excessive exposure using questionnaires pertaining to individual work profile, type of procedure and workload in the reported period, availability of radiation protective accessories, procedure of handling of TLD badge. In case the reported dose is 100 mSv, the employer of the institute is directed to keep the radiation worker concerned away from radiation work till the investigations are completed satisfactorily. In addition the concerned radiation worker is called for Chromosome Aberration (CA) test at Radiological Physics & Advisory Division (RP & AD), BARC. In this study the overexposure cases reported from year 2006 to 2016 are presented. These cases relates to different X-ray modalities such as interventional Radiology, Radiography, Computed Tomography, Mammography, Nuclear Medicine and Cardiology.

Results and Discussion: From 2006-2016, four cases of overexposure were reported in the hospital. These cases pertained to Nuclear Medicine (02 in no.), Radiology (01 in no.) and Cardiology department (01 in no.). In all these overexposure cases after investigation it was found that all of them were non-genuine cases. The excessive exposure in these cases resulted due to improper handling and inappropriate storage of TLD badges, wrong placement of TLD badge while using (above lead apron) and unknown accidental exposure of TLD badge. In one case the worker (Equivalent Dose =301 mSv (G), 546 mSv (B)) left the badge in the radiation area. Hence the non- genuineness was quite obvious from the information obtained. In another case it was not traceable how badge get exposed as radiation worker (Dose =108.8 mSv) denied any misplacement of badge as well as undergoing any medical examination wearing the TLD badge. Subject was called for CA test at BARC also, but nothing came out of report. Last incidence (Dose = 14.85mSv) happened with a doctor (cardiologist) who placed TLD badge above lead apron during multiple procedures.

Conclusion: The non-genuine exposures are mainly due to carelessness in handling the badge (kept/dropped in radiation field), improper storage when the badge is not in use and negligence by radiation workers. To minimize the non-genuine cases of over exposure in medical X-ray facilities, proper training for the staff operating the x-ray equipment regarding proper use of TLD badge has been given.

   P-210: Introduction to Monte Carlo Simulation Through Microsoft Excel Top

A. K. Pandey

Department of Nuclear Medicine, All India Institute of Medical Sciences, New Delhi, India. E-mail: [email protected]

Introduction: The Monte Carlo technique has become ubiquitous in medical physics in the last 60 years. Monte Carlo techniques have played many roles in medical physics and its use is increasing day by day. The increased use of Monte Carlo techniques is partially due to the massive increases in computing power per unit cost and partially due to the increasing availability of many powerful software tools. The range of applications is very broad in medical physics, for example, there are commercial treatment planning systems for external beam radiotherapy which employ Monte Carlo techniques. Hence, it is important for young medical physicist to grasp the concept of Monte Carlo Simulation (MCS). There can be a variety of ways (as many ways as the number of instructors) “the concept of MCS” can be delivered to the students. Still, young medical physicist undergoing undergraduate and postgraduate courses often find difficult to grasp the concept of MCS.

Objectives: To introduce the concept of MCS through Microsoft Excel taking one example.

Materials and Methods: The Monte Carlo methodology for simulation, requires the following: (a) develop a complete definition of the problem, (b) determine the elements of the model that are uncertain and the nature of the uncertainty in terms of a probability distribution that represents its behavior, (c) implement the uncertain elements by using the RAND () or other Excel functions, (d) replicate a number of experiments sufficient in size to capture accurate behavior, (e) collect data from experiments, (f) analyze the result. The RAND ( ) function in Excel is used to perform sampling in MCS. The key characteristic of the RAND () is that each time it is used in a cell, it yields a random value which is independent of other cells containing the RAND () function. An interactive spreadsheet model for teaching introduction to MCS has been developed using Microsoft Excel under Microsoft windows operating system. This tool consists of the MCS of radionuclide decay and radiation detection. The tool will be used for illustration of the MCS concept during talk.

Results and Discussion: This tool is suitable for both students and teachers who are interested in the basic concepts of MCS in a simple manner. It offers ease of use and a shorter learning curve than theother method of illustrating the same concept (say: using computer programming languages). It is intended to complement rather than replace existing approaches to learning, such as lectures and assignments. The instructor can use them with some sort of projection facilities in lecture presentations for quick simulations and enhance the classroom environment. Students can use them as a self-studying framework to help them to grasp quickly.

   P-211: The Role of International Community in the Domestication of the Gains of Medical Physics Practices in the West African Sub-Region Top

Peter Ali, Kelechi Nwifior

Department of Physics, Ebonyi State College of Education, Ikwo, Ebonyi, Nigeria. E-mail: [email protected]

This paper is aimed at bringing to the limelight the current situation of medical physics practices in the West African sub region. Medical Physics in Africa has evolved over the last half a century from the Republic of South Africa in the southern tip of the continent to Ghana and Nigeria in the Western half and also Kenya, Uganda and United Republic of Tanzania in the Eastern sphere of the region and unto Algeria, Egypt, Morocco and Sudan in the Northern part. There is however a wide disparity in terms of educational infrastructure and availability of equipment across this very wide geographical landscape to provide the required medical physics services particularly in the health establishments as well as the other areas where the expertise of this cadre of professionals are needed. In terms of human resources capability, the continent can only boast of a slightly more than 300 personnel employed in and around her health facilities and about 60% of these staff are domiciled in just three countries – Egypt, Morocco and Republic of South Africa. The West African sub region has been noted to be still far behind in assessing the gains of medical physics practices. The learning objectives of the paper include identifying the medical physics infrastructure in terms of equipment and manpower, the status of education and training in the West African sub region, the gaps in the medical physics profession that should be addressed in the region, and the role expected of the international community.

   P-212: Status of Radiotherapy Treatment in Lebanon Top

Ibrahim Duhaini

Department of Radiation Oncology, Rafik Hariri University Hospital, Beirut, Lebanon. E-mail: [email protected]

Lebanon is located in the heart of the Middle East Region with a population of 4.5 million and is considered one of the best places of Medical Hot Spot destination that attracts many of the neighboring Arab countries to seek medical treatment. This is due to the fact of the highly skilled medical professionals and advanced health infrastructure in the country. Radiotherapy started in the early 70's with Cobalt Machines and has developed tremendously thought the years to include the highly technological and advanced Linac Systems. Now, there are 11 Hospitals that offer Radiotherapy Treatment with 17 Linacs equipped with the state of the art technology using 3-D Conformal, IMRT, Stereotactic Radiosurgery, IGRT and other modalities. In this presentation, an overview of the current cancer treatment in these 11 hospitals will be revealed. Detailed information will be unwrapped for the newly opened Radiotherapy Center at Nabih Berry Governmental University Hospital (NBGUH) in South Lebanon, which covers one third of the Lebanese population in that region. Also, detailed information will be exposed for the newly Upgraded Radiotherapy Department at Rafik Hariri University Hospital.

   P-213: The Effects of Electromagnetic Fields on Human Health Top

Ibrahim Duhaini

Department of Radiation Oncology, Rafik Hariri University Hospital, Beirut, Lebanon. E-mail: [email protected]

Since The beginning of the 20th century, we are overwhelmed by the increasing sources of the Electromagnetic Field (EMF) that is coming from telecommunication, electricity, appliances, medical equipment, and many other apparatus that we use in our daily life. Although these new technologies became inevitable and indispensable, the EMF they produce may cause health risks and hazards to human. Some studies show a link between exposure to EMF and increased rate of Leukemia, cancer, brain tumors and other health problems. Also, there is some uncertainty remains as to the actual mechanisms responsible for these biological hazards and which type of fields magnetic or electric or both are of great concern. It is needless to say that no matter the effects of these EMF be trivial or catastrophic, we should take all the necessary precautions to reduce our exposure to EMF as low as reasonably attainable. For this to occur, all those involved or affected by this exposure should follow the RF safety standards and guidelines set forth by the regulatory authorities like the IEEE, WHO, ICNIRP, and other likewise organizations. Any failure in taking immediate actions to the above guidelines, the public would be at a high epidemic risk of potentially fatal diseases in the future.

   P-214: Challenges Faced While Rolling Out E-Lora in an Armed Force Hospital Top

Kirti Tyagi1,2, Sachin Taneja1, Deboleena Mukherjee1,2, P. B. Mukherjee2

1Radiation Oncology Centre, INHS Asvini, 2Nuclear Medicine Centre, INHS Asvini, Colaba, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: In India Atomic Energy Regulatory Board (AERB) looks after the medical and industrial radiation facilities. All institutions dealing any type of equipments/units related to radiation have to be in sync with rules and regulations stipulated by AERB. Before 2014, dealings with AERB were done on hard copies, but after 2014 AERB aimed to become paperless and to improve transparency, AERB followed ONLINE wagon via e-Licensing of Radiation Applications (e-LORA) platform. This is a web based system which deals with regulatory processes associated with different practices using ionizing radiation in India.

Objective: We experienced few hiccups while carrying out the e-LORA drive in our hospital. In this paper we are summarizing how we tackled those challenges.

Materials and Methods: INHS Asvini is a super- specialty naval hospital, with 895 bed capacity. It has fully functional Radiotherapy, Nuclear medicine and Radiology departments. In 2013, AERB started e-LORA with radiotherapy first, then they opened up Diagnostic Radiology portal and later on Nuclear Medicine was also introduced. In AERB's e-LORA portal, medical facilities are divided into main categories (1) Radiotherapy, (2) Nuclear Medicine and (3) Diagnostic Radiology.

Result and Discussion: Radiotherapy: RT dept has a dual energy Linear accelerator and remote afterloading HDR brachytherapy unit. These machines have been installed after obtaining licenses from AERB. While transferring required data to e-LORA portal, a problem surfaced in arranging a computer with Internet access, scanner and printer attached to it. The computer at our electronic data processing centre came handy to us. Later on computers with internet access were made available to all heads of the departments. Small problems were encountered and debugged immediately. The transition to ONLINE for radiotherapy happened quite smoothly. Nuclear Medicine: This dept houses a SPECT, a PET-CT and it also has two bedded high dose radio Iodine ablation therapy ward. In Nuclear Medicine as our documentation was all up to the mark so no hindrance was there from shifting to e-LORA portal for obtaining NOC's. Diagnostic Radiology: Radiology department houses fixed and mobile radiography units, mammography unit, a CT scanner and an interventional DSA X-ray unit. The maximum work needed to be done during e-LORA was in Diagnostic Radiology as all X-ray units housed in a hospital were made to be registered under Diagnostic Radiology Portal. X- ray units with Dept of Radiology and Cardiology were all registered and licensed way before e-LORA. The main hindrance was the educational qualification of radiographers. In our naval institution the courses run by the institution are recognised by institutional academic body. This is due to different structure for fulfilling armed forces requirement. This part has been taken care as now radiographers course has been recognised by MUHS, Nashik. Other departments like Cardiology, Endocrinology, and Urology all were informed regarding e-LORA guidelines and regulations. These departments have started availing TLD services from Defence Lab, Jodhpur. The process of getting the layout plans of the rooms and performing quality assurance tests are all in progress.

Conclusion: It was a huge challenge in facilitating the transition of OFFLINE to ONLINE for becoming e-LORA competent. e-LORA has been introduced to all radiation related departments within the hospital. Updating all radiation workers on e-LORA is also a mammoth task, keeping in mind that all service personnel are bound to undergo transfers within a span of 3-5 years. Presently Nuclear Medicine, Radiology, Radiotherapy, Cardiology & RIA are harnessing benefits of this electronic licensing system.

   P-215: Brain Tumor Segmentation and Texture Analysis by Magnetic Resonance Imaging Top

Akbar Gharbali, Mir Hojjatollah Mousavi Maleki, Hossein Aghdasi1

Department of Medical Physics, Faculty of Medicine, Urmia University of Medical Science, 1Department of Medical Imaging Centre, Arefian Hospital, Urmia, Iran. E-mail: [email protected]

Introduction: Since the radiologist interpretation is often the clinicians guide for brain tumor treatment, differentiating malignancy from benign and detecting the tumor site and knowing its shape perfectly are important. So, automated brain image segmentation and texture analysis for determination precise form of the brain tumor and discrimination of benign and malignant brain tumors are critical to achieve the best results of treatment in comparison with radiologist visual texture analysis and or radiotherapist handy segmentation.

Objective: The goal of the present study is to explore detection and diagnostic potential of computer aided segmentation and texture analysis methods in precise determination of tumor shape and differentiation benign and malignant brain cancers by Magnetic Resonance Imaging (MRI).

Materials and Methods: In this study, the T2 weighted -MRI images of 50 patients with brain tumors were used. Firstly, the image segmentation was done by utilizing Mat lab software via Ant and Fuzzy clustering methods. Detection performance of the applied segmentation methods were evaluated by Dice Metric and ROC cure analysis. Secondly, the image texture analysis was done for differentiation of benign and malignant brain tumors by using the MaZda software via uploading two slice MRI- T2 weighted HASTE sequence images and up to 270 texture feature parameters were computed as a descriptor per ROI (Region of interest) per applied options. Then, extracted features parameters eliminated to 10 most effective texture feature parameters for describing texture patterns of the benign and malignant brain tumors. Optimal feature parameters were used for texture analysis by PCA (Principle component analysis), LDA (Linear discriminate analysis) with first nearest – neighbor (1- NN) classifier and NDA (Non-linear discriminate analysis) with Artificial neuralnetwork (A-NN) classifier. At the end, the discrimination performance of each of applied methods was evaluated by ROC cure analysis.

Results and Discussion: The better results of the segmentation phase were related to Ant algorithm with Dice Metric 85%, sensitivity of 89% and accuracy of 99%. In comparison with PCA and LDA, The best discrimination performance results for differentiation benign from malignant brain tumor was obtained by NDA analysis with sensitivity of 96% specificity 95% and accuracy of 95% respectively.

Conclusion: The results of this study show that the computerized segmentation and texture analysis of the brain tumor has potential to increase confidence of radiologist and radiotherapist in precisely segmenting and correctly discriminating brain tumors in Brain MRI.

   P-216: Investigate the Effect of Ionizing Irradiation on the Elasticity on Human Erythrocytes at Clinical Doses Top

E. Spyratou, M. Gazouli1, M. Dilvoi, M. Makropoulou2, A. Serafetinides2, E. P. Efstathopoulos, K. Platoni

2nd Department of Radiology, Medical School, National and Kapodistrian University of Athens, 1Department of Basic Medical Science, Laboratory of Biology, School of Medicine, University of Athens, 2Department of Physics, Faculty of Applied Mathematical and Physical Sciences, National Technical University of Athens, Zografou Campus, Athens, Greece. E-mail: [email protected]

Introduction: The biomechanical behavior of the erythrocyte's membrane skeleton is an important predictor of circulation efficiency and cell's health. The roughness of the cytoskeleton membrane is correlated with any redistribution of lipid molecules or proteins in the membrane bilayer and can indicate any rearrangement of the bilayer structure induced by external factors such as ionizing irradiation.

Objectives: In this work, we studied the effect of ionizing radiation on the morphology and the elastic properties of human erythrocytes after X-ray irradiation at clinical doses. The erythrocyte's changes were probing by using the advanced microscopic techniques of Atomic Force Microscopy and optical tweezers which is ideally suited for single cell measurements providing simultaneously information about the mechanical properties of the cells.

Materials and Methods: Whole human blood was drawn by venipuncture and subjected to the minimum possible treatment which can be induced morphological alterations. The blood samples were irradiated in the range of 0.2Gy -2.0 Gy doses and with a dose rate of 240 cGy/min. The morphology and the elastic modulus of the erythrocytes were examined in comparison with non-irradiated erythrocytes by using AFM and optical tweezers, and just few drops of whole blood without any special preparation.

Results and Discussion: No morphological changes appeared according to the shape of the erythrocytes. However, the roughness of the erythrocyte cytoskeleton was increased as the irradiation dose was increased according to AFM measurements. The elasticity modulus of the irradiated sample was reduced with the increasing of radiation dose. AFM and optical tweezers appears powerful nanotools and accurate techniques for probing the biomechanical properties of the erythrocytes. The elastic modulus and the membrane roughness of the erythrocytes could be an index to assess the damage caused by irradiation.

Acknowledgment: The authors would like to thank the “IKY fellowships of excellence for postgraduate studies in Greece”

   P-217: Biochemical Changes in Testes of Swiss Albina Mice Exposed to 2.45 GHz Microwaves Radiation Top

C. L. Jonwal1,2, Rashmi Sisodia1, V. K. Saxena3

Departments of 1Zoology and 3Physics, University of Rajasthan, Jaipur, Rajasthan, 2Department of Zoology, Hindu College, University of Delhi, Delhi, India. E-mail: [email protected]

Background: A number of studies have reported that male reproductive system is susceptible to electromagnetic fields (EMFs).

Objectives: The objectives of this study were to explore the changes in biochemical parameters of testes exposed to 2.45 GHz microwave radiations.

Materials and Methods: 6-8 weeks old male Swiss albino mice, weighing 35.0 ±3.0 grams were procured from inbred colony. Total 16 mice were divided into two groups; 1) Sham exposed, and 2) microwave exposed group. Microwave radiation experimental bench was used for the exposure to mice. Exposure was given in plexiglas cages. Mice were exposed to 2.45 GHz for 2 hrs/day for 30 days with power density 0.25 mW/cm2 and SAR 0.09 W/kg.

Results: Results revealed that 2.45 GHz radiations resulted in significant increase (P < 0.001) in catalase (CAT), malondialdehyde (MDA), reactive oxygen species (ROS) and decreased (P < 0.001) levels of glutathione peroxidase (GPx) and superoxide dismutase (SOD) (P < 0.05) in exposed group in comparison to control group.

Conclusion: We conclude that microwaves at 2.45 GHz frequency causes oxidative stress mediated cellular toxicity and it leads to adverse and detrimental biochemical changes in testis.

   P-218: The Effects of Co-60 Gamma Radiation on Human Lymphocytes by Micronuclei Assay Top

K. Mayakannan, S. K. Grace Mercy, V. Prabhakaran, C. S. Sureka

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: The study of radiation induced damage on chromosome is an essential part of genetic toxicology. The Cytokinesis-block micronucleus (CBMN) assay was well developed, radiation sensitive and widely used technique for assessing chromosome damage because they can measure both chromosome loss and breakage reliably. CBMN assay offer the various DNA damage analysis on genotoxicity and cytotoxicity such as chromosome rearrangement (nucleoplasmic bridges), cell division inhibition, necrosis and apoptosis.

Objective: To analyze the effects of Co-60 Gamma radiation induced DNA damage on human lymphocytes by Cytokinesis-block micronuclei assay.

Materials and Methods: The Peripheral blood was obtained in a 4 ml tube containing lithium heparin (BD Franklin Lakes NU USA). The blood was then divided into ten separate samples. The first sample was used as a control sample and other nine samples were irradiated with Co-60 Gamma irradiation dose of 0.5 Gy, 1 Gy, 2 Gy, 3 Gy, 4 Gy and 5 Gy. The blood samples were irradiated under Theratron 780c cobalt unit. The institutional human ethical committee of Bharathiar University approved all of the experimental procedure used in this study. After irradiation the cultures were set according to the most widely accepted method of French and Morley (1986), 5 ml of PB- Max Karyotyping medium (255703, Gibco,) and 0.5 ml of irradiated blood was added to the sterile 15 ml culture vial. All the procedure was carried out inside the Class-II Bio Safety Cabinet. Then the culture vial was placed inside the Co2 incubator with 37° C and 5% Co2 atmosphere. Cytochalasin B was added to the culture at a final concentration of 6 g/ml after 44 h to arrest cells at cytokinesis stage. At the end of incubation time (72 h), cells were harvested and supernatant were discarded by centrifugation and hypotonic solution (0.075M KCl) was added then left undisturbed for 20 minutes and supernatant were discarded by centrifugation. The cells were fixed in fresh fixative solution (methanol: acetic acid, 3:1) and this fixation step was repeated twice. About more than 200 cells were scored from each subject.

Results and Discussion: To find whether the micronuclei frequency followed poisson distribution the dispersion index σ2/y were calculated and it's close to 1 and indicated conformity with poisson distribution. Among the entire sample analyzed, the MN yield is found to be 1 for control sample, 5 at 0.5Gy, 14 at 1 Gy, 29 at 2 Gy, 37 at 3 Gy, 54 at 4 Gy and 90 at 5 Gy and data presented in [Table 1]. From the obtained result it is concluded that the yield of average micronuclei varied from 2-90 were found for doses ranging from 0-5Gy. As the dose increases, the micronuclei yield is also increased linearly. In-vitro irradiation of assay in Co60 beam at various dose levels. The induced cytokinesis blocked micronuclei are shown in [Figure 1].

   P-219: Enhancement of Radiation Effect by Cetuximab on Colon Cancer Cell Lines Top

Takamitsu Hara, Takeo Aoki, Yu Shinozaki, Hiro Sato1, Tomoo Funayama2, Tomoaki Tamaki3, Yoshiyuki Suzuki3, Atsushi Okazaki4, Takashi Nakano1

Department of Radiological Technology, School of Radiological Technology, Gunma Prefectural College of Health Sciences, 1Department of Radiation Oncology, Gunma University, 2Department of Radiation Applied Biology, Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology, Gunma, 3Department of Radiation Oncology, Fukushima Medical University, School of Medicine, Fukushima, 4Department of Radiation Oncology, Tsuboi Cancer Center Hospital, Koriyama, Japan. E-mail: [email protected]

Chemoradiotherapy is considered as an enhanced effective therapy on colon cancers. It has already been reported improved outcome by combination of cetuximab, a molecular EGFR-targeted drug, and radiotherapy which has synergistic effect in head and neck cancers. Therefore, we hypothesized that combination of cetuximab and radiotherapy on colon cancers would be an effective therapy. First, radiation sensitivities of 8 human colon cancer cell lines were examined by colony formation method. Next, radiosensitizing effect of cetuximab on each cell lines were examined by colony formation method. Radiosensitizing effect of cetuximab was observed in 3 of the 8 cell lines.

   P-220: Calculation of Attenuation Coefficients for Biological Substances at Various Gamma Energies Using the Geant4 Monte Carlo Code Top

C. S. Sureka, Francesco Longo1

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India, 2University of Trieste and INFN, Science Park Area, Padriciano, Trieste, Italy. E-mail: [email protected]

Introduction: The attenuation of gamma rays in tissues that are present between the organs of interest and the detector is one of the most important subjects in nuclear medicine and in radiation dosimetry as well. Hence, calculation of half-value thickness, linear, and mass attenuation coefficient of biological substances such as soft tissue, adipose tissue, compact bone, cortical bone, brain, lung, normal kidney, cancerous kidney, and water are important.

Objective: Calculate the half-value thickness, linear, and mass attenuation coefficient of different biological substances at various gamma ray energies using the Geant4 (Geomery and Tracking) Monte Carlo code.

Materials and Methods: The testem example of the Geant4 code was modified to study the attenuation of 122 (Co-57), 140 (Tc-99m), 356 (Ba-133), 364 (I-131), 662 (Cs-137), 893 keV (Na-22), and 1.25 MeV (Co-60) gamma rays through various biological substances such as soft tissue, adipose tissue, compact bone, cortical bone, brain, lung, normal kidney, cancerous kidney, and water of thickness ranging from 1 to 10 cm in 1 cm steps. The attenuating substance was constructed as a box defined by three parameters such as the material, thickness, and its transverse size of 10 cm. The standard EM physics was chosen to track 10 million gamma rays and its secondary particles. By knowing the number of gamma rays incident on the substance (I0), and transmitted (It) through the substance, a graph was drawn between the thickness of substance and ln (It/ I0). Then, the linear attenuation coefficient was calculated as it is the slope of the graph. The mass attenuation coefficient was calculated by dividing the linear attenuation coefficient by its density. Further, the thickness of the materials to transmit 50% of gamma rays (ie. half-value thickness) was calculated.

Results and Discussion: Calculated half-value thickness, linear, and mass attenuation coefficient of those biological substances at various gamma ray energies are reported and data presented in [Table 1],[Table 2],[Table 3] respectively. To validate the present results, the half value thickness, linear, and mass attenuation coefficient of water was compared with the calculated and measured data of published report. The calculated and measured half-value thickness of water at 662 keVis 8.095 cm and 9.096 cm +/- 0.291 respectively and it is comparable with the present value of 8.052 cm. The calculated and measured linear attenuation coefficient of water at 662 keV is0.085 cm-1 and 0.076+/- 0.002 respectively and it is also comparable with the present value of0.086 cm-1. The calculated and measured mass attenuation coefficient of water at 662 keV is0.0848 cm-1 and 0.0777+/- 0.002 respectively and it is also comparable with the present value of0.0861 cm-1. From this study, it is observed that the attenuation coefficients are different among biological substances due to the variation in its density and atomic composition. As the energy increases, the linear, and mass attenuation coefficient of these biological substances are decreased but its half-value thickness is increased significantly.
Table 1: Half-value thickness (cm) of various biological substances

Click here to view
Table 2: Linear attenuation coefficient of various biological substances

Click here to view
Table 3: Mass attenuation coefficient of various biological substances

Click here to view

   P-221: Estimation of Percentage Scattering Contribution in Activity Measurement of 60Co Teletherapy Sources Top

R. S. Vishwakarma, T. M. Ashraf1, S. A. Tariq1, S. P. Gupta1, P. Baral1, D. Paul1, T. Palani Selvam, L. N. Bandi2

Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, 2Board of Radiation and Isotope Technology, Navi Mumbai, Maharashtra, 1Regional Centre (RAPPCOF), Board of Radiation and Isotope Technology, Kota, Rajasthan, India. E-mail: [email protected]

Introduction: High intensity 60Co sources are used in various healthcares, agricultural and industrial applications. The 60Co activity in the form of slugs and capsules is recovered at Regional Centre, Kota of Board of Radiation and Isotope Technology (BRIT) from the various Pressurized Heavy Water Reactors in the country and sent for further processing to sealed sources fabrication facility. These sources are fabricated from 60Co pellets and slugs in shielded enclosure called as hot-cell.

Objective: The effect of scattered radiation during activity measurements in a hot-cell may lead to an over-estimation of the actual activity. In the present work, we have measured the scattering contribution from 60Co Teletherapy Sources produced in the hot-cell of Regional Centre-Kota of BRIT. The work also includes Monte Carlo-based calculations of scattering contribution.

Materials and Methods: The hot-cell has room dimensions of 2.4 m (length) x 2.4 m (width) x 4.8 m (height) with approximately 1.9 m thick high density reinforced cement concrete enclosure walls. The source strength measurements having nominal activities of 1 kCi - 10 kCi were carried out inside the hot-cell by using a 0.6 cm3 PTW-make ionization chamber which is calibrated at Secondary Standard Dosimetry Laboratory, BARC, Mumbai. The distance between source and ionization chamber is 2.575 m. Meter reading obtained by dosimeter system was corrected for temperature and pressure corrections and multiplied by air-kerma calibration coefficient, Nk,air. Using conversion factors and correcting for distance, the source strength is measured in unit of roentgen per minute at 1 meter (RMM). The measured RMM values include contributions from primary radiation from the source and scattered radiation from walls, floor, ceiling and other objects present in the hot-cell. The measurements of scatter contribution are carried out by blocking the primary radiation beam by a truncated conical lead block of 30 cm height without altering the source-detector geometry. The scattering contribution was calculated from ratio of measured RMM with and without lead cone. RMM values were also calculated using the MCNP (version 3.1) Monte Carlo code by modeling the experimental setup. Photon fluence spectrum was scored which was converted to Roentgen per initial photon (R/photon) by using the mass-energy-absorption coefficients of air2.

Results and Discussion: The measured and Monte Carlo-based estimated percentage scattering contributions are about 12% and 13%, respectively. Measurement was also carried by removing the transport flask present inside the hot cell. Such measurement did not change the scatter contribution which suggests that the structural materials around the source contribute to the scatter. The investigation concludes that there is an improvement in the RMM value by about 12% while accounting for scatter contribution.

   P-222: Detection Of Minerals Using Sem-Edx in Same Family Medicinal Plant Leaves Top

Santoshkumar S. Teerthe, A. Ashwini, B. R. Kerur, S. Narayana Kalkura1

Department of Physics, Gulbarga University, Gulbarga, Karnataka, 1Crystal Growth Centre, Anna University, Chennai, Tamil Nadu, India. E-mail: [email protected]

Natural plants have been used as potential source of therapeutic medicine, home remedies and also primary health care throughout the history. Medicinal plants are considered safe for human health, it is known that certain organic and inorganic elements or metals played important role in plants as well as human body for secondary metabolites. Elements or metals were uptake from soil to roots, from environment dry deposition or by contamination during processing. Plant materials may contain high major/minor and trace amounts of essential elements along with high content of elements which are exceeds the permissible limits of intake. The essential elements such as Magnesium, Aluminum, calcium, phosphorous, vanadium, chromium, nickel, Iron, copper, zinc, Arsenic, Cadmium, molybdenum, antimony, mercury, Lead etc. The World Health Organization (WHO) has established maximum concentration limits for these elements in order to ensure the safe consumption and use of herbal medicinal plants. Therefore, it is important to determine the concentrations of these elements in different parts of herbal medicinal plants. In present research work two different families viz., Apocynaceae and Myrtaceae herbal medicinal plants samples were collected from Yadgir district of North-East Karnataka region. The study of structural morphology and detection of elemental concentration were carried out by using SEM-EDX method. The elements likes C, O, Mg, Si, S, Cl, K, Ca, Mn, Fe, are found in effective concentrations and the crystalline and cylindrical shaped election image impact within 20μm and the value of elements Na, Al, Cu, Zn, Br and As were found in 1wt% of concentration. The quantitative elemental concentration analysis was identified with x-ray energy which is observed in between 1 KeV to 16 KeV. Further the present investigation suggests that the collected herbal medicinal plants have good alignments of secondary metabolites, functional groups and trace elements. The present data gives good information on antioxidant, anti informant and Physiochemical study, and useful for treatment and preparation of new herbal medicinal drugs for Cancer, HIV-AIDS, Diabetes, brain tumor etc. The given [Table 1] and [Table 2] presents the percentage variations of elemental content in different plant and the study of morphology surface structure with energy- spectra.
Table 1: Details of elemental concentration analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy method in (wt%)

Click here to view
Table 2: Structural morphology, energy spectra and quantitative analysis

Click here to view

   P-223: Investigation of Mass Attenuation Coefficients of Dosimetric Materials Using Fluka Monte Carlo Code Top

Amandeep Sharma, Bhajan Singh1, B. S. Sandhu1

Department of Physics, Akal University, Talwandi Sabo, 1Department of Physics, Punjabi University, Patiala, Punjab, India. E-mail: [email protected]

Introduction: The use of radiation in health physics, medical physics, radiation dosimetry, radiation protection and radiobiology require knowledge of radiation interaction with the materials for shielding and dose measurement. When a beam of X or gamma rays pass through matter, the removal of photons from the beam is called attenuation. The linear attenuation coefficient is defined as the fraction of photons removed from a monoenergetic beam of X or gamma rays per unit thickness of material. The simulation to estimate the mass attenuation coefficient can be done with the use of well-known simulation program such as FLUKA. This tool is based on the Monte Carlo (MC) methods to simulate the interaction of particles with their traversing medium. In medical imaging, such as PET, an attenuation correction for gamma photons is fulfilled to enhance the spatial resolution, i.e., image quality. This correction is performed by taking into consideration the mass attenuation coefficients of the related parts of the human body. In this regard, mass attenuation coefficients of the related biological materials have great importance in this process. For this reason, MC method (FLUKA) was utilized to determine the coefficients for some dosimetric material and obtained results are compared with the WinXCom.

Objectives: (i) Introduction to FLUKA Monte Carlo code for the beginners

  1. Application of FLUKA code to calculate essential parameter, mass attenuation coefficient, for medical physics

Materials and Methods: In this work, we have estimated the mass attenuation coefficients of some dosimetric materials like LiF, CaCO3, CdSO4, BaSO4, water (H2O), ethylene (C2H4), bakelite (C9H9O) and PMMA etc. for the photons with energy of 661.6 keV by using the FLUKA Monte Carlo code due to its event-by-event tracking feature. The applications of dosimetric materials in radiation physics and radiobiology are essential for exposure monitoring and estimation of the dose. FLUKA input data cards have been arranged in sequential order. A simple cylindrical geometry with the axis along the z-direction was described in the input file. A beam of 1x105 gamma-rays was directed towards the materials in the z-direction and attenuated in cylindrical samples. The results of photon transmission were obtained from output files for each of the material thicknesses using the USRBDX score card. By plotting ln(Io/I) versus thickness, the slope was calculated. The linear attenuation coefficients were calculated by using Lambert-Beer's law.

Results and Discussion: Monte Carlo simulation is a powerful tool for studying the interaction of photons in any material. The mass attenuation coefficient, an essential parameter, of some dosimetric materials with potential applications in dosimery, medical and radiation protection have been investigated using the FLUKA Monte Carlo simulation code. The special feature of FLUKA, probably not found in any other Monte Carlo program, is its double capability to be used in a biased mode as well as fully analogue code. The simulated results, for attenuation coefficient of dosimetric material/ biological substitutes, obtained by FLUKA agree well with WinXCom prediction. It is observed that the mass attenuation coefficients of the selected dosimetric materials are small when low atomic number elements are predominant, whereas large for high atomic number elements. The results of this preliminary study demonstrate that FLUKA Monte Carlo simulations can be applied to estimate mass attenuation coefficients for various attenuators and energies especially when it is hard to set up an experiment.

   P-224: Radiation Oncology Facilities: Current Status and Future Perspectives in the Countries Members of the Mefomp Top

Rabih Hammoud, Tarraf Torfeh, Satheesh Paloor, Noora Al-Hammadi

Department of Radiation Oncology, National Center for Cancer Care and Research, Hamad Medical Corporation, Doha, Qatar. E-mail: [email protected]

Introduction: As a part of the International Organization for Medical Physics (IOMP), the Middle East Federation of Medical Physics (MEFOMP) is a regional organisation that includes the medical physics societies and associations of the following countries: Bahrain, Iraq, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, Syria, United Arab Emirates and Yemen. The socio-economic and political factors are known to influence healthcare facilities in general and radiation oncology in particular. In view of the different socio-economic and political status in these countries, the aim of this work is to share the current status of the Radiation Oncology resources in these countries.

Materials and Methods: A detailed description of the current status of the radiation oncology facilities will be presented for each country. Furthermore, some of the state of the art projects will be highlighted and discussed such as the implementation of proton radiation therapy. The latest advancement in the sate of Qatar as well as an overview of the future perspectives in the radiation oncology facilities will also be presented. This study will cover all the areas of the radiation oncology including the simulation, treatment planning, the delivery and the personnel with an emphasis on some of the projects such as MR guided Brachytherapy and CyberKnife.

Results: The diversity of the socio-economical and political status in the countries that are members of the MEFOMP resulted in a wide range of technological advancement in the radiation oncology facilities and resources. Ranging from primitive facilities with low qualified staff observed in the some countries to a very advanced technology and qualified personnel in other countries.

Discussion: This study allowed having an overview of the current and future status of the development in the radiation oncology in the countries members of the MEFOMP. This study allowed also identifying the areas of weakness and strength in the radiation oncology for each country which represents an important step for identifying development and improvement areas.

   P-225: Association of Proton Pump Inhibitors with Hypomagnesemia: A Cross Sectional Study at a Tertiary Health Care Centre Top

Sejal Sejwani, Pramod Jha, Garvit Garg, Ronak Shah1

Department of Medicine, 1Department of PSM, Dhiraj Hospital, Sumandeep Vidyapeeth, Baroda, Gujarat, India. E-mail: [email protected]

Introduction: Proton Pump Inhibitors (PPIs) are one of the most common class of drugs that are used in almost all alternative prescription. Few studies have shown that PPIs are responsible for hypomagnesemia.

Aim and Objective: To analyse whether prolonged use of Proton Pump Inhibitor is associated with hypomagnesmia.

Methodology: It is a cross sectional, single centred study of 3 months duration, at a tertiary health centre in Baroda. 80 patients were enrolled in the study with non critical illness and divided them in two arms viz 'PPI group' (n=40) and 'non PPI' group (n=40). Patients with history of PPI consumption of 3 months or more duration were enrolled in 'PPI group' while patients with no history of PPI use in last 3 months were in 'non PPI group'. Serum Magnesium (S. Mg) levels were estimated and data was collected and analysed.

Outcome: This study revealed that mean S. Mg in PPI group was 1.69 mg/dL while in non PPI users mean S. Mg was 1.93 mg/dL, the difference being statistically significant (p = 0.00). However, female PPI users had slightly lower S. Mg levels in comparison to male PPI users. S.Mg levels were analysed in age groups also which revealed lower S. Mg in PPI users patients with age above 40 years i.e 1.65 mg/dL while slightly higher in patients below 40years of age. Also duration of PPI was analysed which showed low level of S.Mg in patients with PPI use of more than 7months. Analysis of pantoprazole, rabeprazole and omeprazole depicted that pantoprazole users had less S.Mg levels as compared to other two drugs.

Conclusion: This study revealed that S.Mg levels were low in PPI users. To avoid fatal complications of hypomagnesemia rational use of PPI should be done specially in elderly group.

   p-226: Development of Green LEDs based Optical Bleaching Setup for Thermoluminescence dosimetry application Top

Mukesh Uke, L. Paliwal, S. Kadam, A. K. Singh, D. K. Koul, D. Datta

Division of Radiological Physics and Advisory, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]

Introduction: CaSO4: Dy based thermoluminescence dosimetry programme is being used in the country wide personnel monitoring program in India. The TL glow curve of CaSO4: Dy consists of a dosimetric peak at 220oC and a low temperature peak at 120oC, which is unstable at room temperature. The TL integral counts reduces by 15% in 7 days after irradiation due to the thermal fading of 120oC TL peak at room temperature. So, if TLD cards are processed immediately after the exposure the conventional dose evaluation protocol will yield un-reliable results due to presence of low temperature peak at 120oC. In order to overcome this difficulty an alternative technique based on optical bleaching was developed for the urgent processing of TLD cards. Optical bleaching with green LED (555 nm photons) was observed to remove the low temperature TL peak without affecting the dosimetric peak.[1] This setup has the facility of selecting the desired intensity and time period of bleaching.

Experimental Method: The bleaching setup consists of 3023 Buck Puck LED power module, green high power LEDs, glass sheet, rotary switch, etc. A 3023 module is a current regulated driver for powering LEDs with high efficiency. A rotary switch is used in 5 modes of intensity control of the green LEDs string. The light intensity of LEDs is ~25000 lux which is measured by light meter (LX-101A). TLD cards were prepared using personnel monitoring discs of CaSO4:Dy. These cards were annealed and sensitivity variations within 6% were selected for the experiment. Three sets of TLD badges were exposed to various fractionated doses on different days. Each TLD cards were bleached for 1 hr 30 minutes having an intensity of 25000 lux at the sample position before TL readout. The TL was recorded in semi automatic TLD badge reader.

Results and Discussions: The CaSO4: Dy based discs (5 mm Dia.) were exposed to 20mSv and kept at the centre on the bleaching glass plate. These were bleached for 1 hr 30 minutes and TL readings were taken in semi automatic TLD badge reader. Peak intensities of dosimetric peaks were compared. The variation was found to be within 6%. [Figure 1] shows that the low temperature TL peak which is responsible for fading is bleached out. Doses were estimated immediately after the last irradiation and compared with actual delivered dose. The dose delivered and dose estimated in this study are compared in [Table 1].
Table 1: Comparison of dose delivered to CaSO4: Dy TLD and dose evaluated

Click here to view

Conclusion: The results shows that optical bleaching technique makes it possible to evaluate dose immediately after exposure. This might be a requirement for urgent dose evaluation in case of personnel monitoring using CaSO4: Dy TLDs. This setup has been working satisfactorily for the last one year in RPAD, BARC, CT&CRS, Anushaktinagar, Mumbai.

   P-227: Indigenous Technology for Radioactivity Measurement in Foodstuff and Drinks Top

P. Narayan, R. M. Sahani, S. L. Damor, G. L. Baheti

Defence Laboratory, DRDO, Jodhpur, Rajasthan, India. E-mail: [email protected]

Natural radioactivity concentration in food items has been reported internationally in the range of 40-600 Bq/kg with 40K as major isotope with typical activity 50, 420, 165, and 125 Bq/kg in milk, milk powder, potato and beef respectively. Due to variation in radiotoxicity, IAEA has stipulated different consumption limit for different radioisotopes (134Cs, 137Cs, 103Ru, 106Ru, and 89Sr) produced during nuclear detonation and accident. This is the reason to have dedicated technology for rapid radioactivity measurement and identification of isotopes presence in foodstuff and drinks for controlling internal exposure especially during nuclear emergency. An indigenous technology for radioactivity measurement in edible items has been developed using NaI (Tl) gamma detector (Size:75 mm x 75 mm). It is based on the detection of gamma rays emitted from the materials under investigation through conversion of scintillation light into electrical signal. The electrical signal is fed to 1k Multichannel Analyzer (MCA) for its further processing and identifying the type and level of contamination in the sample under examination. The system compares the sample count data with natural background and generates the visual warning and subsequently computes the activity concentration. The system has been facilitated with three size sample containers (100, 500 and 1000 ml) for accommodating radioactive samples of wide activity range. It is provided with adequate radiation shielding (30 lead) for reducing unwanted signal due to cosmogenic and terrestrial radiation, which helps in reducing MDA (minimum detection activity) in high radiation background area. The system has capability for correcting the signal loss due to self-attenuation of radiation through the sample under measurement depending upon its matrix and density. The system has three point energy calibration facility using standard reference sources. The system was subjected to various radiological and physical quality tests and the results found to be in agreement with the internationally available technology. At typical PMT settings (HV: 750 V and Gain: 15%), there has been linear relationship between energy (60 to 1460 keV) and channel number within 0.1% with calibration factor 2.37 keV/channel. The system efficiency has been found to vary inversely with the photon energy, which decreases from 17% to 2% with increase in the energy from 80 keV to 1.46 MeV. It gives reproducible results within ±2.5% with measurement repeatability ±2%. It can measure radioactivity concentration in food samples within activity range 50 to 106 Bq/kg in 60s data acquisition time. This development is “First of its kind” in India, which utilizes raw food samples and drinks for radioactivity measurement. It generates visual warnings (Green, Yellow & Red) depending upon the level of radioactivity presence in the item under investigation. It identifies the radioisotope/s and computes gross as well as individual isotope activity. At a time it can identify 10 radioisotopes and compute their respective activity concentration. The system finally generates sample contamination analysis report and save it for future record and application. This technology is useful for military, civilian and research applications involving low level radioactivity measurement in any types of samples restricted with density up to 3 g/cc. The equipment may be helpful in controlling the radioactivity spread and restricting the contaminated food consumption. This paper reports the scientific and technical work carried out for development of the indigenous technology for food radioactivity measurement.

   P-228: Estimation of Mid Point Dose for Cancer Cervix Patients Using Epid Based In Vivo Dosimetry Top

B. Gowri1,2, C. Anu Radha1, V. Ramasubramanian1, N. Surendran2, A. Gopiraj2

1School of Advanced Sciences, VIT University, Vellore, 2Department of Medical Physics, Government Arignar Anna Memorial Cancer Hospital and Research Institute, RCC, Kanchipuram, Tamil Nadu, India. E-mail: [email protected]

Aim: To estimate the midpoint dose delivered to cancer cervix patients treated by conventional technique using Electronic Portal Imaging Device (EPID) based in vivo dosimetry.

Materials and Methods: Clinac 2100C equipped with aS500 EPID was used in this study. Phantom study was carried out using 0.6 cc chamber to establish a relationship between the EPID measured CU values and ion chamber measured midpoint dose in Gy. A Gy/CU look up table was generated and was used in the estimation of midpoint dose of patients. The look up table was validated using phantom for rectangular fields and for different separations. 25 patients of cancer cervix was included in this study and the delivered dose to the midpoint of the patients was estimated using EPID. The deviation between the prescribed and the measured dose was calculated and analysed.

Results and Discussion: EPID showed a linear response with increase in Monitor unit. The validation of the Gy/CU table for rectangular fields and other than measured separation showed minimal deviation in the range of 0.00 to 0.40 % for equivalent field sizes from 6.85 cm2 to 16.94 cm2 and from 0.12 to 0.24 % for 15.0 cm separation. 250 fields were measured for 25 patients, 10 measurements per patient, weekly once and for 5 weeks. The results show that out of 250 measurements, 98% of the measurements are within ±5% and 83.2% are within ±3% of the prescribed dose with a standard deviation of 1.66%.

Conclusion: EPID can be effectively used as an in vivo dosimeter for any busy radiotherapy department with minimal effort, time and without any inconvenience to the patients unlike other in vivo dosimeters.

   P-229: Comparing and Evaluating the Post Irradiated EBT-3 Gafchromic Flim Using Commercial Flatbed Scanner and Densoquick 2 Densitometer Top

S. Nilavarasu, G. Bharanidharan, P. Aruna, J. Velmurugan, P. Thamilkumar1, R. R. Rai1, S. Ganesan

Department of Medical Physics, Anna University, 1Department of Radiotherapy, Dr. Rai Memorial Cancer Institute, Chennai, Tamil Nadu, India. E-mail: [email protected]

Introduction: The emerging technologies in the field of radiotherapy increase the planning and delivery complexities hence, there is need for entire verification of treatment. Due to the sharp dose gradient around the normal critical structures which enhances the volume effect for almost all the detectors and due to the low energy contribution to the absorbed dose, there is difficulty in dose measurement hence, Radiochromic film is appropriate for entire dose verification due to its high spatial resolution, tissue equivalency and low energy dependence. Recently gafchromic EBT3 film is independent of inhomogines dose response post irradiation colouration and low sensitivity. There are several types of densitometer in use for 2D film dosimetry and each of them has its own specific characteristics. The aim of the current study is examine the characteristics of EPSON Expression 11000XL and Densoquick 2 densitometer in combination with gafchromic EBT3 film and to compare the results between the two densitometers.

Materials and Methods: To examine the characteristics of EPSON Expression 11000XL (EPSON-Japan) and Densoquick 2 densitometer (PTW- Germany). Gafchromic EBT3 film were used after irradiating in Varian LINAC true beam Long stand with 6MV and 10MV without FFF.

Result and Discussion: All the films were scanned before irradiation in order to subtract the OD of unirradiated film from irradiated film. Gafchromic EBT3 film was irradiated for various field sizes such as 2x2 cm2, 3x3 cm2, 5x5 cm2 , 10x10 cm2, 15x15 cm2, 20x20 cm2 with various dose rates ranging from 200 to 600 MU/minute for 6MV and 10MV photon beam without FFF. The irradiated film were measured for the absorbed dose after 24 hours and scanned using a commercially available EPSON Expression 11000XL flat bed scanner and optical densities for various filed sizes and dose rates were calculated using verisoft software and the OD were also calculated using desoquick2 densitometer manually at various points in the central axis towards the off-axis of the field size. The absorbed Optical density shows that densoquick 2 is more accurate than commercially available flatbed scanner, Since the optical density observed in EPSON Expression 11000XL shows fluctuation initially due to the warm up of the lamp of the scanner later after performing more than two or three scans. The optical density observed in the flat bed scanner is comparable with densoquick2 densitometer which was within ±5%.

Conclusion: Both densoquick2 densitometer and EPSON Expression 11000XL densitometer is an excellent device to perform accurate two dimensional film dosimetry with gafchromic EBT3 However, some precautions and corrections have to be carried out in the flat bed scanner which needs to be taken in to account with the result. In case of densoquick2 although it was accurate than flat bed scanner the processing time required to get the result is more and tedious because everything need to be done manually henceforth from the results, it is concluded that both the devices can be used to perform accurate two dimensional film dosimetry.

   P-230: Utilization of Osld as the Quality Control Indicator for In-Vivo Measurements in Total Body Irradiation Top

V. Karthik, Salih Osman, Sandeep Singh, Kanan Jassal, Biplab Sarkar, T. Ganesh, Upendra Kumar Giri

Department of Radiation Oncology, Fortis Memorial Research Institute, Gurgaon, Haryana, India. E-mail: [email protected]

Objective: The In vivo dosimetry involves a measurement of the dose delivered to the patient in the treatment conditions to detect a possible deviation between the prescribed and the delivered dose. The advent of the optically stimulated luminescence dosimeters (OSLD), particularly in the Nano Dots form, is a very appropriate tool for its size, ease of handling, accurate and fast reading. This study investigate the application of OSLD for the quality control of Total Body Irradiation (TBI) treatment.

Introduction: Special techniques of radiation treatments generally require a quality control very thorough because in general tend to be high risk techniques of complications due to imparting high doses in a small volume or involve a very large volume of the patient are the techniques of TBI either photons or electrons. In these techniques a moderate error in the given dose can mean a very significant variation in tumor control probability (TCP) or the likelihood of complications in normal tissues has happened in known published accidents and can be deduced from the typical sigmoid curve of response vs. dose. The technique in vivo dosimetry has proved useful a final tool to detect any possible error in the chain of procedures to which is subjected prior to radiation treatment. This study evaluate the feasibility of OSLD for in-vivo dosimetry of patients undergoing TBI.

Materials and Methods: In-vivo dose measurements using OSLD nanoDots (LANDAUER, Glenwood, Illinois) were done in a total of 24 patients who treated with 6 MV & 15 MV. To provide a uniform dose to the entire patient length, the treatment was split into 2 lateral fields. In this technique, the patient is kept inside the TBI box which is filled with rice filled muslin bags and irradiated using bilateral parallel opposed beams of 40×40 cm2 size with 45° collimator rotation at an SSD of 333.5 cm in an Elekta Synergy Platform linear accelerator (Elekta AB, Stockholm, Sweden). All patients received a dose of 2 Gy in single fraction as conditioning regimen. The beams were equally weighted at the centre of the box which lies exactly at mid-line plane of the patient. The nanoDots were placed at both medially and laterally including forehead, right and left neck, right and left lung, umbilicus, right and left abdomen, upper right of thigh, and right knee.

Results: Measurement values of doses with nanoDots were found for medial sites forehead, umbilicus, and knee were, 2.19±9.66, 2.12±6.35, 2.16±8.1 Grey respectively. Lateral sites right and left neck, right and left lung, right and left abdomen were 2.17±8.75, 2.12±6.37, 2.15±7.81, 2.16±8.42, 2.21±5.35, and 2.17±8.66 Grey respectively. For medially placed nanoDots measurement Dmean was 2.16±9.66 Grey and laterally Dmean was 2.16±8.75 Grey.

Discussion: The characterization of the nanoDots dosimeters in terms of dose response, dose rate, angulation and other parameters in measuring conditions is the essential step before beginning the ultimate goal. The nanoDots showed their capacity for use invivo dosimetry, after tests on phantoms for both characterization and for treatment simulation. Finally, in clinical practice results in the three irradiation techniques raised they showed highly satisfactory results with acceptable deviations and comparable with existing previous techniques, proving the feasibility of conducting invivo dosimetry with OSL easily and efficiently.

Conclusion: The results demonstrate that nanoDot can be potentially used for TBI verification in various levels on Patients body, with a high degree of accuracy and precision. In addition OSLD exhibit better dose reproducibility with standard deviation of 0.6%. The dose response was also linear for both medial and lateral fields. This can help with time saving and work efficiency in the clinic.

   P-231: Dosimetric Effect of Brass Mesh Bolus on Surface Dose Distributions Top

Zakiya S. Al-Rahbi1,2, Dean L. Cutajar1,3, Peter Metcalfe1, Anatoly B. Rosenfeld1

1Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 3St. George Cancer Care Centre, St. George Hospital, Kogarah, Australia, 2Department of Radiotherapy, National Oncology Center, The Royal Hospital, Muscat, Oman. E-mail: [email protected]

Purpose: To investigate the feasibility of using the Brass Mesh Bolus as an alternative to tissue-equivalent Bolus for post mastectomy chest wall cancer by characterizing the spatial distribution (beam profile) using 2-mm fine Brass Mesh Bolus during chest wall PMRT.

Materials and Methods: Transmission surface dose data were acquired for a 6 MV photon beam in a solid water phantom using MOSkin TM dosimeter. Data were measured under the case of: full hole Face-up Brass, empty hole Face-up Brass Bolus, full hole Face-down Brass and empty hole Brass Bolus. The same steps were done to measure the exit dose.

Gafchromic EBT3 film strips were used to plot dose profile at surface and 10 cm depth for Face-up Brass, Face-down Brass, double brass, 0.5 cm and 1.0 cm of Superflab TE bolus.

Results: Generally, the Face-up Brass Bolus produced more surface dose than the Face-down Brass Bolus. The enhanced dose to the skin at the skin-mesh interface is due primarily to secondary charged particles produced in the mesh Brass.

The surface dose measured via MOSkin TM dosimeter increased from 19.2 ± 1.0% to 63.1± 2.1% under full hole Face-up Brass, 51.2 ± 1.2% under empty hole Face-up Brass, 61.5 ± 0.5% under full hole Face-down Brass Bolus, and 41.3 ± 2.1% under empty hole Face-down Brass Bolus.

The percentage difference in the dose measured under full holes between face-up versus Face-down Brass was less than 2% for entrance dose and 10% for exit dose, whereas the percentage difference under empty holes was approximately 3% for entrance dose and about 5% for the exit dose.

For Face-up Brass Bolus, the dose measured under full holes versus empty holes was around 12%, whereas it was 20% for Face-down Brass Bolus. For exit dose, the dose measured under full holes versus empty holes was around 2% and 10% for Face-up and Face-down Brass Bolus, respectively.

Gafchromic EBT3 film strip measurements show that the mesh bolus produced ripple beam profiles and these oscillations are expected due to the mesh brass construction which results in inhomogeneous attenuation. The profiles for Face-up Brass Bolus oscillated from -58.8% to 48.8% and 61.6% - 50.3% under empty and full holes, respectively. For Face-down Brass Bolus, the profiles fluctuated from 56.3% to 41.5% under empty holes and from 59.3% to 43.3% under full holes.

Conclusions: Face-up Brass mesh has been successfully introduced into clinical practice in several institutions as an alternative to tissue-equivalent bolus, although usually for a percentage of treatment fractions. However, the effect of the mesh on surface and superficial dose when used in conjunction with tangential irradiation geometries is complicated and requires careful consideration before clinical use.

   P-232: Comparison of Ito, Fto and Gold Coated Cathode of the Pcb Technology Based 3D Positive Ion Detector Top

P. Venkatraman, C. S. Sureka

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: Nanodosimetry is a natural extension of microdosimetry, developed by H.H. Rossi and his colleagues more than 40 years ago, into the nanometer domain. Many of the concepts that were originally developed for micro dosimetry have been applied directly to nanodosimetry. One of these concepts is that, the geometrically well-defined regions in which the energy absorbed or the number of energy transfers is studied. There is a growing interest to study the interaction of ionizing radiation with matter/gas at nanometer level as it simulates the damage on DNA. Further in the field of nanodosimetry, the appropriate selection of cathode materials of its sensitive detector plays a more significant role in order to improve the performance of the detector.

Objective: To compare the Indium Tin Oxide (ITO), Fluorine Tin Oxide (FTO) and Gold coated cathode materials of the PCB technology based detector in order to optimize the cathode of the detector.

Materials and Methods: To find the suitable cathode material of the newly fabricated PCB technology based detector, the signal captures using three different cathode coated materials such as Indium Tin Oxide (ITO), Fluorine Tin Oxide (FTO) of 7 ohm resistivity, and gold of 0.1 ohm resistivity were studied as conducting layer over the ceramic insulator using Co-60 source under methane medium at an applied cathode voltage of -470 V. Further, variations in amplitude and efficiency of those signals at various pressure ranging from 0-10 Torr were analyzed.

Result and Discussion: It is observed that the signal amplitude and efficiency were found to be 785% and 67.27%, and 646% and 15.48% higher for gold than ITO, FTO and gold respectively. From this data, it is inferred that gold coated cathode showed better performance than ITO and FTO coated cathode. This may be due to the fact that the mobility of electrons in gold is higher than ITO and FTO materials. Further, it is observed that the signal efficiency gets decreased when the pressure is increased and its amplitude is almost constant throughout the range of pressure for all the materials. From these results, it is concluded that the gold coated cathode can improve the performance of the PCB technology based 3D positive ion detector.

   P-233: AN In-Vitro Study of Breast Cancer Diagnosis at all Stages Using the PCB Technology Based Nanodosimeter Top

P. Venkatraman, C. S. Sureka

Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction : In the modern field of nanodosimetry, the Printed Circuit Board (PCB) technology based positive ion detector has been identified as a device to detect cancer at all stages. The specific volatile organic compounds (VOCs) such as alkanes, alkenes, ketones, halogenated hydrocarbons, aldehydes, alcohols, esters, unsaturated hydrocarbons, terpenes, siloxanes, and aromates exhaled by breast cancer cells in the nano environment are the source biomarkers of to diagnose breast cancer. It also serves as direct evidence that the diagnosis of breast cancer through exhaled air without disturbing the patient is possible. Objective: The objective of the present paper is to analyse the normal and breast cancer tissues of all stages using the Nanodosimeter in order to confirm the suitability of this technique for breast cancer detection.

Materials and Methods: Multilayer PCB technology based Nanodosimeter was designed to capture positive ions produced by the interaction of ionizing radiation with low pressure gas medium. In order to confirm the signal, the present signal captured under methane and nitrogen medium at 1 to 10 Torr pressure was compared with the signal published by M. Casiraghi et al (Radiation protection dosimetry, 2015). After the validation, the normal breast tissues were placed inside the chamber and it was evacuated in order to remove all molecules present in the chamber. Then, it is allowed to exhale molecules at various pressures in order to measure the amplitude, rise time, fall time, and number of pulses of the signal. Later, these normal tissues were replaced with breast cancer tissues of all stages (Stage 0, 1, 2, 3a, 3b, and 4) in the evacuated medium and the same was allowed to exhale Volatile Organic Compounds (VOCs) to capture signal at various pressure ranging from 1 to 10 Torr. Those signals were captured for 5 sets of both normal and cancerous tissues at each stage.

Results and Discussion: When comparing the present signal with published signal under methane and nitrogen medium, it is confirmed that the present detector is well suited with higher efficiency to proceed further. When comparing the signal captured for both normal and breast cancer tissues, it is observed that the signals of normal and cancerous breast tissues gets varied in terms of amplitude, rise time, fall time, and number of pulses at all pressures and it showed maximum strength at 1 Torr pressure. It is observed that the signal amplitude, rise time, fall time and number of pulses of normal breast tissues was found to be 74.1±0.08 Volts, 2.4±0.005 ms, 480±0.0 μs, and 581±40.5 respectively. The signal amplitude, rise time, fall time and number of pulses at Stage 0, 1, 2, 3a, 3b, and 4 of breast cancer tissues are 76.8±0.28 Volts, 1.6±0.005 ms, 460 ± 0.02 μs and 1008±231.125; 79.3±0.15 Volts, 1.8±0.001 ms, 450 ±0.025 μs and 1546±364.5; 86.3 ±0.01 Volts, 480±0.0 μs, 480±0.0 μs and 2596±420.5; 88.5±0.03 Volts, 2.1±0.005 ms, 480±0.0 μs, and 3434±200; 90.7±0.01 Volts, 1.9±0.012 ms, 480±0.0 μs, and 3795±2.53; and 91.5±0.03 Volts, 470±0.2 μs, 480±0.0 μs, and 4077±210.12 respectively. From this data, it is inferred that the amplitude, rise time and number of pulses are gradually increased when the tissue became cancer and developed into various stages. Based on these, it is concluded that the PCB technology based 3D positive ion detector can be used a device to diagnose breast cancer.

   P-234: Assessment of Thyroid Doses from Supraclavicular Field Irradiation of Post-Op Breast Cancer Patients Using Nano Dot- OSLD Top

R. Gomathi, Mary Joan, K. Ananth1, Arun Chougule

Department of Radiological Physics, SMS Medical College and Hospital, 1SEAROC Linear Accelerator Center, SMS Medical College and Hospital, Jaipur, Rajasthan, India. E-mail: [email protected]

Objective: The assessment of surface dose to critical organs or organs at risk in the treatment or close to treatment field is essential in radiotherapy to avoid deterministic effect or to reduce the severity of side effects from radiation treatment. The objective of this study was to investigate the absorbed dose to thyroid of Post operative breast cancer patients undergoing Supra clavicular Field (SCF) irradiation by Conformal External Beam Radiation Therapy (3DCRT). Optically Stimulated Luminescence Dosimeters (OSLDs) were used for the measurements.

Materials and Methods: In this study measurement of thyroid dose received by 10 female patients undergoing conformal external beam radiotherapy for breast cancer with supraclavicular lymph node involvement were done. For each measurement the OSLD disc was placed on the surface of the thyroid gland and Surface Dose (SD) to thyroid from supraclavicular field irradiation was measured. The measurements were performed for three treatment fractions and averaged. The total dose to thyroid was estimated by multiplying it with the total number of fractions. The relationship of the OSLD measured dose and the radiotherapy treatment field was analyzed.

Results and Discussion: Thyroid is a radiosensitive organ and the most common radiation-induced thyroid dysfunction, affects 20–30% of patients undergoing curative radiotherapy to the neck region, with approximately half of the events occurring within the first 5 years after radiotherapy. Wartofsky et al. have reported that a dose about 400 mGy can increase benign and malignant thyroid tumors. Hancock et al. reported that doses to the thyroid gland that exceeded 26 Gy produce hypothyroidism. Turner et al. reported that vascular damage and follicular cell damage followed radiation doses as low as 2.25 Gy. In the present study the mean maximum thyroid dose observed was almost 300-400cGy so it is possible that some patients will develop thyroid disorders after irradiation.

Conclusion: According to Radiation Therapy Oncology Group (RTOG) protocols, the maximum thyroid absorbed dose should be less than 3% prescribed dose, but in this study, the thyroid absorbed dose was about 6%. Doses to organ at risk such as thyroid which is in the supraclavicular field should be carefully evaluated and measures should be taken to minimize the dose. Accurate surface dose estimation could also help to avoid unnecessary skin reactions such as erythema, desquamation and necrosis.

   P-235: A Simple and Economic Technique for Annealing OSLD Nano Dots Top

C. Senthamil Selvan, C. S. Sureka, U. Selvaraj1

Department of Medical Physics, Bharathiar University, 1Department of Radiation Oncology, Sri Ramakrishna Hospital, Coimbatore, Tamil Nadu, India. E-mail: [email protected]

Introduction: The Optically Stimulated Luminescence (OSL) technique has been used extensively in personnel monitoring, dosimetry of radiation accidents and dating. Optically stimulated luminescence dosimeters (OSLDs) offers many advantages include faster readout of OSLDs, re-evaluation of the detectors and better signal to noise ratio using the pulsed OSL technique, etc., over Thermo Luminescence Dosimeters (TLD) that are used widely in radiotherapy and radiology. The most commonly used material in OSL dosimetry is Al2O3:C. These nanoDots are reusable and need to be annealed effectively prior to its usage.

Objectives: To analyze the suitability of Light Emitting Diode (LED) of various color to anneal OSLD nanoDots and find the best wavelength of LED and required time for effective annealing.

Materials and Methods: A Primus linear accelerator (Siemens Medical Systems, Concord, CA, USA) was used for irradiation and InLight microStar reader (Landauer, Inc., Glenwood, USA) was used to read the OSLDs signals with the reader warm up time of 10 min. The nanoDots were irradiated at various doses include 50, 100, 150, 200, 300, 500 and 1000 cGy. For each exposure 8 nanoDots were placed at the Dmax of 100 cm SSD, field size 10 × 10 cm2 and 10 cm thickness of PMMA slab were used for backscatter in all irradiation. Then, the nanoDots were read by the OSLD reader to note the initial value. Then, these irradiated nanoDots were annealed using the LED (24 W) of Red, Green, Blue and white colors for analysis.

Results and Discussion: The PMT counts measured just before annealing the nanoDots those were irradiated to 50, 100, 150, 200, 300, 500 and 1000 cGy dose was 37287, 74590, 111684, 152637, 239007, 395893 and 847262 respectively. Then, the PMT counts after annealing those nanoDots using Red, Green, Blue and white LEDs over 45 minutes are (183, 195, 211, 227, 231, 250 and 294), (148, 159, 164, 182, 197, 225 and 243), (126, 145, 153, 172, 184, 193 and 217) and (153, 168, 181, 204, 221, 257 and 283) respectively. From this data, it is observed that the order of annealing efficiency of various LEDs is blue, green, red and white. This is due to the higher wavelength and energy of blue photons than others. Even though the trace PMT counts remained with LED based annealing are doubled than the conventional annealing setup, the LED based annealing has many advantages such as shorter time for annealing (6 hrs for commercially available annealing device), lesser heat production, lesser risk to nanoDots, more comfortable and highly economic (the total cost of LED setup is ~Rs. 500 /- and of commercially available annealing device is Rs. 0.5 Lakhs).

   P-236: Monte Carlo Simulation Of Electron Beam Using GEANT4 Top

Nitin Garg, Parsee Tomar, Arun S. Oinam, Vivek Kumar1

Department of Radiation Therapy, Regional Cancer Center, Postgraduate Institute of Medical Education and Research, 1Centre for Medical Physics, Panjab University, Chandigarh, India. E-mail: [email protected]

Introduction: Monte Carlo simulation is a technique used to model the probability of different outcomes in a process that can-not be easily predicted due to intervention of random variables. So it is assumed that Monte Carlo can provide both accurate and detailed calculations of the particle fluence from the treatment head of a radiotherapy linear accelerator. GEANT4 Software helps in simulation of treatment head with the same configuration provided by the Varian Medical Systems Inc., Palo Alto, CA, which is under confidential agreement. Monte Carlo simulation is performed to calculate the dose distribution in the water phantom of size 30 × 30 × 30 cm3 for different field sizes 10 × 10 cm2, 15 × 15 cm2, 20 × 20 cm2, 25 × 25 cm2 and for energies 6 MeV, 9 MeV, 12 MeV, 15 MeV, 18 MeV, with electron applicator. The Other parameters like the Range of the Electron beam, Mean energy, Most probable energy are also calculated and compared with the measured which is obtained from the Clinac iX, Trilogy STX installed in our facility.

Objective: The aim of the study is to verify the deviation in the percentage depth dose distribution curve, the beam profile and all the other parameter related to the range of the electron derived from the R50 as obtained by the GEANT4 simulation and the actually measured in the water phantom.

Materials and Methods: A computer with processor speed 2.2GHz, RAM 4Gb and Geant4 software version 10.02 is used for the simulation. Medical Linear accelerator Varian Medical Systems Inc., Palo Alto, CA, is simulated. For dose calculation a simulated water phantom is used which is placed at SSD = 100 cm and phantom is divided into voxel size of 0.1 x 0.1 × 0.1 cm3 which acts as the sensitive detector and record the events. For the verification of the dose distribution Blue Phantom, IBA and Trilogy STX is used. Percentage Depth dose distribution and Beam profiles are obtained using the software OmniPro I'mrt System Version 1.7b. The data recorded was analyzed using the ROOT software and analysis is done for the number of points satisfying the criterion 3% in 3 mm.

Results and Discussion: Simulation process has been started. More the number of particles run more accurate is the result. As it is time taking due to system limitation and all other parameters. The results are expected to be comparable with measured data.

   P-237: Basic Characteristics in Dosimetry of the Surface Radioactive Source Top

Hiroki Ohtani, Takao Kono1, Takahiro Hirayama1

Teikyo University, 1Japan Shield Technical Research Co. Ltd., Tokyo, Japan. E-mail: [email protected]

Introduction: Three general rules of a radiation protection are the distance, time and shelter. The attenuation of radiation is based on inverse square law of the distance in theory, but this is a thing by a point source. Since it's necessary to treat as the surface radioactive source in the medical treatment for which many radioactive sources are used, and it influences the value of the leak dose distribution in a radiation irradiation room. When using several kinds of radioisotope, radiation exposure by radiation from which the energy is different in wide range shows. The purpose of this research is to make the basic characteristics necessary to a dose assessment of the surface radioactive source clear.

Materials and Methods: Radiation dosimetry every size of the surface radioactive source and distance between the radioactive source and the detector. It was made the surface radioactive source by arranging 8 of 60-Co sealed up in a circle each 45 °. A detector was installed on the circular center where the radius was set to 20 cm from 4 cm and dosimetry was performed. Used detectors are the HDS-101G which arranged CsI scintillator and a semiconductor detector (million technology company) and a NaI scintillator (Hitachi ALOKA company). The degree of radiation incidence angle to the detector was considered and the distance between the radioactive source-detector was set to at most 46 cm. Radiation dosimetry of 60-Co-137-Cs mix area radioactive source That installs 60-Co and 137-Cs alternately, and is the surface radioactive source. A detector was installed on the circular center where the radius was set to 20 cm from 4 cm and dosimetry was performed. The detector is same as the previous method. The distance between the radioactive source-detector was set to 25 cm.

Results and Discussion: The dose decreased so that the radius of the surface radioactive source became long. The ratio which decreased most was 9.46%. This is for decrease by the radiation incident on a detector slantingly. When the distance between the radioactive source-detector became short, it was increase of the radiation dose. This reason is decrease of the radiation dose escaping to detector outside. The radiation dose by the point source isn't based on inverse square law of the distance. The tendency of the measure by the Sievert unit and the tendency by the cps unit were different in a result of measurement of 60-Co-137-Cs mix area radioactive source. The factor by the difference in the energy influences this.

Conclusion: The basic characteristics of dosimetry were made clear about inverse square law of the distance and a mix radioactive source as basic characteristics necessary to a dose assessment of the surface radioactive source in this research. The radiation dose of the surface radioactive source isn't based on inverse square law of the theoretical distance. It's also same to the size of the lateral direction of the surface radioactive source. A dose assessment by a mix radioactive source was affected by the energy of the radioactive source and arrangement.

   P-238: The Effect Of Sildenafil On Persistent Pulmonary Arterial Hypertension In Patients Post Balloon Mitral Valvuloplasty Top

Garvit Garg, Krunal, Sejal Sejwani, Jayesh Rawal1

Department of General Medicine, 1Department of Cardiology, Sumandeep Vidyapeeth University, Baroda, Gujarat, India. E-mail: [email protected]

Introduction: Pharmacological means of treating pulmonary arterial hypertension includes various drug groups like pulmonary vasodilators and diuretics, although their role is under clinical scrutiny. However, they cause potential adverse effects in the form of systemic hypotension and hypoperfusion of vital organs. Various studies are going on for the efficacy of oral sildenafil in treating secondary pulmonary hypertension. In this study we tried to evaluate the efficacy of oral sildenafil in patients who underwent balloon mitral valvuloplasty (BMV).

Aim: To see the effect of sildenafil on persistent pulmonary arterial hypertension in patients post balloon mitral valvuloplasty.

Materials and Methods: This is a prospective cohort study in which we enrolled cases that underwent Balloon mitral valvuloplasty (BMV) from June 2014 to December 2015. Total 31 patients, 11 were males and 20 were females, with mean age of 26 years. These patients were evaluated for the level of symptoms, echocardiography (ECHO), 6 mins. walk test (6MWT) and Tricuspid Annular Plane Systolic Excursion (TAPSE). These study parameters were assessed in OPD at 6, 12 and 18 months of follow-up after the procedure. The average period of starting Tab. Sidenafil was 6 months in our study group. Patients in the study group were given oral Sildenafil 25 mg once daily for 1 week followed by 50 mg once daily after the 18 months evaluation post procedure.

Results: Out of these 31 patients, 8 were in NYHA class II, 17 patients in NYHA class III and 6 patients were in NYHA class IV. All of these 31 patients who had no improvement in WHO functional class received Sildenafil. Average pulmonary artery systolic pressure (PASP) was 51 mmHg. Out of total 31 patients, 58.1% of patients in NYHA class II showed improvement, 35.5% NYHA class III patients showed improvement and in NYHA class IV show 6.4% after 18 month from the baseline. Mean value of TAPSE at baseline was 8.96 mm which increased to 14.6 mm after 18 months follow up (P=0.002), and average 6MWT was 217.7 meters at baseline which increased to 370.9 meters at the end of 18 months from the baseline.

Conclusion: In this study we conclude that there is significant role of sildenafil in improvement of PAH in patient which are gone BMV on the basic of improvement in our assessment parameters like NYHA class, TAPSE, 6MWT.

   P-239: Monte Carlo Simulation of the Photon Beam Quality Using GEANT4 and Comparison with the Actual Linear Accelerator Top

Amanjot Kaur, Gaurav Trivedi, Arun S. Oinam, Vivek Kumar1

Department of Radiotherapy, Regional Cancer Center, Postgraduate Institute of Medical Education and Research, 1Centre for Medical Physics, Panjab University, Chandigarh, India. E-mail: [email protected]

Introduction: Monte Carlo simulation is a technique used to model the probability of different outcomes in a process that can-not be easily predicted due to intervention of random variables. So it is assumed that Monte Carlo can provide both accurate and detailed calculations of the particle fluence from the treatment head of a radiotherapy linear accelerator. GEANT4 Software helps in simulation of treatment head with the same configuration provided by the Varian Medical Systems Inc., Palo Alto, CA, which is under confidential agreement. Monte Carlo simulation was performed and the dose distribution in water phantom along the central axis was calculated.

Objective: The aim of the study was to observe the deviation in the TPR20/10 simulated by GEANT4 Software to the TPR20/10 calculated from commissioned data of linear accelerator installed in the department.

Materials and Methods: A computer with processor speed 2.2GHz, RAM 4GB and Geant4 software version 10.02 was used for the simulation of the Medical Linear accelerator Varian Medical Systems Inc., Palo Alto, CA. Dose distribution (PDD) and photon beam quality (TPR20/10) will be calculated in this simulated water phantom using simulated gantry head. This calculated beam quality will be compared with the beam quality measured using the ionization chamber in the actual water phantom and commissioned data of the machine.

Results and Discussion: The results are expected to be good in accordance with allowed variation in TPR20/10 and the same will discussed later on.

   P-240: Radiation Induced Hematological Alterations in Mice and Their Prevention by Delonix Regia Extract Top

Itisha Vijayvargiya, Jaimala Sharma

Department of Zoology, Radiation and Cancer Biology Laboratory, University of Rajasthan, Jaipur, Rajasthan, India. E-mail: [email protected]

Introduction: The ionizing radiation has been exploited in various aspects of human life such as in medical and for industrial purposes. Delonix regia (plant), commonly known as Gulmohur, consists of a variety of free radical scavenging phyto-constituents like sterols, phenolic compounds, triterpenoids and flavonoids.

Aims and Objectives: The present study was focused to on investigation of the anti-oxidative and antiradiation potential of Delonix regia flower extract (DRE) giving orally on before ionizing irradiation.

Materials and Methods: Swiss albino mice were exposed to 3.0 Gy gamma radiation to serve as the irradiated control (Group I), while the other group received DRE (200 mg/kg b. wt./day) orally for 7 consecutive days half an hour before 3.0 Gy gamma irradiation (Group II). Animals were autopsied at different intervals between 24 hrs to 30 days after irradiation.

Results: Irradiated animals were found to have decreased hematological constituents like erythrocyte count, total leucocyte count, hemoglobin content and hematocrit value at various autopsy intervals. It was observed that DRE pretreatment effectively prevented radiation-induced alterations in blood.

Conclusion: Based on the results obtained in the present study it can be concluded that Delonix regia flower extract have the protective effect on hematological alterations caused by gamma radiation.

   P-241: Evaluation of Cytological Changes During Radiotherapy for Oral Cavity Cancers Top

Rajni Verma, Maryem Abid1, Mary Joan, Gurvinder Singh, Gourav Jain, Suresh Kumar Akula, Arun Chougule

Departments of Radiological Physics and 1Pathology, SMS Medical College and Hospitals, Jaipur, Rajasthan, India. E-mail: [email protected]

Aim: The study was designed to analyze various Cytological changes with radiation doses in patients treated with Radiotherapy for oral cancers. Also, the present study radio biologically verified the planned and expected treatment outcomes of Radiotherapy by cell cytology.

Materials and Methods: 70 Male cancer patients in the age group 35-50 years with oral cavity cancers are observed in the study. 10 normal samples were kept as controls. All patients were treated with conventional radiotherapy. Serial scrape smears are collected three times per patient; before treatment, middle of treatment and on completion of treatment. These smears were analyzed after Giemsa staining with the help of microscope with digital imaging facility.

Results and Conclusions: The cytological parameters such as Cytoplasmic Vacuolation, Leucocytic Infilteration, Micronuclei, Karyorrhexis, Multinucleation and Nuclear Budding were observed and evaluated with dose. It was found that all the parameters increases with dose given but increment in first half of the treatment process (pre to middle fraction of treatment) was linear with steep slope and after that it started to saturate. This nature of cell response to radiation dose indicates that accelerated radiotherapy may be a better option to treat these malignancies. 49 patients observed in this study were histo pathologically proven squamous cell carcinoma and shown considerable increase in various cytological parameters with radiation. This demonstrated that radiation treatment response is better in well differentiated cancers in comparison to poorly differentiated cancers. Increased chance of recurrence is indicated by presence of dysplastic cells, hyper-chromatic nuclei, irregular nuclear outline, small dark tumor cells or large naked ovoid nuclei. All the patients observed in this study are having an addiction to either tobacco chewing or smoking or both which shows a strong correlation between tobacco use and these malignancies. In this study the selected patients were treated with chemotherapy simultaneously. Out of the 70 patients, 47 patients were treated with 3 cycles of chemotherapy, 13 patients with 4 cycle of chemotherapy and 10 patients with 5 cycle of chemotherapy. This was a limitation of this study. The study needs to be continued to eliminate this limitation.

   P-242: The Effect of Electromagnetic Radiation Frequencies of 900 MHz from Mobile Phone on the Blood of Swiss Albino Mice Top

Niharika Sharma, Jaimala Sharma

Department of Zoology, Radiation and Cancer Biology Laboratory, University of Rajasthan, Jaipur, Rajasthan, India. E-mail: [email protected]

Aim: To evaluate effect of electromagnetic radiation from mobile phones on Swiss albino mice.

Introduction: Cellular wireless telephones are based on widespread networks of base stations that connect the users through Radio Frequency (RF) signals, which expose to RF in general and radiations from base stations become great deal of concern about possible consequent health effects in human beings.

Materials and Methods: Animals (Swiss albino mice) of 6-8 weeks of age from an inbred colony were selected and were divided into two groups- (i) Sham irradiated (without mobile phone radiation) (ii) Mobile phone irradiated (for 60 days - 2hours/day). The mice were exposed to mobile phone radiation daily for 2 hours per day for 60 days with CDMA Mobile phone (Group II). After the exposure period the animals were sacrificed at different intervals between, 1-60days and blood was collected to estimate various hematological parameters.

Results: in Group II (Radiation exposed), total leucocytes counts (TLC), differential leucocytes counts (DLC), erythrocyte (RBC) counts and hemoglobin percentage, were significantly declined as compared to Group I (Shame exposed). In Group I no remarkable change was observed.

Conclusions: On the basis of the results obtain in this study it can be concluded that EMR frequency of 900 MHz emitted from CDMA mobile phone decreased TLC, DLC, RBC and hemoglobin percentage in the exposed mice.

   P-243: Protective Effect of Carissa Carandas Extract Against DMBA/TPA Induced Skin Carcinoma in Swiss Albino Mice Top

Tanuja Jain, Jaimala Sharma

Department of Zoology, Radiation and Cancer Biology Laboratory, University of Rajasthan, Jaipur, Rajasthan, India. E-mail: [email protected]

Aim: The current study was designed to elucidate preventive effect of orally administered Carissa carandas extract (CCE) at a dose rate of 50 mg/kg b.wt./day on a two-stage skin carcinogenesis model in Swiss Albino mice against 7,12 dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) induced squamous cell carcinoma.

Introduction: Carissa carandas , belongs to Apocynaceae family and popularly known as Karaunda, possess various pharmacological properties.

Materials and Methods: The mice were divided in two groups. Topical application of DMBA (100nmol/100μl of acetone) for two weeks, followed by TPA application (1% in acetone/ thrice in a week) throughout the experiment i.e. 16 weeks, induced skin lesions, on the depilated back of mice (Group I). Oral administration of CCE (Group II) at the dose rate of 50mg/kg body weight at the peri-initiational stage (i.e., 7 days before & 7 days after DMBA application). Histopathology of tumors was evaluated in the treatment groups.

Results: Treatment of animals in Group II (oral administration of CCE of 50 mg/kg b.wt./day) reduced the skin papillomas, also delayed tumor formation and tumor growth in CCE treated experimental group (Group II). Histopathological study revealed that epidermal hyperplasia, keratinized pearl formation, and acanthosis in skin and tumors were observed in carcinogen treated animals whereas these were found to be reduced after CCE administration.

Conclusions: These results proved that CCE protected against DMBA/TPA induced skin carcinogenesis by reducing adverse histopathological alterations during skin carcinogenesis process in Swiss albino mice of Group II as compared to carcinogen treated animals (Group I).

   P-244: Dosimetric analysis of unflattened (FFFB) and flattened (FB) photon beam energy for Gastric cancers using IMRT and VMAT – A comparative study Top

Manindra Bhushan1,2, Girigesh Yadav1, Deepak Tripathi2, Kothanda Raman1, Lalit Kumar1, Munish Gairola1

1Medical Physics Division & Department of Radiation Oncology, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, 2Amity Institute of Applied Sciences, Amity University, Uttar Pradesh, India. E-mail: [email protected]

Introduction: Gastric carcinomas contribute a large patient population worldwide. Evolution of megavoltage accelerators has provision of photons of desired energy. IMRT has ability to cover the target and spare the nearby critical organs. Advancement in technology has introduced VMAT which allows continuous treatment delivery with modulated intensity map. Usually 6MV_FFB energy is used for the treatment planning in abdominal malignancies; however flattening filter free (FFF) 6MV beam is gaining momentum for the treatment of such cases, due to their advantage of higher dose rate than 6MV beam.

Objectives: The aim of present study is to evaluate the feasibility of flattening filter free beam (FFFB) for the treatment of gastric tumors and to review their benefits over 6MV flatten beam (6MV_FFB).

Material and Methods: 15 patients with Gastric carcinoma were selected for the study. CT scans of thickness of 0.3 cm. were acquired in supine position. PTV and OAR's were delineated. All the plans were made retrospectively for each patient for the prescription dose of 45 Gy/25 fractions to the PTV. Four isocentric plans were compared in the present study on Varian TrueBeam Linear accelerator (Varian Medical Systems, Palo Alto, California, USA).

Results: PTV D98% was 44.41 ± 0.12 Gy, 44.38 ± 0.13 Gy, 44.59 ± 0.14 Gy and 44.49 ± 0.19 Gy for IMRT 6MV_FFB, IMRT 6MV_FFFB, VMAT 6MV_FFB and VMAT 6MV_FFFB respectively. 6MV_FFFB beam minimizes the mean Heart dose Dmean (P=0.001). It was observed for Spinal cord that VMAT reduces Dmax (P=0.002) and D<2cc (P=0.001) significantly as well as for Liver, VMAT plans have reduced the mean dose Dmean (P=0.022) and D>700cc (P=0.001). VMAT dominates over IMRT when it came to kidney doses V12Gy (P=0.02), V23Gy (P=0.015), V28Gy (P=0.011) and Dmax (P<0.01). VMAT has significantly reduced the doses to kidneys. It was analyzed that 6MV_FFFB significantly reduces the dose to normal tissues (P=0.006 & P=0.018). VMAT significantly reduces the TMU, required to deliver the similar dose by IMRT (P<0.01).

Discussion: Simultaneously changing multi-leaf position and dose-rate helps to achieve the optimum solution in VMAT. This study demonstrated that 6MV_FFB and 6MV_FFFB provided similar dose coverage, homogeneity and conformity whether they are used with IMRT or VMAT. Daniel et al found similar results while using hypo-fractionated VMAT using flattening filter free beam in prostate cancers. Cold-spots were reduced with VMAT due to rotational nature of the treatment. For the critical structures like common lung, heart, liver and kidneys; mean dose reduced significantly with VMAT unflattened beam. This may be possible due to non-deposition of un-necessary dose to the area outside the PTV. Reduced low-dose region of kidney and bowel with 6MV FFF lowers the risk of secondary cancers. Although TMU increased slightly in FFF, yet unfiltered beam made it possible with availability of higher dose rate. Our data demonstrated that the time required to deliver the same dose is 5.62 times higher in IMRT 6MV, 2.93 times higher in IMRT 6MV FFF and 1.95 times higher in VMAT 6MV when compared with VMAT 6MV FFF.

Conclusion: Unflattened beam spares the organs at risk significantly to avoid the chances of secondary malignancies and reduces the intra-fraction motion during treatment due to provision of higher dose rate. Hence, we conclude that 6MV unflattened beam can be used to treat gastric carcinoma.

Daniel RZ, Stephanie L, Jan H et al . Use of photon beam of a flattening filter-free linear accelerator for hypofractionated volumetric modulated arc therapy in localized prostate cancer. Int J Radiat Oncol Biol Phys 2012; Vol.83,No.5, pp.1655-1660.

   P-245: Synthesis And Thermoluminescence Properties of Rare Earth Doped (Tb, Dy) Doped Fluoroperovskite NaMgF3 Top

Aayushi Jain, Pooja Seth, Shruti Aggarwal

University School of Basic and Applied Sciences, GGSIPU, New Delhi-110078, India. E-mail: [email protected]

Introduction: Thermoluminescence dosimetry (TLD) is a potential method for the measurement of absorbed dose in the field of medical physics, personal dosimetry and environmental monitoring. This has encouraged the search for new sensitive thermoluminescent (TL) material with good dosimetric properties. A worldwide progress has been made in this direction for the development of TL dosimeter by applying different preparation route and dopant ions. Fluoroperovskite, NaMgF3 is one of the important material due to its interesting properties such as non toxicity, less hygroscopicity, high thermal durability and wide band gap. NaMgF3 is a tissue equivalent (tissue equivalent Zeff ~ 10.32) material and its mass attenuation coefficient is similar to that of water for photon energies above 0.1 MeV. These useful properties allow its potential application in the field of radiation therapy and radiodiagnostics for the dose monitoring and measurement.

Objectives: To synthesize fluoroperovskite, NaMgF3 doped with rare earth ions Tb and Dy using solid state diffusion method. To investigate the effect of dopant ion (Tb and Dy) on thermoluminescence (TL) properties of NaMgF3.

Materials and Methods: Powder samples of NaMgF3, NaMgF3:Tb (0.5 mol%) and NaMgF3:Dy (0.5 mol%) were prepared by solid state diffusion method. Starting materials NaF and MgF2 were taken in equimolar stoichiometric ratio. Dopants Tb in the form of TbCl3.6H2O & Dy in the form of DyCl3.xH2O were used. The mixture was heated in an alumina crucible at 1043 K for 12h. The solid formed was then crushed to obtain powder of NaMgF3, NaMgF3:Tb (0.5 mol%) and NaMgF3:Dy (0.5 mol%). XRD pattern were taken from model Rigaku Ultima IV. The assynthesized samples were annealed at 400°C for 15 min and irradiated with a gamma dose of 15 Gy from 60Co source. A Harshaw Q TLD reader model 3500 was used for recording of TL glow curves.

Results and Discussion: X-Ray Diffraction: Powder XRD pattern of assynthesized NaMgF3, NaMgF3:Tb3+ and NaMgF3:Dy3+ matches well with standard JCPDS data (No. 82-1224 ) as shown in [Figure 1]. XRD pattern confirms the formation of NaMgF3. Addition of dopant Tb and Dy does not change the host lattice. Themoluminescence (TL): NaMgF3 showed a simple glow curve structure with a single peak at 127°C. The glow curve structure changes after doping with Tb and Dy, a new high temperature peak appears at 292°C and 279°C with Tb and Dy, respectively as shown in [Figure 2]. However, main TL peak position was approximately same in all the samples. From the glow curve structure, it is observed that with Tb dopant, TL intensity is increased by a factor of 2.2 and with Dy dopant, TL intensity is increased by a factor of 1.6 in comparison to undoped NaMgF3.
Figure 1: XRD pattern of NaMgF3, NaMgF3:Tb (0.5 mol%) and NaMgF3:Dy (0.5 mol%)

Click here to view
Figure 2: TL glow curve of NaMgF3, NaMgF3:Tb (0.5 mol%) and NaMgF3:Dy (0.5 mol%)

Click here to view

Conclusion: In this paper, NaMgF3, NaMgF3:Tb and NaMgF3:Dy were successfully synthesized by solid state diffusion method. A preliminary investigation of thermoluminescence properties such as glow curve structure, peak intensity and peak position were done. From the glow curve structure, it is found that doping of Tb showed better results in comparison to Dy as it increases the TL sensitivity of NaMgF3 by a factor of 2.2. Encouraged by these results, further investigations on dosimetric properties of NaMgF3 and related kinetic parameters will be made.

   P-246: Biochemical Changes in Brain of Swiss Albina Mice Exposed to 2.45 GHz Microwaves Radiation Top

Rajendra Jat, Najendra Singh, Rashmi Sisodia, Deepak Bhatnagar1

Department of Zoology, University of Rajasthan, Jaipur, 1Department of Physics, University of Rajasthan, Jaipur, India. E-mail: [email protected]

Objectives: Exploration of the changes in biochemical parameters of brain exposed to 2.45 GHz microwave radiations.

Material and Methods: 6-8 weeks old male Swiss albino mice, weighing 25.0 ±2.0 grams were procured from inbred colony. Mice were divided into two groups (6 mice in each group). Group 1) Sham exposed, and group 2) microwave exposed group. Microwave radiation experimental bench was used for the exposure to mice. Exposure was given in plexiglas cages. Mice were exposed to 2.45 GHz microwaves radiations for 2 hrs/day for 15 days with power density as 0.25 mW/cm2 and specific absorption rate (SAR) to be 0.072 W/kg. Catalase (CAT), Lipid per oxidation (LPO), Glutathione (GSH) and superoxide dismutase (SOD), assays were performed to observe biochemical changes.

Results: A significant increase (P < 0.001) in Catalase (CAT) and in Lipid per oxidation (LPO) and a significant decrease (P < 0.001) in Superoxide dismutase (SOD), Glutathione (GSH) were observed in exposed group in comparison to control group

Conclusion: It may be concluded that microwaves at 2.45 GHz frequency cause oxidative stress mediated cellular toxicity which leads to adverse and detrimental biochemical changes in brain.

Keywords: Microwave radiations, CAT, SOD, LPO, GSH

   P-247: Biochemical Changes in Blood of Swiss Albina Mice Exposed to 2.45 GHz Microwaves Radiation Top

Najendra singh, Rajendra Jat, Rashmi Sisodia, V. K. Saxena1

Department of Zoology, University of Rajasthan, Jaipur, 1Department of Physics, University of Rajasthan, Jaipur. E-mail: [email protected]

Objectives: The objectives of this study were to explore the changes in biochemical parameters of Blood exposed to 2.45 GHz microwave radiations.

Material and Methods: 6-8 weeks old male Swiss albino mice, weighing 25.0 ±2.0 grams were procured from inbred colony. Mice were divided into two groups; (6 mice in each group) 1) Sham exposed, and 2) microwave exposed group. Microwave radiation experimental bench was used for the exposure to mice. Exposure was given in Plexiglas cages. Mice were exposed to 2.45 GHz for 2 hrs/day for 15 days with power density as 0.25 mW/cm2 and SAR to be 0.072 W/kg. Blood sugar, Total protein, Acid phosphatase, and alkaline phosphatase (ALP) assays were performed to observe biochemical changes.

Results: A significant decrease (P < 0.001) in Blood sugar, Total protein, and Acid phosphatase (ALP) and increase (P < 0.001) levels of Alkaline phosphatase (ALP) were observed in exposed group in comparison to control group.

Conclusion: It may be concluded that microwaves at 2.45 GHz frequency causes oxidative stress mediated cellular toxicity which leads to adverse and detrimental biochemical changes in Blood.

Keywords: Microwave radiations, Blood sugar, Total protein, Acid phosphatase, ALP.

   P-248: Lung SBRT – Dosimetry and Delivery comparison of Rotational IMRT technique from Linear Accelerator and Tomotherapy. Top

Rajesh Kinhikar1, Priyadarshini Sahoo1, Naveen Mummudi, Deepak Deshpande1, Jai Prakash Agarwal

Departments of Radiation Oncology and 1Medical Physics, Tata Memorial Hospital, Parel, Mumbai, India. E-mail: [email protected]

Introduction: Stereotactic body radiation therapy (SBRT) for lung demands high precision dose delivery technique to minimize the doses to organs at risk (OARs), while simultaneously enabling dose escalation to target. These techniques employ either intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT). Aim of this study was to evaluate the plans based on dosimetric indices for rotational IMRT delivered with tomotherapy and VMAT (RapidArc) with Linac for SBRT in early stage non-small cell lung cancer (NSCLC).

Materials and Methods: Fifteen Patients (stage I NSCLC with peripherally located lesion) treated with Rapid Arc SBRT using 6 MV X-rays with one/two partial-arc plan (180°) in Linac (with maximum dose rate of 600 MU/Min) were included. To determine the optimal treatment modality, a new treatment plan was generated using IMRT with HT for each patient for comparative purpose. For HT plans, the field width of 2.5 cm, pitch as 0.1 and modulation factor as 2.5 was used. Dosimetric indices compared were conformity index, homogeneity index, D2cm and R50% for PTV. For Lung-PTV and Heart- V20, V5, mean dose were evaluated and for other OARs (Esophagus, trachea and spinal cord), Dmax was compared. Dosimetric accuracy was assessed using gamma index (3% dose difference, 3 mm DTA, 10% threshold) and point dose measurement for HT plans (3% tolerance).

Results and Discussion: Mean volume of PTV was 84 cc (range 24cc-158cc). Mean CI, HI, R50% for PTV with HT plan were1.16 (SD 0.18), 1.02 (SD 0.01) and 5.65 (SD 0.98) respectively. With Rapid Arc, mean CI, HI and R50% were found to be 0.83 (SD 0.35), 1.14 (SD 0.08) and 4.6 (SD 1.1) respectively. D2cm was comparable with both the technologies. R50 was slightly on higher side in HT plan. MU for HT is around 8-9 times more than RA. Delivery of a 7.5 Gy fraction required an average of 19.97 min (HT) and 3.2 min (Rapid Arc). All verification plans were well within tolerance dosimetrically. Isodose distribution (90%) for RapidArc (RA) Isodose distribution(90%) for TOMO are shown in [Figure 1].
Figure 1: Isodose distribution(90%) for RA, Isodose distribution(90%) for TOMO

Click here to view

Conclusions: Both high precision radiotherapy techniques with Helical Tomotherapy and Linac were capable of achieving the desired goals. However, HT plans showed relatively better conformity compared to Rapid Arc. Doses to OARs were minimal with Rapid Arc. Shorter treatment time with Rapid Arc may have the patient comfort.

   P-249: Dosimetric dependence on collimator angle in volumetric modulated arc therapy of head and neck cancers Top

Resmi K. Bharathan, Arya Devi, Silpa Ajaykumar, Suja C. A, Soumya N. M, Geetha M

Department of Radiation Oncology, Malabar Cancer Centre, Thalassery, Kerala, India. E-mail: [email protected]

Introduction: Multileaf collimators (MLC) are the best tool for beam shaping, and an important way to minimize the absorbed dose to healthy tissue and critical organs. They have moveable leaves arranged in pairs that can block a certain part of beam. Owing to its ability to control leaf position and with a large number of controlled leaves, it can be used to shape any desired field. During VMAT the linear accelerator (LINAC) control system changes the dose rate and the multi leaf collimator (MLC) positions while gantry is rotating around the patient. Collimator angle is usually rotated in the plans of VMAT to reduce radiation leakage between MLC leaves. At a zero angle, the leakage between MLC leaves accumulates during the gantry rotation and the summed leakage results in unwanted dose distributions, which cannot be controlled by optimization. At different collimator angles, the unwanted doses can be controlled by dose constraints in the optimization procedure so that we can reduce the unwanted doses. The optimal collimator angle for VMAT plan is thus required to be determined.

Objective: The purpose of this study is to investigate the dose-volume variations of planning target volume (PTV) and organs-at-risk (OARs) in prostate volumetric modulated arc therapy (VMAT) while varying the collimator angle.

Methods and Materials: The key study variables include the coverage of the PTV and doses to the OARs in the plans with different collimator angles (10, 20 and 45 degree) of 30 patients. The dosimetric comparison was carried out using the following parameters such as dose to 98% of the PTV (D98%), dose to 50% of the PTV (D50%), dose to 2% of the PTV (D2%), maximum dose (Dmax), mean dose (Dmean), Conformity Index (CI), Homogeneity Index (HI), Gradient index (GI) and Monitor Units (MU) for the PTV for each of the collimator angle.30 patients who were already treated for head and neck cancers were selected for this study. Plans were created by changing the collimator angle. Eclipse planning system was used for creating the plans. For each change of collimator angle, a new plan was re-optimized for that angle. The treatment plan not changed for each angle, only repeated by changing the collimator angles. A 30-degree collimator angle is used in the already approved plans. The dosimetric parameters was compared across each plans using t-test and annova.

Results and Disussion: This work explores the impact of different collimator angles on VMAT plans. Collimator angle selection could play vital role in improving the quality of treatment plans. It is concluded from the results that the dose variations with the change of collimator angle are significant. VMAT plans with said collimator angles do not play a substantial role in PTV coverage but for more accuracy, a 30° collimator angle provides superior PTV dose distribution than all other studied collimator angles as shown by a better value of CI and HI. It was observed that a 45° collimator angle is appropriate for sparing of OARs. The results of our study set the groundwork for guiding the collimator angle selection with regards to PTV dose distribution and sparing of OARs in VMAT planning of Ca larynx and Ca hypopharynx cases. This work can be extended with more number of patients. This work also can be extended to other treatment sites using VMAT.

   P-250: Evaluation of Intrafractional Setup Errors in Frameless SRS Computed Using Optical Surface Monitoring System & CBCT Top

P. T. Patwe, V. Mhatre1, A. Nachankar, P. Dandekar

Sir HN Reliance Foundation Hospital & RC, Girgaum, 1Kokilaben Dhirubhai Ambani Hospital & RC, Andheri, Mumbai, India. E-mail: [email protected]

Purpose or Objective: The aim of study was to evaluate setup accuracy and intrafraction errors of patients treated with single fraction intracranial stereotactic radio surgery using the Optical Surface Monitoring System and Perfect pitch Six Degree of Freedom (DoF) couch. We compared the patient positioning shifts (translational and rotational set up error) computed by OSMS against the shifts given Cone Beam CT (CBCT).

Material and Methods: During August 2016 and May 2017, 3 patients were treated with single fraction frameless stereotactic radio surgery (SRS) at our institution. Patients were immobilized using Q fix immobilization system and Perfect Pitch 6 DoF couch platform. Q-fix immobilization system consists of Q-fix Aquaplast mask, Portrait Head & Neck base plate, MOLDCARE® Cushion & Silverman head support. MOLDCARE® Cushion used on Silverman head support provides customized head support. The cushion is composed of a soft fabric bag containing polystyrene beads. When water is sprayed over pillow, it becomes rigid conforming to the contours of patients head & neck. The OSMS is a video-based 3D surface imaging system used to detect and reconstruct the skin surface of a patient in 3D before and during the radiotherapy treatment. As shown in [Figure 1], it consists of 3 ceiling camera units positioned, two laterally to the treatment couch, and the third centrally located at the foot of the couch. A projector unit projects a red light speckle pattern onto the patient. Overall, 2 image sensors located on either side of the projector acquire the image of the patient and the speckle pattern. With the images from the 3cameras,the system reconstructs the 3D surface for all the gantry positions, even in the cases where the linac head interposes between one of the cameras and the isocenter, obscuring the image projection for that camera. The OSMS system was used to position the patient immediately prior to treatment & to 6 dimensionally track the patient during treatment. The Cone-Beam computed tomography (CBCT) were acquired before and after treatment to asses for set up errors. Translational and rotational set up errors were obtained in Right-Left (RL), Antero -Posterior (AP),Cranio-Caudal (CC) directions. The shifts were applied in accordance with the CBCT match results. The shifts given by CBCT match were compared with the shifts given by OSMS. Means and one standard deviation of the Intrafractional errors in all six directions were analyzed. The rotational & translational shifts given by OSMS were compared with shifts given by CBCT.
Figure 1: True Beam STx with 6DoF Perfect Pitch Couch & OSMS System

Click here to view

Results: A total of 06 CBCT scans were analyzed & compared with the shifts computed by OSMS. The couch was shifted as per the shifts given by CBCT. The OSMS computed shifts were compared with CBCT shifts. The mean & standard deviation in the shifts computed by OSMS as compared to CBCT (in mm for translation and degrees for rotation) were 0.2 ± 0.10 (RL), 0.10 ± 0.20 (PA), 0.2 ± 0.10 (CC), 0.15 ± 0.30 (Roll), 0.08 ± 0.2 (Pitch), 0.2 ± 0.3 (Rotation).

Conclusion: OSMS guided frameless SRS utilizing immobilization system like Q Fix open mask , Perfect Pitch 6DoF couch platform is precise and reproducible technique. The accuracy of shifts computed by OSMS is comparable to CBCT data.

   P-251: Measurement of Entrance Skin Doses in Common Digital Radiography Examinations & Proposed Local Diagnostic Reference Levels Top

Bhupendra Singh Rana, Sanjeev Kumar1, I. S. Sandhu2, (CC) P. Singh3, N. Khandelwal

Department of Radiodiagnosis, PGIMER, Chandigarh, 1Department of Physics, G. G. D. S. D. College, Chandigarh, India, 2Chitkara University, Punjab, 3I. K. Gjural P. T. U., Jalandhar, India. E-mail: [email protected]

Introduction: In radiology, collective radiation doses resulting from the use of X- rays in radiography, computed tomography (CT) scans and interventional procedures has maximum contribution to the medical exposures.[1] In diagnostic x ray procedures radiation doses to the patients are usually low and of the order of few μGy to tens of mGy. The low dose exposures in the radiological examinations increase the risk of stochastic effects, mostly cancer induction in exposed patients. The risk of stochastic effects primarily depends on the magnitude of radiation dose as well as on the anatomical structure irradiated.[2-4] Therefore, all the radiation exposures need to be monitored and optimized to limit the associated radiation risk to the patient without limiting the clinical utility of the diagnostic examinations.

Objective: The aim of the present work is to measure the ESDs for common radiographic examinations of adult and pediatric patients for 12 diagnostic examinations viz . chest (AP and PA), lumbo sacral spine (AP and LAT), thoracic spine (AP and LAT), cervical spine (AP and LAT), abdomen (AP), pelvis (AP), hip joints (AP), skull (AP and LAT)), knee joint (AP and Lat), wrist (AP), upper extremity (AP) and lower extremity (AP) in digital radiography (DR) setup and propose LDRL for DR.

Materials and methods: The assessment of the patient doses in present work was done in accordance with International Atomic Energy Agency (IAEA) recommended protocol[5] for radiographic exposures. We have utilized thermoluminescent dosemeters TLDs (LiF: Mg, Ti) for dose measurement to evaluate the ESDs in adult patients. For pediatric patients, ESDs were estimated from exposure parameters and tube output measurement with appropriate back scatter factor (BSF). The examinations were performed in X-ray machines installed in Department of Radiodiagnosis, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India. Information on type of examination, sex, age, height, weight of the patient, focus to table top distance (FTD), field size along with set KVp and mAs were recorded during data collection.

Results and Discussions: The measured minimum, maximum and average values of the ESD along with their third quartile values proposed as LDRLs for adult and pediatric patients. LDRL values obtained in this study were compared with published values of Health Protection Agency, UK in its report HPA-CRCE-034 (2012)[6], Italian DRL values[7] and values reported by Sonawane et al.[8]. In this study, pediatric patients are arranged into five age groups of <1months, 1-12 months, 13-60 months, 61-120 months and 121 months and above. LDRLs of this study were also compared with DRLs published by NRPB-R318 (2000)[9], Billinger et al. (2010)[10] and Wambani et al. (2013)[11]. In addition, LDRL values of this study were also compared with earlier reported DRLs for chest, abdomen (AP), skull (AP) and skull (Lat) of pediatric patients. The present study has demonstrated that use of DR technology reduces the patient's radiation exposure and helps in maintaining the ALARA principle.


National Council on Radiation Protection and Measurements. Ionizing radiation exposure of thepopulation of the United States. NCRP Report No. 160 (2009).

United Nations. Sources and Effects of Ionizing Radiation. Report to the General Assembly, with Scientific Annexes Volume II Effects: United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 2000 Report. United Nations publications Sales No. E.00.IX.3, New York (2000).

Hall, E. J. and Brenner, D. J. Cancer risks from diagnostic radiology. Br. J. Radiol. 81, 362–78 (2008).

Pearce, M. S., Salotti, J. A., Little, M. P., McHugh, K., Lee, C., Kim, K. P., Howe, N. L., Ronckers, C. M., Rajaraman, P., Craft, S. A. W., Parker, L. and De González, A. B.Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours:a retrospective cohort study. The Lancet 380, 499-505 (2012).

International Atomic Energy Agency. Dosimetry in diagnostic radiology: an international code of practice. Technical reports series No 457 (2007a).

Hart, D., Hillier, M. C. and Shrimpton, P. C. Doses to patients from medical x-ray examinations in the UK–2010 review. Health Protection Agency, HPA–CRCE-034, London. (2012).

Compagnone, G., Pagan, L. and Bergamini, C. Local diagnostic reference levels in standard X-ray examinations. Radiat. Prot. Dosim. 113(1), 54-63-94 (2005).

Sonawane A U, Shirva V K, Pradhan A S. Estimation of skin entrance doses (SEDs) for common medical X ray diagnostic examinations in india and proposed diagnostic reference lenels (DRLs). Radiat. Prot. Dosimetry 138(2), 129-136 (2010).

Hart, D., Wall, B. F., Shrimton, P. C., Bungay, D. R. and Dance, D. R. Reference doses and patient sizes in pediatric radiology. National Radiological Protection Board, NRPB-R318, London. (2000).

Billinger, J., Nowotny, R. and Homolka, P. Diagnostic reference levels in pediatric radiology in Austria. Eur. Radiol. 20, 1572-79 (2010).

Wambani, J. S., Korir, G. K., Korir, I. K. and Kilaha, S. Establishment of local diagnostic reference levels in pediatric screen film radiography at a children's hospital. Radiat. Prot. Dosim. 154(4), 465-76 (2013).

   P-252: The Proton Computed Tomography With Vipman Phantom: A Simulation Study Top

D.Q.Huy1,2, D.T.Manh1, T.C.Chao2, C.C.Lee2

1Oncology Center, 175 Military Hospital, Ho Chi Minh City, Viet Nam, 2Department of Medical Imaging and Radiological Sciences, College of Medicine, Chang Gung University, Taiwan. E-mail: [email protected]

Introduction: The proton therapy dramatically is increasing in the world. Because the range proton is a finite in matter, this treatment modality permits a comparable superiority with conventional external beam X-ray therapy. In current clinical particle, proton therapy treatment are made with pre-treatment X-ray the patient's CT scans. To convert the X-ray CT Hounsfield to proton relative stopping powers used a derived calibration function. However, the relationship between Hounsfield units and relative stopping power is not bilinear which be able to lead range uncertainties at planning timely treatment. The Proton Computed Tomography can be directly applied to treatment planning system in order to mitigate a range uncertainty. Objectives: The first, to apply the Discrete Range Modulate (DRM) method that could convert E80(energy 80%) to Water Equivalent Thickness (WET) of various simulated Proton Radiography projections. The second, developing feasibility of both Ray Tracing and Monte Carlo simulation code MCNPX/DRM method, being a simultaneous reconstruction of VIP-Man model. Material and method: Both Ray Tracing which was used to Water Equivalent Ratio (WER) as characteristic material organ in order to replace voxel by voxel of VIP-Man model and MCNPX/DRM method will be approaching similarly to set up experiment geometries. After that collecting Proton Radiography by cone-beam source that rotated VIP-Man phantom from 0 to 180 degree with step angle 4 degree. It means, 45 image projections will be carried out both methods. Finally, (Feldkamp–Davis-Kress) FDK algorithm approaches reconstructed slices of VIP-Man model. Result: Gamma index (GI) was evaluated through the Proton Radiography of Ray Tracing (WER) and MCNPX/DRM method. The pass-rate (GI) = 0.9846 with image projections at 0 degree. X-profile and Y-profile Proton Radiography also were estimated. The reconstructed slices of 45, 90, 180 projections that reconstructed by Ray Tracing method were comparable each other and the cavity hole and bone-jaw also observe clearly in the reconstructed slices, respectively. Finally, the reconstructed slice of Ray Tracing and MCNPX/DRM method with 45 projections which will be comparable with original slice VIP-Man (WER). Conclusion: No difference significant of reconstructed slice between two methods. Developed successfully Ray Tracing (WER) and MCNPX/DRM method to create the reconstructed image of Proton Computed Tomography.

Keywords: The Proton Computed Tomography, VIP-Man Phantom, Ray Tracing, MCNPX

   P-253: Small field and SABR audits by the Australian Clinical Dosimetry Service (ACDS) Top

S Manktelow, M Shaw1, S Keehan2, A Alves3, J Lehmann4, J Lye5

Australian Clinical Dosimetry Service, ARPANSA, Yallambie VIC Australia [email protected], 1Australian Clinical Dosimetry Service, ARPANSA, Yallambie VIC Australia RMIT University, Melbourne VIC Australia, [email protected], 2Australian Clinical Dosimetry Service, ARPANSA, Yallambie VIC Australia, [email protected], 3Australian Clinical Dosimetry Service, ARPANSA, Yallambie VIC Australia, [email protected], 4Calvary Mater Hospital, Newcastle NSW Australia RMIT University, Melbourne VIC Australia, [email protected], 5Australian Clinical Dosimetry Service, ARPANSA, Yallambie VIC Australia, [email protected]

Introduction: Stereotactic radiosurgery (SRS) and stereotactic ablative/body radiotherapy (SABR) are complex techniques in modern radiotherapy, with inherently higher risk to patients than conventional radiotherapy. Integrated within these techniques are the challenges involved with accurate small field dosimetry. A research project to develop small field and SABR dosimetry audits was undertaken by the Australian Clinical Dosimetry Service in order to meet this challenging area of clinical work.

Objectives: To provide information regarding the development of the ACDS small field and SABR field trials. Initial results will be discussed, including a small field chamber intercomparison undertaken at the ACDS.

Materials & Methods: The ACDS included field trials of small fields in the Level Ib audits as of September 2016. Output factors were measured with the PTW 60019 microDiamond and compared to the facility stated output factors. Profile scans and output measurements were taken for the facility defined field sizes in categories Medium (2.0-2.9 cm), Small (1.0-1.9 cm) and Very small (0.4-0.9 cm). The ACDS used SABR principles from existing literature, together with common practice observed in the Australian context, to design a SABR dosimetry audit that would meet the needs of Australian Radiotherapy facilities. An end-to-end dosimetry audit was developed using a customised CIRS® humanoid thorax phantom as shown in [Figure 1]. The audit planning cases replicate the most common tumour sites treated with SABR: lung, spine and soft tissue. Tumour shaped volumes located inside the phantom were planned by the facility for delivery with modality of choice: 3DCRT, IMRT, VMAT, DCAT, FFF. The audit planning guidelines follow current SABR clinical trials: SAFRON II [1], NIVORAD [2] and RTOG 1112 [3]. The planning cases were designed to ensure compatibility with all TPS/Linac equipment combinations currently used for SABR across Australia. Gafchromic EBT3 film, PTW 60019 microDiamond and various other small field detectors were investigated for use in the Level III audit.
Figure 1: ACDS custom CIRS thorax phantom for SBRT

Click here to view

Results: Initial results for the ACDS Level Ib small field and Level III SABR field trials will be discussed.

Discussion: Small field dosimetry will be incorporated into the existing Level Ib and Level III audits offered by the ACDS. The ACDS is a nation-wide dosimetry auditing service, supporting standardisation of SABR practice across Australia.

References/ Acknowledgements:

Trans-Tasman Radiation Oncology Group, Australasian Lung Cancer Trials Group. Amendment 4 (2016). SAFRON II – Stereotactic Ablative Fractionated Radiotherapy versus Radiosurgery for Oligometastatic Neoplasia to the Lung: A Randomised Phase II Trial (TROG 13.01/ALTG 13.001).

NHMRC Clinical Trials Centre, Australasian Lung Cancer Trials Group, Trans-Tasman Radiation Oncology Group. Version 1.1 (2015). NIVORAD – A randomised phase 2 trial of nivolumab and stereotactic ablative body radiotherapy in advanced non-small cell lung cancer, progressing after first or second line chemotherapy (ALTG 14/002/CTC 0135).

NRG Oncology, National Clinical Trials Network, National Cancer Institute. RTOG 1112 – Randomized phase III study of sorafenib versus stereotactic body radiation therapy followed by sorafenib in hepatocellular carcinoma.

   P-254: Improvement of Measurement Accuracy of Lateral Dose Profiles Using Scintillator for Carbon Pencil Beam Top

Takumi Narusawa1, Katsunori Yogo2, Tatsuaki Kanai3, Akihiko Matsumura3, Hikaru Souda3, Yosuke Kano4, Kohei Kamada1, Yuya Tatsuno1, Masami Torikoshi3, Kazushige Hayakawa1,5

1Graduate School of Medical Sciences, Kitasato University, 2Hiroshima High-Precision Radiotherapy Cancer Center, 3Gunma University Heavy Ion Medical Center, 4Accelerator Engineering Corporation, 5School of Medicine, Kitasato University. Email: [email protected]

Introduction: Scanned car