|Year : 2017 | Volume
| Issue : 5 | Page : 66-109
|Date of Web Publication||24-Oct-2017|
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
. Oral. J Med Phys 2017;42, Suppl S1:66-109
| O-1: Radiation Safety Assessment of Proton Therapy Facility in India|| |
G. Sahani, Pankaj Tandon, A. U. Sonawane
Radiological Safety Division, Atomic Energy Regulatory Board, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction: The concept of proton therapy was given first by the Robert R. Wilson in 1946. The first treatments were carried out with proton at Berkeley Radiation Laboratory in 1954. The world's first hospital-based proton therapy center was started in 1989 for ocular tumours at the Clatterbridge Centre for Oncology in the UK. At present, there are 73 particle therapy facilities which are operational and 15 under construction all over the world. Atomic Energy Regulatory Board (AERB), the organization which is responsible for enforcing provisions of radiation safety requirements in India in accordance with Atomic Energy Act, 1962 and Atomic Energy Radiation Protection Rules, 2004. AERB had received first application from the local supplier i.e. M/s IBA India Pvt Ltd., Chennai for obtaining no objection certificate (NOC) for their proton therapy accelerator model Proteus 235 having deliverable proton beam energies between 70 to 230 MeV for its to supply to M/s Apollo Hospitals Enterprises Pvt. Ltd, Chennai. Aim of this paper is to discuss the rationale ad process followed for the radiation safety assessment of the proton therapy accelerator facility and other safety review for issuance of various regulatory consents involved.
Materials and Methods: Though proton therapy facility is not new to the world but its first of its kind for India and the present safety code does not have stipulation on regulatory requirements for proton therapy facility. Accordingly, Chairman, AERB constituted Safety Committee for Hadron Therapy Facilities comprising experts from BARC, IGCAR, AERB and TMH for carrying out radiation safety review of Hadron Therapy Accelerator (for proton, carbon ion etc.), evaluation of radiation shielding for Hadron therapy facilities, to develop acceptance/quality assurance tests for such facilities for performance evaluation. Radiation safety and dosimetric parameters of Proton therapy Accelerators are different from that of medical linear accelerator. Hence for safety assessment of proton therapy accelerator, regulatory forms with relevant parameters for such facilities were developed after gathering information from manufacturer (M/s. IBA, Belgium) and literature available. Radiation safety assessment were completed by the above safety committee in four meetings after satisfaction from the submitted information and technical presentation by the manufacturer. Further, shielding calculation is very complex for proton therapy facilities due to its complex design. Analytical calculation method for the bunker overestimates at many locations depending upon the thickness of the walls/ceiling. Therefore, a working group comprising of Monte Carlo experts were formed for validation of the radiation shielding as proposed by the manufacturer for the user institution. This working group submitted its recommendation to the safety committee on the shielding adequacy of the layout plan.
Results and Discussion: Based on the safety review and recommendation of the safety committee, AERB has issued the site and layout approval to house 230 MeV Proteus 235 proton therapy accelerator and NOC to the M/s IBA India Pvt. Ltd, Chennai to supply this model to the M/s Apollo Enterprises Pvt. Ltd, Chennai. Construction of the facility is expected to be completed soon and further stage of regulatory review process will be completed once AERB receives application. Further, two more institutions have submitted their application for seeking regulatory clearances from AERB for establishing their proton therapy facilities. AERB is also in process of carrying out radiation safety review of proton therapy facilities of other two institutions.
Conclusion: AERB has followed rigorous review process for safety assessment of the proton therapy accelerator by constituting the safety committee comprising experts. As regulatory clearances for site & layout approval, import permission for proton therapy model Proteus 235 has already been granted by AERB, review of the performance test results will be reviewed by AERB for granting licence to operate the facility finally which will be the first proton therapy facility in the country.
| O-2: Effect of Deliverability Constraints on the IMPT Plan Quality|| |
Bojarajan Perumal, R. Vaitheeswaran1, Mohamad Nawaz Ahamad, Thajudeen Basha, Prajwal Kumar
Philips Radiation Oncology Systems, 1Philips ICAP Applications, Philips Innovation Campus, Bengaluru, Karnataka, India. E-mail: [email protected]
Purpose: The purpose of this study is to investigate the effect of deliverable constraints (Spot spacing and Minimum deliverable MU) in IMPT plan quality. Each IMPT delivery machine has their own limitations in terms of MU delivery just like LINAC's. Therefore after each optimization, there is a process called spot processing to be carried out in order to ensure that obtained MU's are deliverable by applying deliverable MU constraint. The spot processing can result in significant distortion in optimized dose distribution. In this paper the impact of applying deliverable MU constraint and the relation between spot spacing and deliverable MU constraint is studied.
Materials and Methods: Pinnacle IMPT non clinical version was used for IMPT Planning. Multiple treatment plans were generated for Prostate, Thorax, and H&N cases with varying spot spacing (2 –10 mm). Spot processing was done for all the plans and Dose Volume Histograms (DVH) were compared to evaluate OAR sparing and target dose homogeneity. DVH statistics were also compared before and after spot processing to study the impact of applying deliverable MU constraint to the optimizer with variable spot spacing.
Results and Discussion: In this paper, DVH for multiple plans were evaluated to study the effect of spot spacing and use of applying deliverable MU constraint to the optimizer. In our study, we found that, when spot spacing decreases, there is a significant improvement in plan homogeneity and OAR sparing. But many spots are observed with low intensity which may affect the plan robustness. OAR doses decreases when spot spacing increases. But also observed that significant difference in final dose distribution between pre and post processing of planned spots. This is because, when smaller spot spacing (2 mm and 3 mm) is used, number of spots increased dramatically which causes the MU of the each spots to be lesser than or close to the minimum deliverable MU constraint of the delivery system. Many of these spots are eliminated during post processing which causes deterioration in the final plan quality. This deterioration effect decreases above 4mm spot spacing roughly.
Conclusion: Out study demonstrate that, Spot spacing must be chosen to balance target dose homogeneity and OAR sparing. While decreased spot spacing increases target dose homogeneity, it also causes decrease in plan robustness as number of low intensity spots exists. This study shows that spot spacing of around 5 mm can be an optimal size to balance the homogeneity and OAR sparing to retain plan robustness. Also the effect of incorporating delivery MU constraint decreases when spot spacing is around 5 mm or above.
| O-3: Radiation Protection Aspects in a Medical Cyclotron Facility for Production of Positron Emitters|| |
Aruna Kaushik, Swatantra, Nitin Kumar, Sachin Sony, Puja Panwar, Pradeep Goswami, Sukhvir Singh, Anil K. Mishra
Institute of Nuclear Medicine and Allied Sciences, New Delhi, India. E-mail: [email protected]
Medical cyclotron dedicated for the production of positron emitting radioisotopes is operational at our Centre for the last ten years. It has an attached external beam facility that makes it unique in terms of research and radioisotope production. This is coupled to a radiochemistry laboratory wherein the positron emitting radioisotopes are labelled to pharmaceuticals to synthesize molecular imaging probes for Positron Emission Tomography (PET). Since the radioisotopes produced and handled in a medical cyclotron facility may be in solid, liquid and gaseous form, special precaution and care needs to be taken during production, synthesis and disposal of generated radioactive waste. Although the half-lives of positron emitters used for PET are short (few minutes to few hours), the amount of activity produced and handled during synthesis and dispensing is quite large. The objective of the present study is to address the radiation protection issues associated with production and synthesis of PET radiopharmaceuticals.
The medical cyclotron at our Centre (PETtrace System, M/s GE Medical Systems) is an unshielded type that accelerates negatively charged hydrogen ions (H-) to 16.5 MeV or negatively charged deuterium ions (D-) to 8.4 MeV energy. Positron emitting isotopes produced in the cyclotron are 18F, 11C, 13N and 15O. The synthesis of PET radiopharmaceuticals is carried out in hot laboratory that has chemistry modules housed in adequately shielded hot cells (M/s Comecer, Italy). The synthesis of PET radiopharmaceuticals may result in release of radioactivity in liquid or gaseous forms and generate solid waste. The radioactive gases from the synthesis modules are not released directly to the atmosphere but are compressed in the waste gas system till it decays to background level. It is subsequently released through exhaust system.
The radiation levels were monitored using area monitors (gamma and neutron) installed in the cyclotron vault, control console and beam extension facility. The gamma area monitor installed in the hot laboratory and the exhaust pipe was used to monitor the radiation levels during synthesis of PET radiopharmaceuticals. The exhaust pipe was also monitored by a gamma area monitor to measure the release of activity in air. The data from all the installed area monitors was displayed on the control console using ROTEM's Medismarts comprehensive monitoring system. Portable radiation survey cum contamination monitor ((Ramgene, M/s ROTEM, Israel) was used for contamination check and monitoring radiation levels at work benches, dustbins etc. The personnel were monitored using pocket dosimeters and thermoluminescent badges.
The gamma radiation levels in the vicinity of vault and in the hot laboratory ranged from 1 - 4 microsieverts per hour during isotope production. However, the radiation level during the transfer of 11C in the form of 11C labelled carbon dioxide from the cyclotron vault to the chemistry module was observed to increase to 10 – 20 microsieverts per hour. The radiation level near targets in the cyclotron vault ranged from 200 microsieverts per hour to 2 millisieverts per hour as monitored before every production. The havar foils removed from the target during maintenance were stored in the lead pit in the vault. However, the disposal of these foils need special attention and regulatory approval since these foils have long lived isotopes because of induced activity and the number of foils stored in the pit increase with time. The personnel involved in synthesis received whole body radiation dose of 2 – 3 microsieverts and wrist dose of 50 – 150 microsieverts per synthesis. The major contribution to personnel radiation dose was from dispensing of PET radiopharmaceuticals manually.
| O-4: Small Photon Field Dosimetry with Radiochromic Film Using an Indigenously Developed Program|| |
Ankur Mourya, Chhape Ram, Abhijit Mandal, Satyajit Pradhan, Uday P. Shahi, Sunil Choudhary, Lalit M. Aggarwal
Department of Radiotherapy and Radiation Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India. E-mail: [email protected]
Introduction: The measurement of the dose distributions for smalls fields are quite different from the reference conditions stated in the dosimetry protocols. Accurate dosimetry of small fields is complicated due to the electron disequilibrium, steep dose gradients, perturbation due to different density of the detector and the medium. Due to these challenges, the suitable detector for small field dosimetry should have high spatial resolution, small volume, linearity, and reproducibility, independent of energy and dose rate. Because of low energy dependence and high spatial resolution, Radiochromic Film is an appropriate dosimeter for dose measurement in small radiation fields having regions of high dose gradient. EBT3 film has been studied and accepted as a two dimensional detector especially for small Field dosimetry.
Objective: To investigate the capability of GafchromicEBT3 (External beam therapy, GafchromicTM) Film for dosimetry of small rectangular photon beam delivered with MLC and jaws.
Materials and Methods: EBT3 radiochromic film was used for measurement of dose. To calibrate Radiochromic film, we have cut the film into several small pieces and irradiated for various known doses with 6MV photon beam from a Varian Unique linear accelerator (Varian, Palo Alto, CA). The doses delivered to these cut films were 25, 50, 75, 100, 150, 200, 250, 300 cGy and film samples were handled according to AAPM TG 55 Report. Epson expression 11000XL desktop flatbed document scanner was used for film scanning that has maximum scanning spatial resolution of 1600 by 3200 dpi. Film were scanned in 48 bit RGB mode (16 bit per color) with resolution of 72 dpi (0.353 mm per pixel) and saved in tagged image file format (tiff). We have written a program in MATLAB 2013a (Math Works, Natick, MA) to analyze the scan film data by converting intensity into Dose. Red color channel of image was used and these images were imported in our program written in MATLAB. All film were read before irradiation and 48 hours after irradiation for most precise determination of netOD (net Optical density). Film dose response is usually expressed as measured netOD against the dose delivered to the film. However, when using film for dose measurement, dose is more conveniently plotted as a function of the measured netOD so that the data can be fitted to a curve (least square method). Scanner does not read OD directly, therefore, we defined following formula. netOD= log10 [(Iunex –Ibkg)/ (Iexp-Ibkg)]
Where Iunex = reading of ROI (region of interest) for unexposed film Iexp = reading of ROI for exposed film
Ibkg= zero light transmitted intensity
For measurement of doses from Jaws and MLC (Varian millennium 120), 6 films of sizes 6 x 6 cm2 were irradiated for 100MU, field sizes range from 1 x 1 cm2 to 5 x 5 cm2 within the solid water phantom at 5cm depth in SAD (SSD =95cm) setup. To read these films same procedure was used as used for film calibration. After that netOD was calculated and from this netOD, doses were calculated from our calibrated film data and doses obtained with gafchromic film was compared with doses obtained with other available dosimeters in the department.
Results and Discussion: With the help of film calibration data, doses for five different field sizes with MLC and Jaws were calculated. Dose for field sizes (1 x 1 cm2 to 5 x 5 cm2) defined by the jaws were 69.86, 83.31, 86.11, 88.12, 89.55 cGy and MLC were 70.91, 83.91, 86.96, 87.10, 90.41 cGy respectively. The variation in dose as compared to other dosimetric systems available in the department was within 3%. Percentage dose variation for MLC as compared to jaw were less than -1.48, -0.71, -0.98, 1.16, -0.95. It shows that with different field sizes dose delivered by MLC and jaws are same within 2% variation. Ionization chambers are usually used for calibration and beam measurements in conventional radiotherapy because of their high sensitivity, reproducibility and ease of use.
| O-5: Dual-Energy High-Rate X-Ray Computed Tomography Scanner Using a YAP-Photomultiplier Detector|| |
Tsukuru Sato, Eiichi Sato, Yasuyuki Oda, Yuichi Sato1, Satoshi Yamaguchi2, Osahiko Hagiwara3, Hiroshi Matsukiyo3, Toshiyuki Enomoto3, Manabu Watanabe3, Shinya Kusachi3
Department of Physics, Iwate Medical University, 1Department of Central Radiation, Iwate Medical University Hospital, 2Department of Radiology, School of Medicine, Iwate Medical University, Morioka, 3Department of Surgery, Toho University Ohashi Medical Center, Tokyo, Japan. E-mail: [email protected]
Introduction: To perform quasi-monochromatic X-ray computed tomography (CT), we have developed several energy-dispersive CT scanners using cadmium telluride detectors. However, it is not easy to improve image quality owing to low count rates. Therefore, we have developed high-count-rate detectors using a small photomultiplier tube (PMT), a PMT, a multipixel photon counter, and short-decay-time scintillators.
In our research, major objectives are as follows: to develop a dual-energy (DE) counter using three comparators, to increase the minimum count rate after penetrating the object, to perform DE-CT for fundamental studies using a detector consisting of a cerium-doped yttrium aluminum perovskite [YAP(Ce)] and a PMT, to improve both the spatial and energy resolutions, and to obtain two different energy tomograms simultaneously at the two energy ranges. Therefore, we constructed a DE-CT scanner with two different energy selectors operated at a tube voltage of 100 kV to carry out K-edge CT using iodine (I) and gadolinium (Gd) media.
Methods: To obtain two kinds of tomograms at two different X-ray energy ranges simultaneously, we have constructed the DE X-ray photon counter with a YAP-PMT detector, three comparators, and two microcomputers (MCs). X-ray photons are detected using the YAP-PMT detector, and the event pulses produced using amplifiers are sent to three comparators simultaneously to regulate three threshold energies of 33, 50 and 55 keV. Using this counter, the energy ranges are 33-55 and 50-100 keV; the maximum energy corresponds to the tube voltage. We performed DE-CT at a tube voltage of 100 kV.
Results and Discussion: Using a 0.5-mm-diam lead pinhole, two tomograms were obtained simultaneously at two energy ranges. K-edge CT using I and Gd media was carried out utilizing the two energy ranges. At a tube voltage of 100 kV, the count rate was approximately 100 kilocounts per second (kcps), and the minimum count rate after penetrating objects in DE-CT was regulated to approximately 10 kcps by the tube current.
| O-6: Pre-Processing of Breast Image for Peripheral Area Correction|| |
Hyemi Kim1, Haeng-hwa Lee1, Byungdu Jo1, Dohyeon Kim2, Donghoon Lee2, Hee-Joung Kim1,2
Departments of 1Radiological Science and 2Radiation Convergence Engineering, College of Health Science, Yonsei University, Seoul, Korea. E-mail: [email protected]
During breast image acquisition from the mammography, a compression paddle is used to make the breast thickness evenly. When the breast is compressed, the peripheral areas may not be fully compressed according to the breast thickness and composition. The inner regions of the breast are relatively thicker and denser than the peripheral areas, which can lead to overexposure to the periphery. Some images show low visibility of tissue structures in the breast peripheral areas due to the intensity change. It has a negative effect on diagnosis for breast cancer detection.
To improve image quality for analysis, we have proposed pre-processing technique based on distance transformation to enhance the visibility of peripheral areas. Since the results after image processing (segmentation, feature extraction) depend on the quality of the original image, the pre-processing is a necessary step.
As the initial step of the pre-processing, the breast region is separated from the background of the original image. In the case of MLO (Medio-lateral oblique) view image, the pectoral muscle is segmented by using the region-based segmentation method before pre-processing. Since the pectoral muscle shows a high intensity values in the image, it is removed at first and integrated after the image processing. The seeded region growing method initially specifies one seed pixel and extends the size of the region to neighboring pixels based on the intensity of the seed pixel. Also, only the pectoral muscle should be segmented by specifying the maximum distance from the seed pixel.
The peripheral areas of breast are determined by using the Otsu thresholding method to separate the peripheral and inner region based on the optimal threshold value. And the morphological processes are applied to peripheral areas to fill small holes and remove the small objects.
Before the correction of peripheral areas, the distance transform of breast region is performed by computing the distance from each pixel to the breast skin-line. This method aims to calculate the distance between each zero pixel and the nearest nonzero pixel in the binary images. For each pixel with the distance to the skin-line, the intensity of pixel is iteratively corrected by multiplying a propagation ratio. It is calculated as the ratio of the mean intensity of pixels at distances 1 and 2 steps from the furthest pixel of the peripheral areas to the skin-line. Finally, to evaluate the quality of processed images, the breast density is quantitatively calculated.
According to the results, the structure of breast tissues in the overexposed peripheral areas was well observed. By improving the intensity of the peripheral areas, we obtained a profile of uniform intensity from the inner region of breast to the skin-line. The pixel values of peripheral areas were normalized without losing information and weighted to reduce the intensity distribution variation. The histogram also showed that the low intensity parts of the peripheral areas were significantly reduced.
In addition, after applying the peripheral area correction, we applied the contrast enhancement method to calculate the breast density more accurately. Compared to the original image, the breast density calculated from the processed image obtained similar results with the actual density of breast image. These results suggest that appropriate pre-processing techniques are useful for improving image quality and more accurate density assessment.
In this study, the pre-processing technique based on distance transformation was used to overcome the problem of overexposed peripheral areas in the breast images. The results demonstrated that peripheral area correction method combined with contrast enhancement improved the visualization of the breast peripheral areas and the accuracy of the breast density assessment can be further improved.
| O-7: Mammography Imaging Study Using Synchrotronradiation|| |
Reena Sharma1, J. Shramika1, S. D. Sharma1,2, D. Datta1,2
1Radiological Physics and Advisory Division, Bhabha Atomic Research Center, 2Homi Bhabha National Institute, Mumbai, Maharashtra, India. E-mail: [email protected]
Recent advancements of medical x-ray imaging techniques are based on differential absorption of x-ray intensity. However, the technology has its own limitation due to subject contrast in soft tissues. To overcome such limitations, an emerging technology called X-ray Phase Contrast Imaging (XPCI) algorithm has been employed in many medical imaging areas including mammography. Further XPCI has shown the potential improvement with respect to visibility contrast while examining soft tissues found within the breast. XPCI utilizes the refraction of x-rays at the boundary defined by two different density regions. This refracted and the direct waves propagate a finite distance and interfere due to a path difference to produce bright and dark fringes. This is manifested in terms of edge enhancement along the boundary of interest. Complex index of refraction is represented by n=1-δ–iß, where δ is the refractive index decrement that is responsible for the phase shift, and ß is the absorption index. Phase retrieval seems impossible with conventional x-ray sources (e.g conventional mammography x-rays) due to their low spatial coherence.
The aim of the study was to establish the suitability of XPCI for its diagnostic capability in terms of quantitative image quality parameter called contrast to noise ratio (CNR) as it plays an important role in deciding the image quality of any x-ray based imaging systems.
Present study utilizes the monochromatic 20 keV synchrotron x-ray with high degree of spatial coherence available at imaging beam line-4 (BL-4) of the synchrotron facility, Indus-II. Indus II is a 2.5 GeV, 300 mA third generation synchrotron radiation source located at Raja Ramanna Centre of Advanced Technology, Indore, India. We have carried out all the experiments using imaging camera system of Photonic Science VHR-1 which contains a 1:2 fibre-optic plate coated with Gadox Scintillator and high resolution charged couple devices (pixels 4007 x 2678, pixel size 4.5 μm and field of view 18 mm x 12 mm).
Microcalcifications (MCs) in the breast are considered as indirect signs of pathological process and detecting these on mammograms are difficult task due to its small size which is less than 1 mm. In conventional mammography, aluminium (Al) is often used as a substitute material for calcification simulation and in the same line we have fabricated a microcalcification phantom using 'Al' with diameter of 5 mm and different thickness ranging from 50 -500 μm. These 'Al' discs were sandwiched between two polymethyl methacrylate (PMMA) sheets each having 1 mm thickness. Images of each 'Al' disc were acquired and CNR was measured for every disc using equation 1.
where, MPVsignal is the mean signal pixel value, MPVbkg is the mean background pixel value, SDsignal is the standard deviation (SD) in the signal area, and SDbkg is the standard deviations in the background area. CNR was calculated for each 'Al' disc image using Image J software (Image J -IJ 1.46).
Results of the present study show that measured CNR values for 'Al' discs with thicknesses 50, 100, 170, 400 and 500 μm are 6.24, 14.2, 21.5, 44.9, and 56.7 respectively. For 100 μm thick 'Al' disc, measured CNR values along with (PMMA) attenuator of thicknesses 1 to 8 mm are found to be 14, 13.4, 12.7, 11, 10.7, 10.4, 10.1, and 8.16 respectively. This condition was simulated to show how CNR for 100 micron 'Al' discs decreases with respect to its depth position in a soft tissue substitute material (e.g PMMA). Also edge line profile investigated for 100 μm thick 'Al' disc shows the improvement in visibility contrast at the boundary of disc under XPCI technique.
| O-8: Triple-Energy High-Rate X-Ray Computed Tomography Scanner Using a Cadmium Telluride Detector|| |
Eiichi Sato, Yasuyuki Oda, Yuichi Sato1, Satoshi Yamaguchi2, Osahiko Hagiwara3, Hiroshi Matsukiyo3, Toshiyuki Enomoto3, Manabu Watanabe3, Shinya Kusachi3
Department of Physics, Iwate Medical University, 1Department of Central Radiation, Iwate Medical University Hospital, 2Department of Radiology, School of Medicine, Iwate Medical University, Morioka, 3Department of Surgery, Toho University Ohashi Medical Center, Tokyo, Japan. E-mail: [email protected]
Introduction: Without pileup of the event pulses, the maximum count rate of a high-energy-resolution cadmium telluride (CdTe) detector is approximately 5 kilocounts per second (kcps). In energy-dispersive computed tomography (ED-CT), the photon count rate substantially decreases while penetrating the objects. The image quality improves with increasing minimum count rate after penetrating the object, and the incident count rate to the object should be increased with increases in the object thickness to maintain the minimum count rate for CT.
In our research, major objectives are as follows: to develop a triple-energy (TE) counter using three comparators, to keep the minimum count rate after penetrating the object, to perform TE-CT for fundamental studies using a readily available CdTe detector, and to obtain three different energy tomograms simultaneously at the three energy ranges. Therefore, we constructed a TE-CT scanner with three comparators operated at a tube voltage of 100 kV to carry out K-edge CT using iodine (I) and gadolinium (Gd) media.
Methods: To obtain three kinds of tomograms at three different X-ray energy ranges simultaneously, we have constructed a TE X-ray photon counter with a CdTe detector and three sets of comparators and microcomputers (MCs). X-ray photons are detected using the CdTe detector, and the event pulses produced using amplifiers are sent to three comparators simultaneously to regulate three threshold energies of 20, 33 and 50 keV. Using this counter, the energy ranges are 20-33, 33-50 and 50-100 keV; the maximum energy corresponds to the tube voltage. We performed TE-CT at a tube voltage of 100 kV.
Results and Discussion: Using a 0.5-mm-diam lead pinhole, three tomograms were obtained simultaneously at three energy ranges. K-edge CT using I and Gd media was carried out utilizing two energy ranges of 33-50 and 50-100 keV, respectively. At a tube voltage of 100 kV and a current of 60 A, the count rate was 15.2 kilocounts per second (kcps), and the minimum count rates after penetrating objects in TE-CT were regulated to approximately 2 kcps by the tube current.
| O-9: High-Sensitivity Near-Infrared-Ray Computed Tomography Scanner|| |
Yuichi Sato, Eiichi Sato1, Yasuyuki Oda1, Osahiko Hagiwara2, Hiroshi Matsukiyo2, Toshiyuki Enomoto2, Manabu Watanabe2, Shinya Kusachi2
Department of Central Radiation, School of Medicine, Iwate Medical University, 1Department of Physics, Iwate Medical University, Morioka, 2Department of Surgery, Toho University Ohashi Medical Center, Tokyo, Japan. E-mail: [email protected]
Introduction: Recently, we have developed several energy-dispersive X-ray computed tomography (CT) scanners and performed K-edge imaging using iodine and gadolinium media. Using these scanners, blood vessels are observed at high contrasts. Subsequently, a 950-nm near-infrared-ray (NIR) CT scanner has been developed to observe hemoglobins in biomedical objects. However, it was difficult to penetrate the objects, since the NIRs in the living-body (LB) window range from 700 to 900 nm.
In our research, major objectives are follows: to develop an NIR-CT, to increase detection sensitivity, to produce LB-window NIRs, and to improve spatial resolutions. Therefore, we developed an 850-nm NIR-CT scanner and imaged biomedical objects.
Methods: In the NIR-CT, NIR rays are produced from a light-emitting diode (LED), and the penetrating rays are detected using an NIR phototransistor (PT) in conjunction with a long graphite collimator. The wavelengths of maximum LED intensity and high PT sensitivity are 850 and 940 nm, respectively. The photocurrents flowing through the PT are converted into voltages using an emitter-follower circuit, and the NIR sensitivity increases with increasing resistance between the emitter and the ground. The output voltages are sent to a personal computer through an analog digital converter. The projection curves for tomography are obtained by repeated linear scans and rotations of the object. The object rotates on the turn table, and the NIR scanning is conducted in both directions of its movement.
Results and Discussion: We performed NIR-CT using a set of LED and PT driven in the LB-window NIR range. The NIR photons easily penetrate a transparent object at a small incident angle, and the photons reflect around the objects at a large incident angle to the object. In addition, the photons also refracted, and only penetrating photons should be detected using a small-diam long collimator for the PT.
The pixel dimensions of the reconstructed CT image were 0.5 × 0.5 mm2 because the scan step was 0.5 mm. However, the original spatial resolution was primarily determined by both the collimator diameter (1.0 mm) and length (10 mm), and the spatial resolutions were approximately 2 × 2 mm2.
| O-10: High Resolution CT Lung Patient Skin Dose Measurement Using Metal Oxide Semiconductor Field Effect Transistor|| |
A. Saravana Kumar, K. N. Govindarajan, B. Devanand1, N. Elango1, R. Rajakumar1
PSG Centre of Radiological Physics, PSG Institute of Medical Sciences Research, 1Department of Radiology, PSG Institute of Medical Sciences Research, Coimbatore, Tamil Nadu, India. E-mail: [email protected]
Introduction: High-resolution computed tomography (HRCT) is computed tomography (CT) with high resolution. It is used in the diagnosis of various health problems, though most frequently for lung disease. It involves the use of special computed tomography scanning techniques to assess the lung parenchyma. The advent of MDCT has resulted in improved spatial resolution and faster scans acquisitions. Consequently, MDCT has become a more widely used diagnostic procedure, responsible for a greater proportion of medical Radiation exposure to patients. Although CT represents 11% of all radiographic examinations, it accounts for 67% of medically induced radiation exposure. A judicial practice of CT procedure has to be ensured for patient's safety. An understanding of patient CT radiation doses requires the assessment of organ and effective dose in patients undergoing CT procedures. The universal method for measuring organ and effective radiation doses is dose estimate from the CTDI or DLP, which is both used as readily accessible dose indicators of radiation dose in CT procedures. In this research study, patient skin dose were measured and compared with the console CTDIv. Using these values, correlation can be found between CTDI vol and skin dose, the later can be used to infer the order of CTDIvol values.
Objective: The objective of our study was to measure radiation skin dose during HRCT lung using a novel dosimeter system and compared with the displayed console value.
Materials and Methods: A solid-state metal oxide semiconductor field effect transistor (MOSFET) was used to obtain real-time skin dose for HRCT lung procedures in 128 slice Siemens Somatom definition edge scanner. 50 HRCT lung cases have been selected, then two Mosfet sensors namely S1D and S2D were used and both have been placed on the patient with different points without affecting examination.
Results and Discussion: The console CT dose indices have been noted and the range and mean value of CTDIv is 4.8 mGy to 12.7 mGy, and 10.22 mGy respectively. The dose response to the Mosfet probes to exposure ranging and mean values are 2.51 cGy to 8.54 cGy, 4.8 cGy for S1D, and 2.83 cGy to 9.21 cGy, 4.7 cGy for S2D respectively. The sample measured data have been presented in [Table 1]. From this result, we observed that there is correlation between the measured CT skin doses and theoretically calculated console value.
|Table 1: Comparison of console computed tomography dose index volume and measured skin dose using metal oxide semiconductor field effect transistor technology|
Click here to view
Conclusion: On whole, this research work gives the substantial overview of HRCT lung practice in our hospital. From this study, it is recommended that it is very essential to justify CT procedures in advance and once the choice for CT scan is taken, it is compulsory to adopt the ALARA and dose reduction principle strictly. MOSFET technology can be used for protocol development in the rapidly changing MDCT scanner environment in which organ dose data are extremely limited. The data of such study is essential so as to reduce the time considerably for optimization of machine output and average patient doses.
| O-11: Knowledge Based Planning for Stereotactic Radiosurgery: Standardisation of Volumetric Modulated Arc Therapy Based Frameless Stereotactic Technique Using a Multidimensional Ensemble Mapping|| |
Sarkar Biplab, Ganesh Tharmar, Satheeshkumar Anbazhagan, Kaur Harpreet, Jassal Kanan, Giri Upendra Kumar, R. Sashikumar, Saneg Kirshnankutty, S. P. Jeen, Munshi Anushhel, Mohanti Bidhu Kalyan
Department of Radiation Oncology, Fortis Memorial Research Institute, Gurgaon, Haryana, India. E-mail: [email protected]
Aim: Knowledge based planning (KBP) is an emerging technique in a radiation therapy planning. It helps to standardise the radiotherapy planning as variations in knowledge and experience of the planner can lead to large differences in the quality of radiation therapy treatment plans. This may compromise the gains achieved through modern technologies such as IMRT or VMAT. This study is attributed to standardisation of brain SRS/SRT plans in our institution. The aim of this study is standardisation of the treatment plans by minimization of the influence of individual's skill and knowledge, based on a very large library of treatment plans. Further effort will be made to reduce the planning time.
Materials and Methods: 171 SRS/SRT patients treated in our clinic were considered in this study. An ensemble library was established using first 120 patients, further the KBP algorithm was validated for 29 library patients and tested for 51 new patients. Ensemble library was categorised against 8 different parameters (1) PTV dose coverage challenged by presence of organ at risk (OAR) or not (2) Prescription dose (3) Number of PTVs (4) laterality (left/right) (5) tumour volume (6) shortest distance between OAR and PTV (7) centre to centre distance between OARs and PTV (8) lateral dimension of external contour (brain). Further, on arrival of a new patient most appropriate library plan was chosen on the basis of above categorisation using an ensemble mapping technique. Further for new patient knowledge based planning (KBP) was created by associating most appropriate library plan with all parameters unchanged to the default isocentre. Optimization and dose calculation was carried out in MONACO with no or very minimal changes in the optimization constrain and arc length. Another independent treatment plan (IP) was generated by an experience medical physicist for comparison. IP and KBP were evaluated for PTV dose coverage (V98%), Paddick conformity index (PCI), dose spillage of (volume of 50% and 20% isodose lines; I50%, I20%) and OAR doses.
Result: For 43.3% (52 out of 120) patients it was observed that PTV dose was not challenged by the presence of any OAR. Validation result for ensemble mapping technique shows that for an OAR challenged PTV dose patient it is appropriately picking up the library plan. Independent plan (IP) was better than the knowledge based plans (KBP) in PTV coverage and dose conformity. PTV volume receiving 98% prescription dose (V98%) was 98.7 ± 1.1% and 97.5 ± 1.3% for IP and KBP respectively. For OAR challenged PTV's conformity was slightly high in IP (0.712) than KB plans (0.693). PTV V98% and PCI were not statistically different between two sets. If collimator angle optimization is not done for the OAR unchallenged cases PTV conformity is higher than KBP in IP and variation was statistically significant (p<0.04). Collimator angle optimization equalise the Conformity between IP and KBP. For the largest prescription dose group (12Gy in 1#, 64 patients) brainstem 0.5 cc Volume exhibit a mean dose of 873.1 ± 134.2 cGy and 854.5 ± 122.4 cGy for IP and KBP respectively. All other OAR doses were comparable between IP and KBP. MU difference was very nominal with IP shows a mean excess MU of 67.3 (3.7%) over KBP. IP requires on average 3.5 optimization/dose calculation which is about 3.5-5 hrs, where KBP does not require more than 1.5 runs (1.5-2) hrs.
Conclusion: KBP plans validation result indicate multidimensional ensemble mapping mechanism can pick up the library plan accurately. KBP plans, although marginally inferior in the dosimetric quality, they fulfil all the required clinical condition and dose constraints. KBP plans save a considerable planning time and almost independent of the treatment planner skill and knowledge. KBP works well with Monte Carlo planning system like MONACO.
| O-12: Monte Carlo Modelling of Indigenously Developed Medical Linear Accelerator|| |
P. K. Dixit, Subhalaxmi Mishra1, T. Palani Selvam1, Sanket S. Yavalkar2, D. D. Deshpande3
Radiological Safety Division, Atomic Energy Regulatory Board, 1Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, 2Department of Technology Innovation, Society for Applied Microwave Electronics Engineering and Research, 3Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction and Objective: The objective of the present study is to simulate the 6 MV LINAC (model Siddharth), indigenously developed by SAMEER (Society for Applied Microwave Electronics Engineering and Research) using the BEAMnrc user-code of the EGSnrc Monte Carlo Code system. This study also includes identification of initial electron parameters and comparison of calculated dose distributions with the measured data.
Materials and Methods: Different components of the LINAC such as target, primary collimator, flattening filter, monitor chamber, mirror, and secondary collimator were modelled using the BEAMnrc user-code as per the technical design data provided by the manufacturer. In order to identify the initial electron parameters, phase space data at Source-to-Surface Distance (SSD) of 100 cm for the field size of 10 x 10 cm2 was scored for different initial electron parameters. Using the phase space data, lateral dose distribution at 10 cm depth in a water phantom of dimensions 50 x 50 x 50 cm3 was calculated using the DOSXYZnrc user-code. The investigation revealed that dose distribution corresponding to the initial electron energy 6.2 MeV with a Gaussian spread (FWHM of 1 mm) matched with the measured data. Further simulations involving various filed sizes (5 x 5 cm2 – 25 x 25 cm2) utilized the above electron parameters. Dose measurements in water phantom were carried out by PTW MP3 Water Scanning System and ionization chamber (Semiflex 0.125 cm3). These measurements were performed with 1 mm resolution for both PDD curves and beam profiles.
Result and Discussion: The depth and lateral dose distributions for all the investigated field sizes agree to the measured data as well as with international reference data within about 2%. PDD for field size 10 x 10 cm2 is shown Figure 1. Penumbra, field sizes, beam flatness and beam symmetry are found to be within the tolerance values. The calculated and the measured dose profiles for different field sizes are shown in Figure 2. The study suggests that Monte Carlo model of the Siddharth LINAC is accurate.
|Figure 1: Comparison of measured and Monte Carlo calculated Percentage Depth Dose (%) variation with distance along the central axis for Field size of 10 x 10 cm2|
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|Figure 2: Comparison of measured and Monte Carlo calculated Relative dose variation with Y-distance for Field size of ranging from 5 x 5 cm2 to 25 x 25 cm2|
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| O-13: Impact of Preclinical PET Geometrical Arrangement on Performance Parameters|| |
Kajal Aggarwal, Fredéric Boisson, David Brasse
Hubert Curien Pluridisciplinary Institute, University of Strasbourg, Strasbourg, France. E-mail: [email protected]
Introduction: Preclinical Positron Emission Tomography (PET) is a nuclear imaging modality used to image animal models of human disease. Several groups proposed different geometrical arrangements, to push current limits of spatial resolution and system detection efficiency. Due to the different design choices each configuration has its own advantages and limitations.
While pixelated scintillators provide an advantage of improved spatial resolution, the depth of the crystal creates an imbalance between the detection efficiency and the spatial resolution. This arrangement leads to parallax error due to radially longer crystals, thus degrading the spatial resolution. This tradeoff can be overcome by introducing multi layers of crystals coupled in the radial direction. A geometrical arrangement having axially oriented pixelated crystals is also a promising concept to avoid parallax error. Similarly, other geometrical arrangements such as scanners with monolithic crystal slabs have their own benefits and drawbacks.
Objective: The objective of this study is to investigate the impact of four different preclinical PET scanner geometries using the figure of merit proposed by the National Electrical Manufacturers Association (NEMA) NU 4 - 2008 standards through Monte-Carlo simulations.
Materials and Methods: We propose to investigate four different geometries including a), pixelated crystal matrix coupled to Silicon Photomultiplier (SiPM) detector, b), dual layer of crystal matrices, c), crystal axially oriented with dual side readout and d), monolithic crystal slabs. The transverse field of views of the four systems are ranging from 5 to 6 cm according to the arrangement of the different PET modules. The average axial extent is set to 10 cm to cover the whole body of a mouse.
Result and Discussion: The figures of merit investigated according to NEMA procedure include scatter event rate, Noise Equivalent Count Rate (NECR), detection efficiency and spatial resolution. The preliminary results obtained using the GATE simulation platform show that the axial PET arrangement has the highest sensitivity along with higher NECR values, followed by dual layer arrangement and scanner employing monolithic scintillator, as predicted theoretically.
Those results will be compared to a state of the art preclinical scanner installed in our facility.
| O-14: Development of F18-FDG PET/CT Database of Lung Masses for Imaging Research|| |
Mukesh Kumar, A. K. Pandey, Kartik Saroha, C. S. Bal, Rakesh Kumar
Department of Nuclear Medicine, AIIMS, New Delhi, India. E-mail: [email protected]
Introduction: Image processing algorithms have potential to assist in lesion (e.g. nodule) detection on PET/CT studies and to assess the stability or change in size of lesion on serial PET/CT studies. Comparison and evaluation of image processing techniques against each other require common data sets and standardized methods for evaluation. Creating a computer based tumor classifier system that can classify malignant versus benign lungs mass, inflammation versus malignancy, and responder versus non-responder to chemotherapy based on lungs PET/CT images can be of immense value. In order to validate the accuracy of such classifier we need large image database of the patients.
Objectives: The aim of this study was to develop the F18-FDG PET/CT images database of lung masses for imaging research.
Materials and Methods: Two hundred sixty four lungs cancer patients who underwent F18-FDG PET/CT scan from November 2015 to December 2016 for detection of early treatment response, for measurement of response to neo-adjuvant chemotherapy, chemo-radiotherapy or novel biologic therapies were included in this study. Their general information (patient' s history, gender, age, no of Chemo/RT, identification number, final report issued by our department) and clinical history, biopsy reports of the lungs mass if available were recorded. Whole body F18-FDG PET/CT scans of all 264 selected patients (250 patients having lung cancer and 14 patients having normal lungs) were exported in DICOM format.
The PET and CT image series of all patients were reviewed in MeVisLab. The PET/CT fused axial section image which shows the maximum dimension of lung tumor was selected as representative image of lung mass of the patient. These images were also included in the database so that this database can be used as clinical teaching tool for postgraduate students.
The database was developed using Microsoft Access on Windows 7 Home Basic Copyright © 2009 Microsoft Corporation and Microsoft Access installed on the processor Intel® Core™ i3-2120 CPU @ 3.30 GHz, 2.0GB RAM and 64-bit operating system on the computer (Hewlett-Packard Company).
Results and Discussion: The database has information of 264 patients (adenocarcinoma: 34 %, NSCLC: 9%, SCC: 27%, and normal lungs: 5%) and some other details are given in [Table 1]. The demographic information, clinical history, lungs PET and CT images of each patient can be accessed with the help of mouse and push buttons available on the user interface of the database Figure 1. This image database can be used for standardization, evaluation and comparison of many digital image processing methods such as image enhancement, image registration, image fusion, and texture analysis etc. This image database can also be used as for teaching postgraduate students as it consists of the PET/CT images of different types of lung cancer at one place. Three types of PET/CT lung mass (Adenocarcinoma, NSCLC and SCC) and PET/CT normal lungs images can be accessed through this database for demonstration during the lecture. For example, a list of all PET/CT images of adenocarcinoma can be accessed and displayed to explain to the postgraduate students regarding the spatial pattern of the tumor appearance on the PET/CT images. Our future plan is to determine the size of the tumor on PET/CT images, and assign a label to each image based on the location, size, and stage of the disease. This will make the image database more valuable while teaching postgraduate nuclear medicine students.
|Figure 1: When user press Option button then Microsoft office Security Options appears. Now user can select to enable the content and then select frmImageTable to view the PET/CT images. frmImagesTable have command button for navigation (Home, Previous and Next)|
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| O-15: Optimisation of the Moving Average Filter Parameter for Processing 99MTC-MDP-BONE Sxscan Image|| |
Anil Kumar Pandey, Chandan Singh Bisht, Averilicia Passah, Ravi Kant Gupta, Chetan Patel, Chandrashekhar Bal, Rakesh Kumar
Department of Nuclear Medicine, All India Institute of Medical sciences, New Delhi, India. E-mail: [email protected]
Introduction: 99mTc- Methylene diphosphonate (MDP) bone scan is corrupted with noise during image acquisition. Moving average filter can recover the original image signal from its noise-corrupted version. However, the user needs an optimized value of window size to obtain the best result. In this study we have optimised the value of window size for 99mTc-Methylene diphosphonate bone scan for best possible image quality.
Objective: The aim of the study was to find the optimum value of window size for mean filter to be applied on 99mTc-MDP bone scan for best possible image quality.
Materials and Methods: Seventy six 99mTc- MDP whole body bone scan (32 normal and 44 abnormal, total counts: 739,000 to 1783, 855 per image) images were included in this study. A matlab script was written to process these images using moving average filter with window sizes 3, 5, 7, 9, 11, 13 and 15 pixel widths. The experiment was conducted on personal computer having a 3.30 GHz i3-2120 CPU, 2 GB RAM memory, and 64-bit Windows operating system. The image quality of processed images (N = 456) were evaluated subjectively by two nuclear medicine physician to select the best image.
Results and Discussion: Nuclear medicine physicians preferred original images 73.61% times, and processed image with window size 3-pixel widths 26.39% times. Approximately 26% of whole body 99mTc- MDP bone scans required noise removal operation, and in those cases, the optimized window size of moving average filter for processing 99mTc- MDP bone scans was found to be 3-pixel widths.
| O-16: Radiation Dose from 18F-FDG PET/CT Procedures: Influence of Specific CT Model and Protocols|| |
Oluwabamise Adeleye, Naven Chetty
School of Chemistry and Physics, University of KwaZulu-Natal, Pietermaritzburg, South Africa. E-mail: [email protected]
Integrated PET/CT imaging has proven to be a valuable tool for the diagnosis, staging, and monitoring of therapy response of a broad range of malignancies due to the combined metabolic and morphological information provided. The increasing use of this imaging modality in the management of tubercular lesions has raised concerns regarding the associated radiation exposure, because of the additional exposure from CT acquisition with the internally administered radiopharmaceuticals. This work aimed to study the effects of CT model and study protocols on the overall radiation dose from a PET/CT scan.
Two PET/CT systems and five CT exposure protocols routinely applied for clinical patients in PET/CT imaging were retrospectively evaluated. CT doses were calculated using the CT-Expo dosimetry software, while doses from the PET component were estimated applying the International Commission on Radiological Protection (ICRP) 106 dose coefficients. Effective dose was calculated using the ICRP 103 and for comparison the ICRP 60 tissue weighting factors. The total effective dose for each system was compared in terms of percentages and the difference in CT component contribution to the total dose for all protocols were determined using two-sample t-test with p < 0.05 considered as significant.
Effective dose ranged from 8.0-24.05 mSv for the system I and 8.35-26.85 mSv for system II, resulting in differences of 4.3%-15% for the Low-dose scan and 4.1%-11% for standard dose scans. The contribution of CT component to the total dose was between 32-77% for the system I and 35-79% for system II; however, the contributions were not significantly different (p > 0.05) for all protocols.
Although the overall radiation dose was similar with both types of system, the observed variation in CT contribution represents a requisite pedestal on the need for a nation-wide dose assessment for further optimization of the imaging procedure to maximize benefit to patients.
| O-17: Analysis Of Therapeutic Effectiveness by Generation of Three Alpha Particles in Proton-Boron Fusion Reaction Based on Monte Carlo Simulation Code|| |
Sunmi Kim, Han-Back Shin, Moo-Sub Kim, Do-Kun Yoon, Tae Suk Suh
Department of Biomedical Engineering, College of Medicine, Research Institute of Biomedical Engineering, Catholic University of Korea, Seoul, Korea. E-mail: [email protected]
Introduction: In previous reports, proton-boron fusion therapy (PBFT) induces tumor cell death through three alpha particles of triggered by one proton based on proton-boron fusion reaction. A major advantage of proton irradiation is a characteristic distribution of dose with depth. The dose deposited increases at first very slowly with depth and then very sharply near the end of a range, before dropping to almost zero. Protons deposit energy far more selectively than X-rays, improving long-term local control of the tumor, lower probability of damage to healthy tissue, low risk of complications, and the chance for rapid recovery after therapy. Theoretically, PBFT is a novel and desirable therapy for malignant tumors with advantages over conventional proton therapy and boron-neutron capture therapy (BNCT). In the case of BNCT, after the compound containing boron is accumulated at the tumor site, only one alpha particle resulting from the reaction between the epi-thermal neutron and the boron causes tumor cell death. If it could be matched the deposition of three alpha particles in the tumor regions and the proton's maximum dose point (Bragg peak), the therapy results can be more effective than in BNCT. However, a more quantitative evaluation for PBFT is needed for clinical application.
Objectives: The purpose of this research is to analysis the effectiveness by generation of three alpha particles in proton-boron fusion therapy (PBFT) based on a Monte Carlo simulation code.
Materials and Methods: Dosimetry using Monte Carlo simulation is a suitable technique to describe the energy deposition by alpha particle. A proton beam relevant to Bragg-peak was simulated using a Monte Carlo simulation code. After computed tomography (CT) scanning of a virtual water phantom including air cavities, the acquired CT images were converted as the simulation source code. We set boron uptake regions (BURs) in the simulated water phantom to achieve proton-boron fusion reaction. A rectangular 20(W) × 20(D) × 8.5(H) cm3 water phantom (Water region density: 1 g/cm3) with air cavities was used. The 1 phantom was comprised of two air cavities, each with a different size (2 × 20 × 2 cm3, 4 × 20 × 4 cm3) and location (6 cm, 11 cm away from the phantom surface). The proton emission in the simulation was directed toward the phantom. On the simulations, a boron concentration in the tumor and the adjacent healthy tissue to the tumor were incorporated to the virtual phantom, resulting in a concentration ratio of healthy tissue:tumor of 1:5. This ratio is approximately the concentration ratio found in some pharmacokinectic experimental studies of boron carries, mainly for the boronophenylalanine compound, known as BPA-fructose.
Results and Discussion: Results show clearly that three alpha particles affected the energy deposition. Thus, high therapy efficiency can be achieved by using smaller flux than that of conventional proton therapy or BNCT. We exploited the p + 11B → 3α reaction to generate high-LET alpha particles with a proton beam. The results described the intrinsic strong points of PBFT. Although additional study needs to further verify the effectiveness of PBFT, we confirmed the greater therapeutic effectiveness of proton boron fusion reaction by generation of alpha particles over either conventional proton therapy or BNCT. We will proceed with further study on verification and quantification to move towards implementation of clinical treatment.
| O-18: Commissioning and Validation of Commercial Deformable Image Registration Software|| |
Jamema Swamidas, Reena Phurailatpam, Siji N. Paul, Kishore Joshi, D. D. Deshpande1
Department of Radiation Oncology, Advanced Centre for Treatment Research and Education in Cancer, 1Department of Medical Physics, Tata Memorial Centre, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction: Validation/commissioning of Deformable Image Registration (DIR) is complex and still evolving. The objective of this study is to report the results of the validation tests carried out as part of commissioning of the commercially procured DIR algorithm before clinical implementation for adaptive contouring.
Materials and Methods: The DIR software tested was SmartAdapt® in Eclipse™ treatment planning system v13.6 (Varian Medical Systems Inc., Palo Alto, CA). The tests were carried out using physical and virtual phantoms in addition to the clinical test images. Physical Phantoms: Five phantoms made in-house with various known deformations with landmark points were used. The known deformations were ranged from simple to complex as shown in Figure 1. Contours were delineated for each phantom set which were propagated to the registered images. Synthetic/virtual phantoms: A set of 10 virtual phantoms were used (https://sites.google.com/site/dirphantoms/virtual-phantom-download). For each phantom, the magnitude of displacement in lateral, AP and SI direction were evaluated for various organs such as brainstem, spinal cord, mandible, parotids and external contours were compared with the ground truth. The results were obtained by comparing the DVF of the specified ROI to the ground-truth DVF. Clinical images for contour propagation: Four clinical sites namely, brain (n=5), HN (n=9), cervix (n=18) and prostate (23) patients were validated. A planning CT and a subsequent CT taken after 2-3 weeks (CT/CBCT), were considered retrospectively. OARs were manually delineated by a radiation oncologist (RO), followed by DIR and propagation of contours, which were compared with the RO drawn contours. Evaluation: Dice similarity co-efficient (DSC), shift in centre of mass (COM) and Hausdorff distances Hf95% and Hfavg were evaluated (3D slicer v 22.214.171.124).
Result: Physical phantoms: Mean (SD) DSC, Hf 95% (mm), Hfavg (mm) and COM of all the phantoms 1-5 were, 0.84 (0.2), 5.1 (7.4) mm, 1.6 (2.2) mm, 1.6 (0.2) mm respectively. Phantom 5 had the largest deformation as compared to phantom 1-4, and hence had resulted in suboptimal indices, 0.5 (0.8) vs 0.9 (0.03), 18.3 (3.5) vs 1.8 (0.4), 5.7 (1.2) vs 0.64 (0.1) and 14.2 (1.8) vs 0.83 (0.3) mm.
Virtual phantoms: Several commercial DIR algorithms were investigated in this project, and our results (Institution -18) were consistent for all the ROIs. More specifically, our results were in good agreement with that of the institution -9 which also had used a similar algorithm as ours.
Clinical images: The contours propagated for brain patients resulted in a high DSC score (0.91 (0.04)) as shown in Figure 2, as compared to other sites (HN: 0.84, prostate: 0.81 and cervix 0.77). A similar trend was seen in other indices too.
|Figure 2: CBCT registered with CT of a brain cancer patient with post operative edema. Green: DIR generated contour, Yellow: RO drawn contour|
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In HN, the DSC was in the range of 0.81-0.87, with mandible scoring the highest with 0.87 (0.03). The less deformed structures like eyes and thyroid scored a mean (SD) DSC of 0.84 (0.06) as compared to parotids with relatively large deformations scoring 0.81 (0.03).
In cervix and prostate, DIR resulted in better results, when the small bladder was registered with large bladder and not vice versa. In other words the expansion of the bladder was handled well by DIR than the shrinkage. When the change in the bladder volume was about 50-150cc, the propagated contours were acceptable, however when the change in the bladder volume is of the order of 200-300cc, the contour propagation was unacceptable. Unlike bladder, rectum is more complex due to the presence of gas pocket and the complexity in shape.
Conclusion: DIR algorithm investigated works well in sites such as brain, HN, prostate and cervix for adaptive contouring purpose. However, the accuracy of the propagated contours is limited for some situations involving complex deformations that include large change in the volume of bladder, shape change in recto-sigmoid. Visual validation of the propagated contours is recommended for clinical implementation.
| O-19: Development of Real Time On-Line Quality Assurance Device for Afterloading HDR Brachytherapy|| |
Department of Radiotherapy, Madurai Medical College, Govt. Rajaji Hospital, Madurai, Tamil Nadu, India. E-mail: [email protected]
Introduction: Accurate delivery of dose in HDR brachytherapy depends on the positioning accuracy of the Ir-192 source at the proper dwell position inside the applicator. Incorrect implementation of either of these parameters can potentially lead to insufficient tumour control and high dose being delivered to the incorrect treatment volume. Consequently, accurate positioning verification of the HDR source is a fundamental part of quality assurance (QA) procedure. A number of methods have been used to check the positional accuracy like mechanical rulers, autoradiography and video cameras. However, these methods are time consuming for a routine QA program and they cannot furnish information on the actual source locations, So these techniques may not enough to verify the accuracy of the HDR source position. I have developed a new real time On-line quality assurance device for testing and verification of source positioning and dwell time for HDR brachytherapy.
Objective: The objective of this study was to develop in-house software based real time On-line quality assurance device that can autonomously perform the source positioning and dwell time of HDR brachytherapy.
Materials and Methods: The in-house HDR QA device consisted of light tight box, PMMA block, a fluorescent screen, a webcamera and in-house software. The webcamera was placed on the top of the light tight box. The HDR source transferring tube was connected in the bottom of the light tight box. Ir-192 source would be loaded was put on the fluorescent screen and a sheet of PMMA was placed below the fluorescent screen. When the Ir-192 radioactive source moving on the fluorescent screen the gamma photons converted into light photon by the fluorescent screen. The visible lights indicates the real time positioning of the source. The visible light signal was recorded by the web camera, which was placed in the top of the light tight box. The web camera video signals was fed into a computer in-house software. In the software automatically calculate to determine the distance between successive dwell positions. Step intervals ranging from 5mm to 25mm were set while 5mm interval. The differences between two dwell positions were compared with the assigned values. For timing measurements, individual images from the video signal were similarly processed to identify the location of the source. Source actual dwell time was calculated from number of images, which indicated the source at the corresponding position. The total transit time was measured by subtracting source stationary time from total dwell time. Simultaneously Gafchromic EBT film autoradiography was also used for comparing the positioning accuracy.
Results and Discussion: In source positioning accuracy test, for assigned intervals of 5mm, 10mm, 15mm, 20mm and 25mm, average measured interval by the in-house software were 4.9mm, 9.9mm,14.9mm, 19.9mm and 24.5mm respectively. The result from autoradiography was also compared. The system achieved a time resolution of 10 ms and determined the dwell time to be 1.05 sec, with a standard deviation of 0.03 sec. The system was able to successfully perform positioning and timing QA measurements automatically and the movement of the source can be seen in the computer screen in the control console area during the procedure. It can provide fast and precise positional verification of a treatment plan. Advantages of our technique is its fast and precise positional verification, ability to visually check source treatment for safety checks and eliminating confusion distance between physical end of the catheter and center of the source. We can have the softcopy & hardcopy results for the further evaluation and comparison.
| O-20: DOSIMETRIC IMPACT OF TWO METHODS OF POINT A DEFINITION IN HIGH DOSE RATE INTRACAVITARY BRACHYTHERAPY FOR CERVICAL CANCERS|| |
Arpana Siwach, Shivakumar Gudi1, Kevezo Zango Chuzho, Yogesh Ghadi, Jamema Swamidas, D. D. Deshpande, Umesh Mahantshetty1
Departments of Medical Physics and 1Radiation Oncology, Tata Memorial Centre, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction: Intracavitary brachytherapy is an integral component of curative treatment for locally advanced cervical cancers. For many decades point A has been the surrogate for target definition and dose prescription in cervical brachytherapy and its still the most widely used method. Because of the geometric uncertainties related to the point A defined by the Manchester System (1953), some modifications to the definition has been suggested by American Brachytherapy Society (ABS) in 2011, which is adopted by the recently published ICRU 89 (2016). The dosimetric impact of such modifications needs to be evaluated.
Purpose: To investigate the dosimetric variations between two different methods of Point A definition and the impact of such variations on the ICRU surrogate points for rectum and bladder as well as 3D Dose volume parameters of these structures.
Materials and Methods: Twenty one patients who underwent CT based HDR Intracavitary brachytherapy using the standard stainless steel or CT/MR compatible Fletcher-Suit applicators (Nucletron- Elekta, Netherlands) were included in the study. Treatment planning was done using the “Oncentra” treatment planning system (version 4.3, Elekta) which works on TG43 calculation algorithm. Two treatment plans were generated each normalized to point A as per two different definitions: (i) The Revised Manchester point A which is defined 2 cm superior to the flange (surrogate for the external cervical os) and 2 cm lateral from the center of tandem and (ii) ABS /ICRU-89 point A definition which defines the point A from the midpoint of line joining the center of ovoid channels and then superiorly (R+2) cm along the tandem, where R is the radius of the ovoid and 2 cm lateral to it. Standard loading pattern was used for both the plans. Doses to point A in both the plans, ICRU Bladder and rectal points and 3D dose volume parameters 2cc for bladder and rectum were documented and compared using paired t test.
Results and Discussions: The plans normalized to point A defined according to the ICRU89/ABS recommendations, recorded higher doses at the point A defined by the Manchester system, bladder and rectal dose parameters. The mean differences standard deviations between the doses recorded at right and left Point A in two plans were 11.1 11.4 cGy (p<0.005) and 10.7 11.1cGy (p<0.005) respectively. Similarly the mean dose differences to ICRU Bladder point, ICRU Rectum point, Bladder 2cc and Rectum 2cc were 6.1 7.7cGy (p=0.002), 6.6 7.4 cGy (p=0.001), 9.7 10.1cGy (p=0.000) and 6.2 6.9 cGy (p=0.001) respectively. Also, the volume receiving prescribed dose and Total Reference Air Kerma (TRAK) values were higher (2.3% and 1.6% respectively) in the plans normalized to point A as defined by the ABS.
The results of the study demonstrated small but statistically significant differences in dosimetric parameters between the plans generated as per two definitions of point A when current commercially available Fletcher-Suit applicators were used. These differences appear to be small and unlikely to have clinical impact, however, this needs to be validated in different patient cohort and other applicator types.
| O-21: A Simple Novel Technique for Ring Applicator Catheter Reconstruction On CT and MRI 3D Image Based Brachytherapy Planning for Cervical Cancer|| |
Devaraju Sampathirao, S. V. Jamema, Yogesh G. Ghadi, Umesh Mahantshetty, Deepak Deshpande
Department of Radiation Oncology and Medical Physics, Tata Memorial Hospital, Parel, Mumbai, Maharashtra, India. E-mail: [email protected]
Background and Objective: Catheter reconstruction is a vital step in the BT planning process. This has been further challenged by successful implementation of CT/MR Image based BT in cervical cancer. MR compatible applicators catheter reconstruction is complex and based on water dummies. The annulation and orientation of the ring applicator poses a major challenge for reconstruction. With an aim to make the reconstruction simpler, yet accurate, we undertook this study and form the basis of this abstract.
Materials and Methods: CT/MR compatible ring applicator (Make: Nucletron, Model: 101.036, Ring Tube) of 26 mm diameter used. After defining the origin along the axis of the tandem and surface of the ring, central tandem reconstruction was done by selecting index number 3 (TPS: Oncentra, v4.3). Loading of the active dwell positions in central tandem was done and in the transverse orientation (view) the isodose line passing through the dummy at the level of the ring was utilized to perform the manual ring catheter reconstruction. The reconstruction performed by this method was verified using the auto radiograph and compared with the dwell positions obtained during applicator commissioning.
Results and Discussion: It was observed that the planned and delivered active dwell positions within the tolerance of +1 mm. The novel technique described above was faster and less error prone. This is a time efficient method as compared to manual reconstruction; however the limitation of this method is that the source path in the ring may not be perfectly circular as the isodose lines. Commissioning of the applicators is mandatory before the clinical use.
Conclusion: A simple novel and time efficient technique for accurate reconstruction of the ring applicator catheter seems feasible and should be the preferred method in busy BT workload environment.
| O-22: Current Status and Technical Challenges of Secondary Calibration System for RAKR of 192IR HDR Brachytherapy Source in Japan|| |
S. Kawamura, T. Yamada1, T. Mikamoto2, J. Itami3
Faculty of Fukuoka Medical Technology, Teikyo University, 2Japan Radioisotope Association, 3Department of Radiation Oncology, National Cancer Center Hospital, Tokyo, 1Kindai University Atomic Energy Research Institute, Osaka, Japan. E-mail: [email protected]
Introduction: The national standard of 192Ir brachytherapy source in terms of reference air kerma rate (RAKR) had been prepared by National Metrology Institute of Japan (NMIJ) in 2015. Following this, the secondary calibration service system of 192Ir for limited medical users had been started by Japan Radioisotope Association that is secondary calibration laboratory in Japan. We experimentally carried out the calibration of well-type dosimeter using primary standard source provided by NMIJ.
Objectives: The purpose of this study is to appear the problems and challenges of this calibration system. We make it a goal to complete the calibration system for all medical users by 2018.
Materials and Methods: 35 well-type dosimeters which have collected for calibration from medical user were calibrated in terms of RAKR. Indicated air kerma rate of each dosimeter had compared with RAKR obtained by secondary standard dosimeter, which was calibrated by primary standard source Iuser is current obtain by well-type dosimeter of user, ktp is air temperature and pressure correction factor. kion,user is ion recombination correction factor of user dosimeter. Sk,JRIA is air kerma rate measured by secondary standard dosimeter of JRIA. kT is correction factor of reduced radioactivity.
Results: The average and standard deviation of the calibration coefficient of each dosimeter Nsk, JRIA (Gyh-1A-1) were evaluated. We have successfully carried out calibration of well-type dosimeters.
Conclusion: We evaluated the calibration coefficient of well-type dosimeter of medical user which used MicroSelectron. We will plan to expand other equipment user by 2018.
Kessler C, Kurosawa T, Mikamoto T. Comparison BIPM.RI(I)-K8 of high dose-rate Ir-192 brachytherapy standards for reference air kerma rate of the NMIJ and the BIPM. Metrologia 2016;53 Suppl 6001:10.
| O-23: Analysis of Doses to Organs at Risk While Defining the Point a from the Manchester System and the ICRU 89 Recommendations|| |
X. Sidonia Valas, S. Purnima, T. Godwin Paul Das, K. Thayalan, G. Bharanidharan1
Medical Physics Division, Dr. Kamakshi Memorial Hospital, 1Department of Medical Physics, Anna University, Chennai, Tamil Nadu, India. E-mail: [email protected]
Introduction: Point A is the major critical surrogate for dose specification of Intracavitary Brachytherapy. The original definition of Point A, define by Tod and Meredith (1938) intended to indicate the point where uterine artery crosses the ureter and is defined from the surface of the ovoids, which were not feasible to locate using the imaging modalities at that time. The Modified Manchester System by them changed the location of point A to be derived from the bottom of the tandem sources or the stopper of the tandem at the os level. The recent ICRU 89 recommendations, guides to locate the Point A from the surface of the ovoids which could be easily adopted by today's imaging modalities.
Aim: This study attempts to investigate the dosimetric impact of Point A on the OAR doses of bladder, rectum and sigmoid defined by the Manchester System and the ICRU 89 recommendation.
Materials and Methods: Fifty High Dose Rate (HDR) plans of patients treated for carcinoma cervix by Intracavitory Brachytherapy post external beam radiotherapy at our centre were chosen retrospectively for this study.
The patients were implanted with the standard Fletcher Tandem-Ovoid applicator under general anesthesia and the CT images were obtained for planning. Two sets of plans were created by specifying dose to Point A s; one derived from the Manchester System i.e., from the os level/stopper of the tandem and the other one by the ICRU 89 recommendations i.e., from the surface of the ovoids or by drawing a central intersection line at the centre of ovoid sources and including the radium of the ovoid used. The volume of pear shape of the prescription dose and 0.1 cc and 2 cc of bladder, rectum and sigmoid were compared.
Results and Discussion: The point A is defined from the two systems get located in two different dose gradient regions. The volume of the pear shape is higher for ICRU 89 point A. This gives a consequent increase of the dose received by all the OARs and maximum of 14% increase of dose is found in 2 cc of bladder volume. It is also noted that the patients with early diseases have a better anatomy and thus a comparatively a good application of brachytherapy. In such cases, there is no much difference in the location of Point A s derived from the two methods.
| O-24: 3-Dimensional Verification of Pear-Shaped Dose Distributions of HDR Intracavitary Brachytherapy Deliveries Using Normoxic Polymer Gel Dosimetry: A Comparison Between Gel Dosimetry and TPS Results|| |
Devi Nand Singh
Department of Radiation Oncology, Command Hospital, Kolkata, West Bengal, India. E-mail: [email protected]
Introduction: The gel dosimeters are tissue equivalent materials used for relative dose measurement of modern radiotherapy deliveries such as IMRT, VMAT, SRS, SRT and HDR Brachytherapy. MRI and X-ray computed tomography based HDR brachytherapy treatment planning and volumetric dose calculations are being used at many radiotherapy clinics. A variety of dosimeters are commercially available for volumetric dose verification of EBRT deliveries but there is a lack of such dosimetry tool for HDR brachytherapy.
Objective: The purpose of this study was to verify the pear-shaped dose distributions of HDR intracavitary brachytherapy deliveries using normoxic polymer gel dosimeter and compared the results with that of TPS calculations.
Materials and Methods: N-isopropyl acrylamide (NIPAM) based normoxic polymer gel dosimeter was prepared inhouse on the bench-top of radiotherapy department following methods described elsewhere. For dose-response linearity study, 30 mL gel-filled vials were irradiated from 1-15 Gy dose. 50 patients diagnosed with carcinoma cervix with FIGO staging (IIA, IIB, IIIB) were included in this study. These patients were subjected to weekly HDR Intracavitary Brachytherapy followed by external beam radiation therapy (EBRT) to pelvis. Brachytherapy planning was performed on a treatment planning software to deliver the prescribed dose to different anatomical reference positions. Similar plans were executed onto a self-designed gel phantom filled with NIPAM gel loaded with applicator and ovoids. The imaging of the irradiated gel phantom was performed using X-ray CT modality of PET-CT scanner. The DICOM images were analysed using modified MATLAB software. The pear-shaped dose distributions derived with 1 mm resolution were compared with TPS calculations. Statistical analysis was performed with help of Epi Info (TM) 3.5.3 which is a trademark of the Centers for Disease Control and Prevention.
Results and Discussion : The dose response was linear from 1 to 15 Gy (p< 0.001) with dose sensitivity of 0.46 ± 0.05 HU/Gy. The results of this study showed that there was good agreement between the gel dosimetry measurements and TPS calculations. Brachytherapy gel dosimetry provides dose distributions in all 3 dimensions, which enables us to define the dose distributions in any plane with high resolution (~1mm). It has been reported in many studies that 2D point dosimetry based on ICRU 38 may either over or under estimating the actual dose to the anterior rectal wall. [2,3] To meet out these challenges, ABS and GEC-ESTRO has recommended for 3D imaged based brachytherapy practices.[4,5] The results of this study will be helpful for pre-treatment verification of three-dimensional dose distributions of typical HDR brachytherapy deliveries.
Senden RJ, De Jean P, McAuley KB, Schreiner LJ. Polymer gel dosimeters with reduced toxicity: A preliminary investigation of the NMR and optical dose-response using different monomers. Phys Med Biol 2006;51:3301-14.
Ling CC, Schell MC, Working KR, Jentzsch K, Harisiadis L, Carabell S, et al . CT-assisted assessment of bladder and rectum dose in gynecological implants. Int J Radiat Oncol Biol Phys 1987;13:1577-82.
Schoeppel SL, LaVigne ML, Martel MK, McShan DL, Fraass BA, Roberts JA, et al. Three-dimensional treatment planning of intracavitary gynecologic implants: Analysis of ten cases and implications for dose specification. Int J Radiat Oncol Biol Phys 1994;28:277-83.
Viswanathan AN, Thomadsen B, American Brachytherapy Society Cervical Cancer Recommendations Committee, American Brachytherapy Society. American brachytherapy society consensus guidelines for locally advanced carcinoma of the cervix. Part I: General principles. Brachytherapy 2012;11:33-46.
Viswanathan AN, Beriwal S, De Los Santos JF, Demanes DJ, Gaffney D, Hansen J, et al. American brachytherapy society consensus guidelines for locally advanced carcinoma of the cervix. Part II: High-dose-rate brachytherapy. Brachytherapy 2012;11:47-52.
| O-25: Monte Carlo Study of Water-Equivalence of Various Solid Phantom Materials for 131CS, 125I and 103PD Low Energy Brachytherapy Sources|| |
Subhalaxmi Mishra, T. Palani Selvam
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction: Experimental brachytherapy dosimetry is a challenge in terms of positional accuracy due to steep gradients in dose and dose rate, low photon energies, and spectral changes with distance from the source. Solid phantom materials can be easily machined to accommodate the source and detector in a precise position, facilitating an accurate measurement and reproducibility in source-detector geometry. Several solid phantom materials are being used for the dosimetric measurements of brachytherapy sources. However, for low energy brachytherapy sources (less than 50 keV), the dose distributions are highly sensitive to phantom compositions due to the predominance of photoelectric effect.
Objective: The aim of this work is to study the water-equivalence of various solid phantom materials for low energy brachytherapy sources such as 131Cs, 125I and 103Pd using Monte Carlo-based EGSnrc code system.
Materials and Methods: The brachytherapy sources included in this study are 125I (model Selectseed), 103Pd (model IRA1) and 131Cs (Isoray model Cs-1). The solid phantom materials investigated are PMMA, polystyrene, solid water, virtual water, RW1, RW3, A150 and WE210. The detectors investigated in this study are diamond, Li2B4O7 and LiF.
Phantom scatter correction at distance (r) along the transverse axis of the source, kphan (r ), can be calculated at a brachytherapy beam quality Q for solid-state detector by using the following relation:
kphan (r )=[D det,Q(r )/D det,phan,Q(r )]
Where, D det,Q(r ) and D det,phan,Q(r ) are the absorbed dose to a given detector material in liquid water and in the solid phantom at a distance r along the transverse axis of the photon emitting brachytherapy source of beam quality Q, respectively. Note that, kphan (r )=1 means the phantom material is water-equivalent.
In the Monte Carlo calculation of absorbed dose to detectors in water and in solid phantom materials were based on the FLURZnrc user-code of EGSnrc code system. The source is positioned at the centre of a 40 cm diameter and 40 cm height cylindrical phantoms (liquid water and solid phantoms). The photon fluence spectrum is scored in 0.5 mm thick and 0.5 mm high detector materials at different positions varying from 0.5 cm to 10 cm along the transverse axis of the source. The fluence spectrum is converted to collision kerma to water and collision kerma to detector materials by using the mass-energy absorption coefficients of water and detector, respectively. Up to 109 photon histories are simulated. The statistical uncertainties on the calculated values of kphan (r ) is less than 0.5%.
Results and Discussion: The study shows that for a given detector kphan (r ) depends on r for the investigated phantom materials, but the degree of deviation from unity depends on the type of solid phantom and the brachytherapy source. For all the detectors, kphan (r ) decreases with r for polystyrene, PMMA, RW1 and RW3 phantom materials and increases with r for the remaining phantom materials. kphan (r) values are calculated for diamond, Li2B4O7 and LiF detectors for 125I, 103Pd and 131Cs brachytherapy sources, respectively.
Phantoms such as solid water, virtual water and WE210 are water-equivalent at short distances (less than 3 cm) for all the investigated detectors and brachytherapy sources. However, as the distances increases these phantom materials tend towards non water-equivalence (at 10 cm, kphan (r ) value is about 20 % larger than unity). Remaining phantoms such as PMMA, RW1, RW3 and PMMA showed significant kphan (r ) values (about 80 % lesser than unity at 10 cm distance). The solid phantom materials such as solid water, virtual water and WE210 can be treated as water-equivalent phantoms at short distances (less than 3 cm) for the dosimetric measurements of low energy brachytherapy sources.
| O-26: Validation of Heterogeneous Algorithm Using EBT2 Stack Film with Metal and Shielded Applicator in HDR Brachytherapy|| |
Mourougan Sinnatamby, Vivekanandan Nagarajan1, Sathyanarayana Reddy K2, Gunaseelan Karunanidhi
Department of Radiotherapy, Regional Cancer Centre, JIPMER, Puducherry, 2Regional Cancer Centre, JIPMER and Head, Oncology, Mahatma Gandhi Medical College and Research Institute, Puducherry, 1Department of Medical Physics, Cancer Institute, Chennai, Tamil Nadu, India. E-mail: [email protected]
Introduction: Worldwide the importance of prior independent verification of treatment plan has been recognized in HDR brachytherapy. The measurement of planned dose distributions poses a challenging task due to large dose ranges, high dose gradients, and small spatial scales. A number of experimental and Monte Carlo (MC) studies have been reported in literature representing the influence of inhomogeneity in brachytherapy treatments and the shielding effect created by the applicators. It is essential that QA needs to be in line with progress as recommended in TG-186 for HDR brachytherapy treatment planning and delivery to ensure an appropriate level of dosimetric accuracy and quality.
Objectives: To validate the model based dose calculation algorithm using EBT2 stack film with metal and shielded applicator in HDR brachytherapy.
Materials and Methods: Three different experimental setup with the applicators used in Varian Medical System, GammamediX plus viz., interstitial metal catheters, ring applicator with ring cap and rectal retractor, vaginal mould partially shielded applicator used in conjunction with multiple EBT2 Gafchromic film to study the planar fluence pattern calculated using Varian Medical System, AcurosTM BV (Grid Based Boltzmann solver) heterogeneity algorithm. EBT2 Gafchromic stack film can be read with Epson Expression 10000XL flatbed scanner to validate AcurosTM BV in HDR brachytherapy. Film QA Pro 2015 software used to validate the different criteria set for gamma analysis. The IBM SPSS version 21 software used for the data analysis and paired t-test tool showed a comparison of the mean difference between paired data.
Results and Discussion: The point doses calculated with AcurosTM BV using a virtual phantom created in the TPS, which agreed with MC based calculation mostly within 2%. Based on the recommendations given in IAEA TRS 430 report, the commissioning of brachytherapy TPS, a 5% dose /2 mm distance criterion for gamma function was studied and the results showed 95% passing rate. Whereas in this study the gamma pass percentage was higher than the conventional TG-43 based calculation. To verify this dose with heterogeneity algorithm with gamma pass criteria of 5% and 1 mm, a gamma pass rate of 96% shown. In reviewing the literature, the common standard set for gamma criteria in brachytherapy was 5% and 2 mm. The EBT2 film stacked one after another without air gap to enable to verify the fluence at a different plane, however, this method was a modified method of a study conducted by Palmer et al, where in validation done by placing the film at regular interval. In the Interstitial Metal Catheters setup, analysis of plane by plane showed maximum gamma difference as 1.45%, DD -0.817%, DTA 1.38% and all showed no statistically significant difference. In titanium ring applicator with the acetal ring cap and rectal retractor setup. The sagittal fluence and frontal fluence were generated in single exposure simultaneously and analyzed. On comparing one plane with another plane maximum gamma difference noted in frontal and sagittal as 4.0% and 3.82%, DD showed 2.72% and 2.25% difference, DTA showed 3.72% and 2.71% difference in the frontal and sagittal plane. In the vaginal mould partially shielded setup, stack film was placed both in the shielded as well as in the unshielded area. The shielded area showed no dose to compare which was confirmed with TPS calculation. The unshielded portion of the applicator where films are stacked showed dose and was analyzed plane by plane, the maximum difference in Gamma showed -5.28%, DD with 2.95% and DTA with 3.71%. Thus methods used provide a comprehensive verification for validation of the heterogeneity algorithm and stack film dosimetry can be a useful 3D tool for QA program in HDR brachytherapy.
| O-27: Radiation Shielding Evaluation of Model Layout Plan for Remote Afterloading Iridium/Cobalt Source Brachytherapy Treatment Room: Theoretical Calculation|| |
Mahendra More, S. P. Srivastav
Kiran Multi Super Speciality Hospital and Research Center, Surat, Gujarat, India. E-mail: [email protected]
Introduction: Radiotherapy continues to be the main stay of cancer management globally and more than 60% patients receives radiotherapy for the treatment of cancer, and of these 5–15% patients are treated by brachytherapy as a single or combined modality. Brachytherapy continues to be the most conformal treatment modality with very high dose delivery to the core of target volume and excellent dose fall off, to spare the organs at risk (OARs) with least integral dose. It continues to have radiobiological superiority and it has the ability to boost the target volume with judicious choice of target volume to achieve better outcome.
Objectives: The aim of this study is to evaluate the model layout plan for remote afterloading Iridium (Ir-192) and Cobalt (Co-60) source brachytherapy treatment room design and the factors affecting these designs and to optimize protection of patient, staff and public.
Materials and Methods: Use of Iridium-192 and Cobalt-60 source in High Dose Rate (HDR) brachytherapy unit has come for discussion in recent publications. For these units treatment room or vault must be designed and constructed with due considerations in shielding design, equipment type, workload, use factor, shielding material, available space, ALARA principle, Regulatory constraints etc.
Model layout room plan for Ir-192 HDR room with 10 Ci Source and Co-60 HDR room with 2.0 Ci source were studied. The workload was calculated on basis of 4.0 hours of machine ON time per week.
WORK LOAD (W) = Activity of source X Max. weekly ON Time of the machine for treatment of patients X Specific Gamma Ray Constant = cGy/wk at 1 metre.
W (Ir-192) = 20 cGy/wk at 1 metre
W (Co-60) = 10 cGy/wk at 1 metre
We further calculated the dose rate at a certain distance from the source due to primary, scattered and leakage radiation and from it one could derive how many TVL's we need to bring the radiation levels to the dose constraints OR annual dose limits to occupational workers or public specified in safety reports.
This institute has constructed room for Cobalt-60 unit and will install remote after loading brachytherapy unit. The existing room is to conform to radiological safety requirements of Cobalt-60 brachytherapy unit. This study presents theoretical approach and complete details about design of HDR brachytherapy treatment room and evaluation of model plans in view of radiation safety around the installation.
Results and Discussion: The calculated wall thicknesses are appropriate for annual exposure dose limits for public area as well as for occupational worker. The thickness of primary wall 0.45 m is adequate as there is no occupancy towards these walls and the thickness of wall towards CT simulator room is increased to 0.50 m so as to reduce the exposure.
Design dose limits should also be considered while planning treatment room for radiation facility as specified in radiation safety code.
| O-28: Probabilistic Safety Assessment of Remote Afterloading High Dose Rate Brachytherapy Facility|| |
Rajib Lochan Sha, D. B. Nagrale1, Alok Pandey, Pankaj Tandon, A. U. Sonawane
Radilogical Safety Division, Atomic Energy Regulatory Board, 1Nuclear Safety Analysis Division, Atomic Energy Regulatory Board, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction: All kinds of medical radiation facility may lead to potential exposure of patients. However, there may be more probability for serious accidents in radiotherapy than in other medical practices, because of the high doses and high activity sources used. In this study, the safety evaluation for radiotherapy RAL HDR Brachytherapy facility is carried out considering the fatality due to radiation overexposure.
Objective: Probabilistic safety assessment (PSA) is essentially used for safety evaluation of radiation facilities to reduce the radiological risk from the possible potential exposures to the patients, occupational workers and the member of public.
Materials and Methods: The approaches and methodologies to assess the safety are very much matured in case of nuclear facilities with comparison to non-nuclear facility. The present PSA study is undertaken for RAL HDR Brachytherapy equipment “GammaMed Plus iX” utilise Ir-192 gamma irradiation source for the purpose of delivering treatment of cancer patient. In this treatment a pre-determined dose is delivered to specific portion of patient, such that the intended therapeutic result is obtained. Considering the serious deterministic effect and fatality due to radiation over exposure as a risk measure, the application of PSA to safety evaluation of GammaMed Plus iX RAL HDR Brachytherapy facility is presented in this paper. The safety assessment is carried out taking all possible failures in the design and safety system/interlock of the facility. Two models such as event tree and fault tree are used to present the logical structures in a manner suited for quantitative analysis.
Results and Discussion: The frequency (per year) of getting inadvertent high dose to patient is found as 6.09E-7 from the probabilistic safety assessment of GammaMed Plus iX RAL HDR Brachytherapy facility. The results indicate that frequency of fatal exposure is below the acceptance criteria. The overall risk to the overexposure can be reduced by providing the adequate training to the operator and improving the good safety culture in the medical institution, without major modification in the design and safety system/interlock of existing GammaMed Plus iX RAL HDR Brachytherapy facility. However, additional safety locking mechanism for the source should be provided to ensure the immobilisation of the source while not used. The source locking will be used manually to lock the source after the use of the HDR brachytherapy unit. Due to presence of the source locking wire the source will not be able to come out of the safe parking position.
Conclusion: The probabilistic safety assessment of GammaMed Plus iX RAL HDR Brachytherapy facility indicates that the frequency of inadvertent high dose (for a patient) of RAL HDR Brachytherapy facility is less than 1E-6 per year. The international guidelines for risk from food irradiation facility is mentioned as 1E-6 per year as per ICRP-76.
Acknowledgment: We are thankful to the technical staff of M/s. Varian Medical System, International India Pvt. Ltd, Supplier of GammaMed Plus iX RAL HDR Brachytherapy facility for providing the necessary informations in detail of GammaMed Plus iX for our PSA study.
| O-29: Pre-Treatment Verification of Advanced Radiotherapy Using Elekta Linac Parameters Tracked in Real-Time|| |
Nur Shaheera Midi, Hafiz Mohd Zin
Oncology and Radiological Sciences Cluster, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Penang, Malaysia. E-mail: [email protected]
Pre-treatment verification of IMRT ensures accurate delivery of the treatment planned. The current practice is to use a dosimetry system to verify the dose delivered by the linac. Any errors undetected during treatment delivery may jeopardise the cancer cure and increase the severity of radiation side effects. However, dose measurement may take time to perform and is prone to error if the detector is not calibrated correctly. The approach may be inconvenient for a busy radiotherapy treatment facility due to high patient load and low staff ratio. Varian linac records treatment delivery parameters as log files that is accessible to the end users. However, Elekta linac does not provide such log file but has a function to log the delivery parameters in real-time using the service graphing function available from the linac control computer. The study has developed an algorithm to analyse the real-time data using Matlab (MathWorks, Natick, MA). The algorithm measures any errors in the treatment parameters and reconstructs the parameters into dose given to cancer patient during radiotherapy. The technique simplifies the conventional processes using a detector, but at the same time efficiently ensure that the radiation delivered to cancer patient is accurate. The algorithm has been tested to verify the accuracy of radiotherapy treatment for head and neck cancer patients in Advanced Medical and Dental Institute, Universiti Sains Malaysia. The results agree well with the standard measurements using radiation detector but significantly reduce the time required to perform the check. Additionally, the algorithm can also be used to analyse detailed performance of radiotherapy treatment parameters such as MLC positions and other treatment delivery parameters such as gantry and collimator angle. Acknowledgement: This work is funded by Fundamental Research Grant Scheme, Ministry of Education Malaysia, 203/CIPPT/6771383.
| O-30: Dosimetric Comparision of Coplanar and Non-Coplanar Intensity Modulated Radiation Therapy Planning for Esophageal Carcinoma|| |
Vinay Desai, B. Shwetha, M. Ravikumar, K. M. Ganesh, S. Sathiyan, C. Varatharaj
Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India. E-mail: [email protected]
Introduction: The curative potential advantage of radiation therapy in the management of esophagus cancer is greatly enhanced by the use of IMRT. The success of IMRT requires the high radiation dose delivery to the tumor, while sparing the surrounding normal tissues. The aim of this study is to compare the feasibility of coplanar and non-coplanar Intensity Modulated Radiotherapy (IMRT) plans to improve the treatment.
Objective: To compare the dosimetric impact of coplanar and non-coplanar IMRT plans for esophageal carcinoma and to optimize the treatment approach for the esophageal cancer.
Materials and Methods: In this study CT images of 20 esophageal carcinoma patients, who had undergone the IMRT treatment, were considered. Six of them had cervical and upper thoracic tumors and were grouped together as 'Group 1', and the remaining fourteen patients had middle and lower thoracic section tumors and they were grouped separately as 'Group 2' and 'Group 3' (seven patients each). The contouring and treatment planning was performed in the Eclipse treatment planning system (TPS). The dose to 95% tumor volume, dose received by heart, lung and spinal cord were calculated using the DVH from Eclipse TPS. The dose distribution of PTV was assessed by evaluating the maximum dose (Dmax), mean dose (Dmax) and minimum dose (Dmin). To evaluate the plan quality with respect to the dose delivered to the tumor, the Conformity number (CN) conformity index (CI) and heterogeneity index (HI) were computed.
Results: For Group-1, Group-2 and Group-3 patients mean dose of coplanar plan were much better than those in non-coplanar plan, but the mean dose gradient in non coplanar plan didn't show much significant difference. For group-2 patients the non coplanar IMRT plan could reduce the dose to the lung tissue, thus reducing the probability of radiation pneumonia to esophageal cancer patients. The drawback of non-coplanar IMRT is that, it resulted in higher dose to the heart and spinal cord compared to the coplanar plan.
Discussion: In this study, for all groups of patients it was found that coplanar IMRT plan produced higher mean dose to PTV than non-coplanar IMRT plan. Maximum dose to the PTV is found to increase in the non-coplanar plans when compared to coplanar plans. Although HI of both the plans was almost equal to one, coplanar IMRT plans showed better HI values. Mean lung dose (MLD) is found to be reduced in non-coplanar IMRT plans when compared to coplanar plans as lung can be spared due to non-coplanar entry of the beam through the body. Radiation pneumonitis is the main factor to limit clinical therapeutic effect and the goal was to reduce the irradiation to the lung. Hence in this study it was found that the non-coplanar IMRT plans could have been the effective tool to reduce the irradiation of lung. However as shown for non-coplanar plans, reduction in the irradiation of lung may also reduce the conformality of the plan. It was also found from this study that non-coplanar IMRT plans increased the dose to the heart while reducing dose to the lung. For Group-2 and Group-3 patients the dose to the heart was considered as the constraint and it was found that there was a significant increase in the mean dose of heart and spinal cord in non-coplanar IMRT plan. The drawback of non-coplanar IMRT is that, although within tolerance limits, it delivers a higher dose to the heart and spinal cord compared to the coplanar plan.
| O-31: Lung and Breast Cancer Risk Estimates Following Involved-Site Radiation Therapy for Supradiaphragmatic Hodgkin'S Disease in Female Patients|| |
M. Mazonakis, E. Lyraraki1, J. Damilakis
Department of Medical Physics, Faculty of Medicine, University of Crete, 1Department of Radiotherapy and Oncology, University Hospital of Iraklion, Heraklion, Greece. E-mail: [email protected]
Introduction: The Hodgkin's disease (HD) is a highly curable malignant disease which often affects young adults. Radiation therapy plays a major role in the management of this malignancy. However, the therapeutic irradiation with both extended and involved fields may be associated with an increased second cancer risk. A new concept, known as involved-site radiotherapy (ISRT), was recently introduced to restrict the treatment volumes. Limited information has been published about the probability for the appearance of secondary malignancies following ISRT for HD.
Objectives: The purpose of the current study was to estimate the lung and breast cancer risks in female patients undergoing ISRT for supradiaphragmatic HD.
Materials and Methods: The study population consisted of thirteen consecutive female patients who had been previously irradiated for HD in our department. All patients had mediastinal disease with or without involvement of the cervical nodes. An experienced radiation oncologist defined the planning target volume corresponding to the ISRT technique on the CT scans of each patient. The lungs and breasts, which are characterized by a high susceptibility for radiation carcinogenesis, were manually delineated on a slice-by-slice basis. Three-dimensional plans were generated with 6 MV X-ray beams giving 30 Gy to the tumor site in 15 fractions. Differential dose-volume histograms (DVHs) of the breasts and lungs were calculated by the radiotherapy plans. The dose calculation interval was equal to 0.01 Gy in all histograms. The DVHs were used to determine the organ equivalent dose (OED) of the lungs and breasts and the relevant patient- and organ-specific lifetime attributable risk (LAR) for cancer development with the aid of a non-linear mechanistic model. The above risk model accounted for the effects of the tumor dose fractionation in radiotherapy and the repopulation ability of each tissue between two dose fractions. The estimated LARs were compared with the respective organ-dependent lifetime intrinsic risk (LIR) values of cancer induction for unexposed people as provided by the most recent SEER Cancer Statistics Review.
Results: The OED of lungs due to ISRT for HD varied from 1.7 to 2.8 Gy whereas the respective variation for breasts was 0.3-1.3 Gy. The LAR for lung cancer development in irradiated females was 1.4-2.8 % depending upon the organ exposure and the patient's age. The corresponding radiotherapy-induced lifetime risk range for the appearance of breast malignancies was 0.2-2.6 %. The individualized LARs for lung cancer induction after ISRT were 2.2-4.3 times low in comparison with the LIRs. The probabilities for the development of radiation-induced breast malignancies were more than 4.7 times smaller than the respective LIRs.
Conclusions: The LARs for lung and breast cancer induction following ISRT for supradiagramatic HD in female patients are lower than the nominal cancer incidence rates but they should not be considered as insignificant. The presented probabilities for second cancer development may be useful for the follow-up of the HL survivors.
| O-32: Comparison of Volumetric Modulated Arc Therapy and Helical Tomotherapy Plans for High Risk Prostate Cancers Using Dosimetric and Radiobiological Indices|| |
Sneha S. Nair, M. K. Ashitha, P. S. Renil Mon, C. O. Clinto, E. Sreedevi, Raghavendra Holla, Bhaskaran K. Pillai
Department of Medical Physics and Radiation Safety, Amrita Institute of Medical Science and Research Center, Kochi, Kerala, India. E-mail: [email protected]
Introduction: Very few studies have compared various techniques of IMRT (Intensity Modulated Radiation Therapy) based on radiobiological indices in high risk prostate cancer till date. In high risk prostate cancer, the target volume includes pelvic lymph nodes in addition to the prostate and seminal vesicles. This makes target volume irregular and complex. Also, a lot of normal tissues will come into contact with target volume. Simultaneous Integrated Boost approach is used in high risk prostate cancer in which a higher dose is delivered to prostate and seminal vesicles compared to pelvic lymph nodes. This will make the treatment planning process in high risk prostate cancer more challenging compared to low and intermediate risk prostate cancer. In this study, we compare plan quality based on dosimetric and radiobiological parameters of ten prostate cancer patients using VMAT (Volumetric Modulated Arc Therapy and HT (Helical Tomotherapy) techniques.
Objectives: Aim of this study is to verify the efficacy of newly installed HT (Helical Tomotherapy) in comparison with the existing VMAT (Volumetric Modulated Arc Therapy) technique.
Materials and Methods: Ten patients treated with VMAT by Simultaneous Integrated Boost (SIB) approach were selected from our database. For each patient, two clinical target volumes were defined. Planning Target Volume 70 Gy (PTV70Gy) included gross tumor and entire prostate with 8 mm margin on all sides except posteriorly where a 5 mm margin was given. Clinical Target Volume 50.40 Gy (CTV50.4Gy) includes pelvic lymph node stations. A PTV50.4Gy was created with 3-mm auto margin to CTV50.4 Gy. Organs At Risk (OAR) rectum, bladder and femoral heads were also contoured. Each patient's data were exported to TomoTherapy planning station and new plans were created and compared with the existing VMAT plan. VMAT plans were done using Monaco5.1 for Elekta synergy 6MV accelerator. Dosimetric indices such as Conformity Index (CI), Conformity Number (CN), Homogeneity Index (HI), Dose Volume Histogram (DVH) and Radiobiological indices, Equivalent uniform Dose (EUD), Tumour Control probability (TCP) and Normal Tissue Complication Probability (NTCP) were compared. Other treatment parameters like beam on time and Monitor Unit (MU) were also analysed. Statistical significance of the comparison was reported using paired Student's t-test.
Results and Discussion: Both HT and VMAT are able to produce clinically acceptable plans with adequate target coverage. Differences in the high dose region of PTV70Gy DVH infer that both plans are not in congruence in case of homogeneity of dose distribution and hotspot inside the target volume. The homogeneity indices quantified as 0.03 (0.01) for HT and 0.06 (0.01) for VMAT plan. D2% of HT was 70.63Gy (0.29) and that of VMAT was 72.36Gy (0.61) The CI and CN values of PTV70Gy shows that VMAT plans are more conformal than HT plans. In case of OAR sparing, VMAT is more efficient in high dose sparing while HT give more low dose sparing. Analysis of plan quality based on Radiobiological indices showed only a marginal difference and which are not statistically significant. Treatment delivery time was about 60% higher in HT, MU also increased tremendously.
| O-33: Efficacy of Short Spinal Arc Length in Volumetric Modulated Arc Therapy Based Craniospinal Irradiation|| |
Upendra K. Giri, Biplab Sarkar, Kanan Jassal, Anusheel Munshi, Sandeep Singh, Salih Osman, V. Karthik, Tharmar Ganesh, Bidhu K. Mohanti
Department of Radiation Oncology, Fortis Memorial Research Institute, Gurgaon, Haryana, India. E-mail: [email protected]
Introduction: Medulloblastoma and primitive neuroectodermal tumours (PNET) are common paediatric tumours treated by CSI along with the systemic chemotherapy or (and) hormone therapy and surgery. Radiotherapy techniques for CSI include simulator based 2D technique, CT based three dimensional conformal radiotherapy (3DCRT), intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). The advantage of VMAT technique is that it does not require any junction shift since it employs overlapped fluence pattern between brain-spine and spine-spine fields to take care of dose matching in the junctions.
Objective: Objective of the study was to establish the dosimetric superiority of short arc lengths over large arc lengths, for craniospinal irradiation (CSI), using volumetric modulated arc therapy (VMAT).
Materials and Methods: For a cohort of ten patients, two VMAT CSI plans were created for each patient, one using the conventional full 360° arc (VMAT_FA) for the spine and the other using 100° posterior arc (VMAT_PA) for 23.4 Gy and 35 Gy prescriptions. In both the plans 360° arc fields were employed for treating cranial volume. Non-tumour integral dose (NTID), which is the dose to body excluding planning target volume, was compared with VMAT_FA and VMAT_PA plans. In addition to these VMAT plans, a 3DCRT plan was also created for all these patients to compare the NTID and target volume related dose constraints.
Results: Mean V95% difference between the two VMAT plans did not exceed 1.3% for cranial and spinal targets for both prescription levels. Conformity index, averaged over both prescription doses, were similar for VMAT_FA and VMAT_PA plans at 0.84 ± 0.04 and 0.82 ± 0.05 respectively. V95%, V110% and conformity index did not exhibit a statistically significant difference between partial- and full-arc VMAT plans. However, the VMAT_PA plan exhibited a lower NTID compared to VMAT_FA plans (0.007≤ p <0.05) in the 1-5 Gy range. Partial arc plans yields a statistically insignificant dose reduction for delineated organs, compared to full arc plans, except heart. PTV coverage as well as spillage dose to body-PTV is shown in Figure 1 and Figure 2 respectively.
|Figure 1: Comparison of PTV coverage (V95%) hot spot (V110%) and mean OAR doses between VMAT spine full arc, spine partial arc and 3DCRT|
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|Figure 2: Spillage dose to Body-PTV (NTID: non-tumour integral dose) for 3DCRT, partial arc VMAT and full arc VMAT for prescription dose of 23.4 Gy in left panel and for 35Gy dose in right panel respectively|
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Discussion: VMAT radiation treatment techniques are gaining popularity due to their simplicity and faster treatment delivery. In our study, we observed that use of partial arcs could substantially reduce the dose to kidneys, lung, larynx and body, although dose reduction in organs like liver, thyroid, heart, and bowel were not significant. For left kidney, a dose reduction to the magnitude of 5.2 Gy and 3.2 Gy were observed for VMAT_PA plans against VMAT_FA plans for prescription doses of 23.4 and 35 Gy. Dose to larynx was reduced by 2 Gy in VMAT_PA plans when the prescription dose was 23.4 Gy. Similarly, for lungs, partial arc plans resulted in a dose reduction of 1-2 Gy for both prescription levels; however, they were not statistically different. The only statistically different OAR doses were observed for bilateral kidneys in 23.4 Gy dose level.
[Supplementary Table 1] presents OAR doses reported by different investigators in the past. It is apparent that the ranges of reported OAR doses are wide and inconsistent. Kidney (combined and individual) doses were reported to be in the range of 4.4-13.2 ± 12 Gy for 36 Gy prescriptions in different reports. In our study, for a prescription dose of 35 Gy, dose to kidney(s) were 3.2-3.4 Gy for VMAT_PA plans and 5.5-6.5 Gy for VMAT_FA, pointing to better plan quality observed for VMAT_PA plans.
| O-34: A Hybrid Conformal Planning Technique with Solitary Dynamic Portal for Post-Mastectomy Radiotherapy with Regional Nodes|| |
K. Mohamathu Rafic, Timothy Peace Balasingh, Ebenezer Suman Babu, I. Rabi Raja Singh
Department of Radiotherapy, Christian Medical College, Vellore, Tamil Nadu, India. E-mail: [email protected]
Introduction: Computing an optimum treatment plan for post-mastectomy radiotherapy (PMRT) with regional nodes (supraclavicular and axillary nodes) is one of the challenging tasks in radiotherapy. At present, field-in-field (FinF) technique is a widely accepted for breast radiotherapy. However, very few reports on PMRT with regional nodes have been reported in the literature. Further, there is no published data that deals with fluence verification of dynamic FinF portals.
Purpose: The primary objective of this study focuses on incorporation of a solitary dynamic portal (SDP) in conformal planning for PMRT with regional nodes with an intention to overcome the treatment planning limitations imposed by conventional techniques. Secondary objective is to demonstrate in-air fluence verification of SDPs using amorphous silicon electronic portal imaging device (EPID).
Materials and Methods: 24 patients who underwent surgical mastectomy followed by PMRT were included in this study. The planning CT images patients from the level of “C2” to “start of adrenals” were acquired using Biograph True Point HD CT (Siemens Medical Systems, Germany). Initially, a treatment plan comprising of tangential beams fitted to beam's-eye-view (BEV) of chest-wall and a direct anterior field fitted to BEV of nodal regions, both sharing a single isocenter was generated using Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA). FinFs (10 to 15 fields) were added only in the medial tangent that were re-fitted to BEV of entire target volume and shared about 30-50% beam weight of medial tangent thereby increasing the tumor dose across the nodal regions while reducing the dose above and below the direct anterior portal. These multiple lower weight (3-5% relative weight per field) irregular FinFs were then converted into a dynamic field referred to as “solitary dynamic portal”. Dosimetric analysis of treatment plans were performed and compared with summed doses of chest-wall and regional nodes treatment plans computed with typical tangential conformal beams with dynamic wedges and tilted direct anterior field respectively. Furthermore, fluence verification for the dynamic portals was performed using EPID and portal dosimetry software.
Results and Discussion: Conformal plans with SDP showed excellent dose coverage (V95% >95%, V105% <6.5% and V107% <0.5%), higher degree of dose conformity (≤1.25) and homogeneity (≤0.12) without compromising the OAR sparing for PMRT with nodal-region. Treatment plans with SDP considerably reduced the lower isodose spread to the ipsilateral lung, heart and healthy tissue without affecting the dose homogeneity. Since, majority of dose contributions are from static tangents, the dose to lung (ipsilateral and contralateral) and contralateral breast were comparable to the typical conformal plans. Furthermore, we have recorded considerable reduction in heart dose (V25 Gy ≤ 10.1 ± 1.4%). SDP fluence map generated in our study is less complex than IMRT portals, having lower MU in the order of 45 - 60. Furthermore, gamma evaluation showed more than 96% pixel pass-rate for standard 3%/3 mm dose-difference and distance-to-agreement criteria. Hybrid conformal plans with SDP offers less probability of “geometrical-miss” at the highly irregular chest-wall with regional nodal radiotherapy.
Conclusion: From our results we conclude that the hybrid conformal plans with SDP would facilitate improved dose distribution and reduced uncertainty in delivery and promises to be a suitable treatment option for complex post-mastectomy chest-wall with regional nodal irradiation. The future scope of this study is to adapt deep inspiration breath-hold technique while delivering the dynamic portal to avoid displacement of dose gradients and thereby enabling higher degree of dose homogeneity across the moving target.
| O-35: Simultaneous Integrated Boost for Carcinoma Left Sided Breast: Plan Quality Comparison of Helical Tomotherapy With Volumetric Modulated Arc Therapy|| |
B. Subbulakshmi, T. K. Bijina, A. Pichandi, C. A. Muthuselvi
Department of Radiotherapy, Healthcare Global Enterprises, Bengaluru, Karnataka, India. E-mail:[email protected]
Introduction: Breast cancer is the leading cancer diagnosis among women in developed countries, and it is one of the most common cause of cancer death globally. It is well known that breast conservation with lumpectomy and adjuvant radiation treatment has shown to improve both local control and overall survival in early stage breast cancer patients. Simultaneous Integrated Boost (SIB) in breast conserving radiotherapy is known for its advantage in reducing dose to normal tissues with relatively lesser skin toxicity and reduced number of fractions.
Objective: To quantify the dosimetric results of Helical Tomotherapy (HT) and Volumetric Modulated Arc Therapy (VMAT) plans using the SIB technique for carcinoma left breast.
Materials and Methods: Nine left sided female breast patients were selected for this retrospective study. The patients were immobilized using thermoplastic cast with the abduction of hands above head. CT scan images of slice thickness 2.5 mm were acquired on GE PET CT scanner in supine position as per the institution protocol. The acquired images were transferred to Eclipse Treatment Planning System (TPS) and Planning Target Volume (PTVBreast), PTVBoost volume and OAR's such as heart, contralateral breast, ipsilateral lung and contralateral lung were delineated by radiation oncologist. Both PTV's were cropped 5 mm from skin. The prescription dose was 60.2 Gy to boost volume and the entire breast volume received 50.4 Gy in 28 fractions. The VMAT plans were generated using two partial arcs in the Monaco5.1 TPS. Monte Carlo dose calculation algorithm was used to calculate VMAT plans. The HT plans were done in VoLO TPS and the plan parameters comprised of 2.5-cm field width, pitch value 0.287 and Modulation factor 2-3. Beam entry was restricted by directionally blocking from contralateral side. Collapsed cone convolution dose calculation algorithm was used to calculate HT plans. The optimization prescription was defined to deliver prescribed dose to 95% of the target volumes and to minimize the volume receiving ≥107% of the boost dose. The quality of plans were evaluated by calculating Homogeneity Index (HI), Conformity Index (CI),mean dose to OAR's such as ipsilateral and contralateral lung, heart, contralateral breast, volume dose to ipsilateral lung and heart.
Results and Discussion: The mean volume of PTVBoost and PTVBreast were 102.62 cm3 and 877.39 cm3 for nine patients respectively. The target coverage (D95) was similar for PTVBreast in both plans, whereas in VMAT plans, the PTVBoost received nearly one Gy more than the prescription dose. The mean and minimum dose to PTVBoost were 62.08 ± 0.47 Gy and 57.57 ± 0.69 Gy for HT plans and for VMAT plans it was 62.51 ± 0.29 Gy and 57.50 ± 0.86 Gy. Minimum dose to PTVBreast was 37.52 ± 3.26 Gy and 35.84 ± 2.96 Gy. The maximum dose to PTVBoost was lower by 2% in HT plans than VMAT plans The plan quality parameter D2% for PTVBoost was lesser in HT plans compared to VMAT plans (63.78 ± 0.61 Gy vs 64.34 ± 0.41 Gy).The conformity (1.15 vs 1.21) and homogeneity (1.06 vs 1.07) index were better in HT plans compared to VMAT plans. The average beam on time was 7.57 min and 1.9 min for HT and VMAT plans. The mean dose to the heart, ipsilateral lung, contralateral lung and breast were similar in both plans. HT plan resulted in lower volume for heart dose, measuring 10, 30 and 40 Gy compared with VMAT (6.5% vs. 7.1%, 0.35% vs. 1.07%, and 1.97 vs 3.48%, respectively). The low dose volume (V5) for heart in HT plan were 19.6% higher, whereas volume receiving 5 Gy for ipsilateral lung was 17% lesser in HT plans compared to VMAT plans.
Conclusion: HT plans produced plans of higher quality and conformal dose distributions, at the cost of longer planning and treatment times compared to VMAT plans.
| O-36: Biological and Dosimetric Evalution of Flattening Filter Free Beam Plans Over Flattened Beam Beam Plans in Head and Neck Cancer|| |
K. K. D. Ramesh, Vyankatesh Shejal1, Ch. Chandrasekhar Reddy, Rama Krishna
Department of Radiotherapy, Manipal Super Specialty Hospital, Vijayawada, Andhra Pradesh, 1Department of Radiotherapy, Manipal Hospital, Bangalaru, Karnataka. India. E-mail: [email protected]
Purpose: To quantitatively evaluate the Biological and Dosimetric differences in VMAT plans with Flattening Filter Free (FFF) and Flattened photon Beam (FB) in H and N cancers.
Materials and Methods: Treatment plans with volumetric modulated arc therapy were generated for 10 Head and Neck patients for both flattened and unflattened photon beams on Elekta Infinity linear accelerator with Agility MLC system using Philips Pinnacle® treatment planning system (V9.8). Beam energy of 6 MV was chosen for all cases and identical dose constraints, Arc angles and number of Arcs were used for both flattened and unflattened photon beams. The Gross Target volume (GTV) and planning target volume (PTVP) were contoured for the individual treatment plans. Total prescription was 60 Gy (54 Gy for PTVp and 60 Gy for GTV). In order to analyze the biological effectiveness of treatment plans, dose volume histograms (DVH) were utilized. Flattened and FFF beam plans are quantitatively compared.
Results: The FFF beam plans provided improved dose sparing compared to the flattened beam plans. Overall, the FFF beam provides lower mean and maximum dose and NTCP values to OARs.
Conclusions: In general, the treatment plans utilizing FFF beam can provide similar target coverage as that of flattened beam with improved dose sparing to OARs. Significant dose sparing effect is obtained for the cases involving relatively large field sizes due to lower dose to the out-of-field region compared to flattened beam.
| O-37: Use of Portal Dosimetry to Monitor Treatment Consistency for Head and Neck Cancer Throughout the Course of Treatment|| |
Sudesh Deshpande, Suresh Naidu, Vikram Mittal, R. Bajpai, V. Anand, V. Kannan
P.D. Hinduja National Hospital and MRC, Mumbai, Maharashtra, India. E-mail: [email protected]
Purpose: Use of portal dosimetry software to check treatment delivery consistency and to monitor changes in patient anatomy during course of treatment.
Materials and Methods: Varian portal dosimetry software and Electronic Portal Imaging Device (EPID) aS1200 were used to study consistency of treatment. Patients undergoing VMAT treatment for head and neck cancer were enrolled in this study. Patient plan was delivered after correcting set up error and transmitted images were acquired by the EPID aS1200 during the treatment. The transmitted dose images were acquired by EPID after the beam passes through patient. Images were acquired in continuous mode at source to imager distance SID = 150 cm on the 1, 2, 3, 5, 10, 15, 20, 25 fraction number. Before measuring transmitted dose images cone beam CT was performed to eliminate any set up error. Day one transmitted dose images were defined as base line images. On an average 8 images were acquired during treatment for each patient. These images were compared with base line image. Gamma index evaluation was performed with 1 mm and 1% parameter using Varian portal dosimetry software.
Result: For the first five images i.e. up to tenth fraction we got average gamma index passing 98.3% which is within action level threshold of 97%. We observed gamma passing percentage varies during fag end of treatment. For 18% of patient gamma passing variation was more than threshold level at fraction number 20.
Conclusion: Dosimetric measurement during treatment is good tool to investigate error during the treatment. Portal vision is mostly used for patient set up and pre treatment QA of patient. We found that portal dosimetry is useful tool for checking consistency of treatment delivery and monitoring changes in patient contours.
| O-38: Identification of Equivalent Lung Volume from 4DCT Data for Treatment Planning and Delivery in SBRT of Lung Cancer|| |
N. V. N. Madhusudhana Sresty, A. Mallikarjuna, T. Anil Kumar, A. Krishnam Raju
Basavatarakam Indo American Cancer Hospital and Research Institute, Hyderabad, Telangana, India. E-mail: [email protected]
Introduction and Objectives: Motion correlated CT (4DCT) is frequently used for lung cancer cases and it is a most important requirement in SBRT of lung. Usage of conventional CT for lung tumor leads to several types of artifacts due to different respiratory phases and limited field of view. Most of the studies clearly demonstrated that, the lung tumor motion is very complex and hysteric in nature. Hence, patient specific motion correlated CT is highly essential for hypo fractionated SBRT planning to identify the internal target volume. But, there is a considerable lung volume variation with different phases of 4DCT. Again, these volumes are different from the ungated CT lung volume. This is an important factor for the cases which are suitable for Gating. Hence, the objective of this study was to determine the suitable lung volume for treatment planning purpose from the 4DCT data.
Materials and Methods: 10 patients of stage I non small cell lung cancer (NSCLC) were analyzed in this study. All cases were treated by hypo fractionated SBRT. 3D and 4DCT scans were taken using brilliance big bore CT unit (Philips Medical Systems, The Netherlands). 4D CT scans were done using Real time position management system (Varian Medical systems, Palo Alto, USA) and 4D imaging software available with our CT. In this procedure, a marker block was placed on the patient's thorax. The markers were tracked by infrared camera. The respiratory signals were recorded based on these reflecting markers during breathing. Coached breathing helped us for better scans. The 4D data sets were sorted out for ten phase bins (0% to 90% phases). We evaluated maximum intensity projection (MIP), average intensity projections (Avg. IP) and minimum intensity projections (Min I P) with all generated phases using brilliance software. All the CT data sets were then transferred to Eclipse treatment planning system (Varian Medical systems, Palo Alto, USA). Lung volumes were identified in all the data sets.
Results and Discussions: We found that the CT data of average intensity projections (Avg I P) is closely matching with 3D CT data, with a maximum difference of 3.2% of the total lung volume. Also, 20% phase and 80% phases looked similar to average intensity projection volumes with maximum variations of 1.8% and 2.7% respectively. The lung volume in MW was clearly less in all the cases with the maximum difference of 9.1%. This is due to the fact that, the ITV in MIP is created with the union of GTVs of all the phases.
Conclusions: The lung volume derived from either Avg. IP or mid inhalation phase or mid exhalation phase should be used in the treatment planning for lung cancer. Though, MIP is useful in the identification of ITV, this phase underestimates the lung volume. This method can be utilized for non gating treatment. But, proper data set selection is very important in the treatment planning if the patient is identified for gating based treatment delivery.
| O-39: Novel Method of Error Reduction in Quantifying the Shift in Isocenter Using Line Spread Function Approach|| |
C. Vineeth, Manoj S. Kumar, C. V. Midhun, M. M. Musthafa
Centre for Radiation Physics, University of Calicut, Calicut University, Malappuram, Kerala, India. E-mail:[email protected]
Purpose: Application of Line Spread Function in minimising the experimental errors associated with the QA test for verifying the accuracy of position of radiation isocentre in Radiotherapy. Conventionally 2 mm is accepted as the tolerance in fixing the isocentre.
Materials and Methods: Two sets of EBT3 Gafchromic films were irradiated in the conventional angles, one under the gantry star pattern configuration and the other in arc mode exposure using a needle, of 1 mm dia, placed at the isocentre along the gantry axis as shown in Figure 1. The error estimation for first film is done using conventional metre scale measurement and digitalised image processing method. The second set of film is analysed using LSF method using image processing. LSF is generated by the line shadow of the steel needle created in the film, which is fixed on EPID positioned at 105. The process is performed both in stationary mode and single full arc mode under identical condtion. The arc mode exposure is expected to produce broadening in the LSF, if there is any shift in central axis.
|Figure 1: Schematic diagram of experimental setup and projections of needle in the stationary and arc mode exposures|
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In the first conventional setup, width of the center darkness is measured with common metre scale having least count 1 mm for an image of size 2 mm leading to an estimation of 50% error. In the second method the above pattern is subjected to digitilization using a digital scanner having 300 dpi under normal mode. The image was processed using ImageJTM software, based on the optical density profile of the region of interest. This results in a Gaussian distribution. This information is converted in ASCII format (8 bit) and reduced chi-square fit is performed. The pixels were converted into mm with 0.1 mm/pixel. The FWHM is evaluated as 1.6 mm with a relative error of 6.25% leading to an absolute error of 0.104 mm at the peak postion. This is significanly lesser in comparison with the error found in the conventional approach.
In the third method, the second set of films are exposed under arc mode and stationary mode, the films are scanned and processed using ImageJTM software and the crossline profile is generated for both cases and Gaussian fit is performed.The image is magnified to correspond 0.01 mm/ pixel. The FWHM of the LSF generated in stationary and arc mode are analysed as shown in Figure 2. The difference in width of LSF in each case is taken as the shift in isocentre. Present measurement gives a shift of 1.23 mm with an error of 0.141 mm and having percentage error of 7.1% leading to an absolute error of 0.01 mm.
|Figure 2: Gaussian fitted and measured line spread functions in the LSF based exposures|
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Result: The error assosiated with the conventional star pattern tests are verified and shows a very higher relative error of 50% with absolute error of 1 mm. When it modifies with the digital verification through the chi-square minimized gaussian fits, the error then reduces into 6.25% with absolute error of 0.1 mm. With an approach of Line Spread Function (LSF), the absolute error reduces to 0.01mm. This leads to absolute errors in each case to 1 mm, 0.1 mm and 0.01 mm respectively. Using this approach, we can define the new limits for QA programme which is meaningful in present situations like SRS that demands sub-mm precesion.
Conclusion: The random error associated with conventional star pattern test is evaluated with chi-square minimized Gaussion fit on the digitalized cross line profile of the film increase the accuracy by one order. The LSF approach improves the accuracy by further one order leading to higher order accuracy in advanced radiotherapy procedure.
| O-40: Developement Of a Cmos-Based Optical Computed Tomography System for 3D Radiotherapy Dosimetry|| |
Nurul Farah Rosli, Hafiz Mohd Zin, Ahmad Taufek Abdul Rahman1,2
Oncology and Radiological Sciences Cluster, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Penang, 1School of Physics and Material Studies, Faculty of Applied Sciences, 2Faculty of Applied Sciences, Universiti Teknologi MARA, Selangor, Malaysia. E-mail: [email protected]
Optical Computed Tomography (CT) is a bench top 3D imaging system for radiochromic PRESAGE dosimeters. The imaging system reconstructs dose distributions delivered to PRESAGE that changes its colour when irradiated. Alternatively, magnetic resonance imaging (MRI) may be used for imaging the dosimeter but MRI is not widely accessible. Current optical CT systems in the market are based on CCD image sensor and have slow imaging speed. The study characterises components in a CMOS-based optical CT imaging system developed in-house and investigates the feasibility of the system for imaging 3D radiochromic dosimeters. The study exploited recent advances in CMOS image sensor (CIS) technology to improve the imaging speed of the optical CT system. A rotary stage was constructed using a stepper motor to hold and rotate the dosimeter between the CIS and a large area LED. The components of the imaging system were integrated and controlled using LabVIEW (National Instrument, Austin, TX). A graphical user interface (GUI) was also developed to acquire projection images of the dosimeter. The measured field of view (FOV) of the CIS is 125 mm by 90 mm that can cover the whole PRESAGE dosimeter. A projection image can be captured at every 1.8 degree rotation of the dosimeter at every second that would amount to 200 projection images for a 360 degree rotation. Current limitation of the imaging speed is the rotation speed of the motor of 1.8 degree per second which can be improved with upgrading the stepper motor. At an imaging speed only limited by the maximum sensor frame rate of 28.5 fps, the scanning time will be reduced to 7 second compared to 200 second. A green dye solution of various concentration was used to mimic variation in PRESAGE colour from its response to radiation dose. The solution was filled in a plastic cylinder to study the linearity and uniformity of the system. The results show that the system is capable of capturing the projection images of a 3D translucent object with good linearity and uniformity. Further experiments will be carried out to optimise the development of the system to reconstruct dose distributions in 3D from a PRESAGE dosimeter.
| O-41: Measurement and Comparison of Surface Dose of Unflattened and Flattened Photon Beams for Different Field Sizes|| |
P. Suresh Babu, Sebeerali, Daicy George, V. Ramya, S. Sowmya Narayanan
Department of Radiation Physics, Vydehi Institute of Medical Science and Research Centre, Bengaluru, Karnataka, India. E-mail: [email protected]
Purpose: Flattening Filter Free (FFF) x-rays can provide more efficient use of photons and a significant increase of dose rate compared with conventional flattened x-rays, features that are especially beneficial for Stereotactic Radio Surgery (SRS) and Stereotactic Body Radiotherapy (SBRT). FFF x-rays are thought to offer dosimetric advantages such as reduced peripheral doses, out of field scatter doses and head scatter. The FFF beams contain more low energy components and have softer energy spectra than the corresponding flattened beams which can lead to increased dose in the build-up region. Meanwhile the FFF beams undergo less head scatter because the flattening filter is absent from gantry head of the linear accelerator, which may decrease the dose in the build-up region. Thus the two competing factors determine the build-up dosimetric characteristics of the FFF photon beams. The purpose of this study was to investigate the surface dose of FFF photons in the build up region and to compare it with that of conventional flattened photons.
Materials and Methods: Versa HD linear accelerator (Elekta Medical Systems, UK) has been in full clinical operation with 6MV, 10MV, 6FFF and 10FFF photons. Surface dose was measured using Markus parallel plate chamber (PTW Freiburg) with electrometer (PTW UNIDOSE) in solid water phantom. All four beams delivered for different field sizes ranging from 5 x 5 cm2 to 30 x 30 cm2. A solid water phantom (perspex slabs) was set up with SCD of 90 cm. The build-up depths for 6MV flattened and FFF beams were 0, 1, 2, 3, 4, 5, 16 mm and for 10MV flattened and 10 FFF beams were 0, 1, 2, 3, 4, 5 and 22 mm. We maintained 10 cm backscatter material. In this study surface dose is defined as the dose at a depth of 0.5 mm with respect to the dose at dmax.
Results: Surface dose increased linearly with field sizes for both FFF and flattened photons as shown in Figure 1. The FFF beams had marginally higher surface dose than flattened beams for smaller field sizes, but had lower surface doses for larger field sizes. The surface dose of 22.7% at 5 x 5 cm2, 28.94% at 10 x 10 cm2, 38.55% at 20 x 20 cm2, 46.39% at 30 x 30 cm2 for 6 MV flattened beam compare to 25.38% at 5 x 5 cm2, 30.29% at 10 x 10 cm2, 36.23% at 20 x 20 cm2, 39.64% at 30 x 30 cm2 for 6 FFF beams. Also, 16.58% at 5 x 5 cm2, 23.83% at 10 x 10 cm2, 35.56% at 20 x 20 cm2, 43.51% at 30 x 30 cm2 for 10 MV flattened beam and 21.15% at 5 x 5 cm2, 26.15% at 10 x 10 cm2, 31.86% at 20 x 20 cm2, 34.65% at 30 x 30 cm2 for 10 FFF beams as shown in Figure 2.
|Figure 1: Relative Surface Dose normalized to the 10 x 10cm2 reference field size|
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|Figure 2: Variation of Surface doses with field size for flattened and FFF beams for jaw settings of 5 x 5 cm2 to 30 x 30 cm2|
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Conclusion: The FFF photons have a higher surface dose than that of the corresponding flattened photons for field sizes smaller than 10 x 10 cm2 and lower surface dose for larger field sizes. It indicates that softer energy is more present in FFF beams whose contributions are proportionally more in smaller field sizes. For larger field sizes, in flattened beams the filter contribution itself is very larger results in higher scattered electrons. Though FFF tends to give higher surface dose as compared to FF beams for smaller field sizes, the overall surface dose values are well within the prescribed limit. Hence higher surface dose levels in FFF beams may not yield clinical significance.
| O-42: Determination of Stereotactic Small Field Output Factors with Different Detectors|| |
Seby George, Henry Finlay Godson, A. Sathish Kumar, Y. Retna John, B. Paul Ravindran
Department of Radiotherapy, Christian Medical College, Vellore, Tamil Nadu, India. E-mail: [email protected]
Introduction: Accurate dosimetry of small photon fields in modern radiotherapy is challenging due to lateral electronic disequilibrium, partial occlusion of source, steep dose gradients, and size of the sensitive volume of the detector as well as itscomposition. These challenging effects instigated an investigation on the acquisition of output factor with different type of detectors.
Objectives: To determine the output factor for small radiation fields defined by micro multi-leaf collimator and circular cones with different types of detectors and decide on the appropriate detector for small field dosimetry.
Materials and Methods: Small field output factor measurements were carried out using 6 MV photon beams in Primus linear accelerator with BrainLab mMLC and circular cones as add-ontertiary collimators. PTW microDiamond, PTW SRS diode and PTW pinpoint ion chamber were used toacquire output factors of square fields (0.6 x 0.6 cm2 to 10 x 10 cm2) and circular fields (1 cm to 4 cm diameter) defined by BrainLabmMLC and circular cones respectively. Output factors were measured with a source-to-surface distance of 100 cm at a depth of 10 cm in PTW MP3 RFA for all measurements.
Results: The data obtained with different detectors show differences in output factor for all collimating systems. Good agreement in output factors of BrainLab mMLC and circular cones were observed in field sizes greater than ~ 2 x 2 cm2 for all detectors and all tertiary collimators. The spread in output factors of different detectors with PTW microdiamond reference values for the stereotactic fields shaped by BrainLab circular cones is depicted in Figure 1. For the smallest cone (1 cm diameter), pinpoint ion chamber underestimate the output by 4.8% whereas SRS diode overestimate the output factor by 1.7% when compared to PTW microdiamond detector. The influence in output factors for small fields due to the presence of BrainLab mMLC as add-on accessory to the Primus linear accelerator is depicted in Figure 2. For the smallest field (6 x 6 mm2) defined by BrainLab mMLC, an underestimation of 23.9% and an overestimation of 1.9% were noticed with pinpoint ion chamber and SRS diode respectively.
|Figure 1: Comparison of output factors for the fields shaped by BrainLab circular cones with different detectors|
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|Figure 2: Comparison of output factors for the fields shaped by BrainLab mMLC with different detectors|
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Daisy chaining method has been adopted to correct the over response of SRS diode detector in the determination of output factors of circular fields and square fields. The output factors obtained with SRS diode were compared with the reference value (PTW microdiamond detector) and the percentage deviation has been reduced to 0.7% and 0.2% for 1.0 cm and 1.5 cm diameter cone respectively.
Discussion: The microDiamond detector has shown to be a promising detector for the measurements of output factors in small fields. The sensitive volume of the microDiamond detector is relatively large and exhibits volume averaging effect. But this effect is partially compensated by the over-response of the detector due to the presence of high density material. The volume averaging across the beam due to the relatively large sensitive volume is the main cause for the lower values measured with pinpoint ion chamber. The over-response noticed with diode detector in small fields is due to the presence of a high density silicon chip and the non-water equivalency of the dosimeter.
Conclusion: The output factor values were observed to be highly dependent on the configuration of secondary and tertiary collimator and the position of detector as well. Monte Carlo simulation with appropriate codes would improve the accurate determination of output factors while eliminating the experimental uncertainties.
| O-43: Quality Assurance Program at Durham Regional Cancer Center, Ontario Canada|| |
D. Patel1, M. D. Jensen1,2, D. Mason1
1Radiation Oncology Medical Physicist, R. S. McLaughlin Durham Regional Cancer Centre, Lakeridge Health, Oshawa, 2Department of Radiation Oncology, University of Toronto, Ontario Canada. E-mail: [email protected]
A comprehensive quality assurance (QA) program is an essential component of safe and effective radiation oncology practice. The objective of this presentation is to provide an overview of the QA program of the Durham Regional Cancer Centre (DRCC), a clinic that delivers approximately 2700 courses of radiation therapy per year in Ontario Canada.
The DRCC radiation oncology program is subject to regulatory requirements from the national nuclear energy regulator, and provincial health and labour authorities, who stipulate a set of safety requirements for the QA program to meet. However, the larger quality assurance program is based on guidance documents created by an alliance of the radiation treatment professional societies (physicians, physicists, therapists) in Canada, known as the Canadian Partnership for Quality Radiotherapy (CPQR). The Technical Quality Control Guidelines published by CPQR, available free of charge, provide the technical basis from which the quality control (QC) procedures for the radiotherapy equipment at DRCC are based. The technical QC results are monitored and reported to the local Radiation Treatment Quality Assurance Committee, as recommended by CPQR. The committee oversees all quality within the radiation program, including monitoring of quality indicators, incident reporting, and staff's maintenance of certification.
A set of software forms the core of the QA program documentation. Sharepoint manages the lifecycle of the policies, procedures and forms of the QA program, as well as the assignment and tracking of recurring (monthly or less frequently) QA tasks to physicists and physics associates. QATrack+ is a free, open source, QA database platform used to collect the results of QC procedures, including daily morning tests performed by the therapists. QATrack+ includes simple reporting and plotting, and is built on a modern database allowing for 3rd party reporting software if necessary. Email notifications are generated when QC tests fall outside of tolerance limits, alerting the physics team to potential issues. Finally, physicist activity (projects and machine QC) are logged in a weblog, powered by the free and open-source software package elog. This provides a central, searchable and widely accessible platform for documenting physics activities. Service engineer activity is currently logged in hard-copy log books, but online logging is being investigated. Results of technical QC performed on the equipment are reviewed weekly and monthly by a physicist. Each treatment unit is assigned to a primary physicist, who has responsibility for ensuring QC activities and resulting actions are completed. Annual QC testing is also the responsibility of the primary physicists. Independent review of the annual QC is completed by a different physicist in the group. External review and comparison occurs through several activities, such as output and IMRT planning tests with IROC, and planning and delivery comparisons against other centres in Ontario.
The quality assurance program at DRCC is constantly evolving to meet the requirements of the clinic and nation and provincial regulations and guidelines. For example, the program is shifting many tests to Doselab EPID-based collection, which eliminates the need for special devices and allows faster collection and analysis of VMAT-related QA measurements. Further refinements are continually being made based on the data analyzed from the software databases. Continuing improvement of the QA program is a vital part of providing safe and effective radiation treatment.
| O-44: Study on the Measurement of Surface and Buildup Doses Using Different Ionization Chambers|| |
E. Sreedevi, C. O. Clinto, P. S. Renilmon, S. Sneha, Raghavendra Holla, Bhaskaran K. Pillai
Department of Medical Physics and Radiation Safety, Amrita Institute of Medical Sciences, Kochi, Kerala, India. E-mail: [email protected]
Introduction: In the measurement of surface and buildup doses, active volume and the electric field inside the chamber play an important role. According to the difference in chamber design (parallel plate or cylindrical), arrangement of field lines inside the chamber varies. The role of volume becomes vital if the region of measurement is a steep gradient one. Any detector will average the dose over its volume. If the dose varies over the volume of the detector, this average effect can give a different signal compared to the signal obtained by a point detector. Both the above factors can cause considerable differences in their responses in a gradient region.
Objective: The goal of this work was to study the effect of different ion chambers on the measurement of surface and buildup region doses.
Materials and Methods : A 30 x 30 x 30 Water phantom with a fine micrometer alignment tool was positioned on the treatment couch of Elekta Synergy® Linear accelerator with field size 10 x 10 in SSD 100 cm. For analyzing the volume effect, cylindrical chambers 0.01 cm3 (SCANDITRONIX WELLHOFER CC01), 0.125 cm3 (TN31010, PTW-Freiburg) and 0.6 cm3 (TN30013, PTW-Freiburg) were used. The parallel plate chamber 0.4 cm3 (IBA PPC 40) was also used to compare the field gradient effect. Cylindrical chambers 0.6 cm3, 0.125 cm3 and 0.01 cm3 were centrally aligned with their effective point of measurement (0.6 rcavfor photons and 0.5 rcav for electrons as per recommendation). Phantom was exposed with 6MV, 4MV photons and 6MeV, 8MeV electrons. The same alignment can be done for the buildup region also. Meter readings were noted and the doses were calculated for both the positions by correcting for temperature, pressure, polarity and saturation. The above measurements were done with a parallel plate chamber of volume 0.4 cm3 (PPC 40) where the effective point at the front surface of the cavity. Most detectors will show a slight dose rate dependence. It should be considered before performing the measurement.
Results and Discussion: As the volume of the chamber increases, the dose averaging effect also increases. Larger volume underestimates the point dose in gradient regions like surface or buildup region. The gradient effect of electric field is more for cylindrical chamber because of its design. And these effects were observed much significant at the surface. As per the recommendation, for parallel plate chambers the effective point of measurement is at the inner face of the front plate and for cylindrical one, it is displaced 0.6 rcav for photons and 0.5 rcav for electrons from the center. Even with this recommended shift, observed a difference in doses at both surface and buildup region. With a guard electrode, parallel plate chambers are having a uniform field strength throughout the volume. In cylindrical geometry, electric field is not constant (E= -grad V). This can cause a difference in their responses.
| O-45: Impact on Gamma Index on Measurement with Two Different Array Detectors|| |
S. Praveenkumar, M. Muthukumaran, Mariyappan
1Department of Radiation Oncology, Apollo Speciality Hospital, Chennai, Tamil Nadu, India. E-mail: [email protected]
Objective: The Feasibility of estimating Patient – Specific Quality Assurance is the predominant solution for VMAT Quality Assurance. The main objective of the study is to analyze the Gamma Index prediction Accuracy for small field VMAT patients with two different Detectors.
Materials and Methods: Thirty patients of 6MV of FF Beam with Field Size of less than 10 × 10 cm2 who underwent VMAT in our Facility were retrospectively selected. VMAT plans were created using Eclipse Treatment Planning System and were transferred to a Varian True beam STx which has HD 120 MLC configuration. The Measurements have been taken with an Octavius 4D Phantom which motorized and cylindrical which has diameter of 320 mm and length 343 mm. The density of the phantom is 1.05 g/cm3.
The detector of Octavius 729 detector which has large field coverage and better detection of hot spots is selected and Octavius Detector 1000 SRS which has liquid filled ionization chambers with presized detector spacing is selected.
The measurements have been analyzed with the PTW Verisoft software. Hence, using all these we study the Impact of Gamma Index on both the Detectors. The Gamma Index pass Rates were evaluated under 3% 3 mm and 2% 2 mm criteria with a Threshold of 10%. 2D Gamma, 3D Gamma and 3D volume Gamma for both Local and Global is verified.
Results and Discussion: The Gamma Index pass rates in the planes of Coronal, Sagittal and Transversal is analyzed. We compare the results of both the detectors. As the result, the Gamma Index passing rates is higher due to the High Spatial Resolution and High Accurate Dose measurements of very small regular and irregular fields and regions with steep dose gradient in 1000 SRS is slightly greater than that of Octavius Detector 729. In SRS 1000 Detector the passing rates for both local Gamma and Global Gamma is very much higher in all planes.
Conclusion: Based on our study and Results obtained with two different detectors, we can infer that the Octavius 1000 SRS predicts the better Gamma passing percentage for the small field VMAT Patient- Specific Quality Assurance.
| O-46: Volumetric Modulated Arc Therapy Dosimetry QA Using Liquid Ionisation Chamber|| |
Nitin R. Kakade, Rajesh Kumar, S. D. Sharma, Sudesh Deshpande1, D. Datta
1Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, 2P.D. Hinduja Hospital and Medical Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction: Volumetric Modulated Arc Therapy (VMAT) is an advanced radiotherapy technique capable of producing complex dose distribution in single or dual arc rotation. It improves the conformity as well as delivers homogeneous dose to target volume. Because of the presence of steep dose gradient between target volume, organ at risks and normal structures as well as the contribution of manifold intensity modulated small fields approaching from different directions, it becomes essential to perform pre-treatment dose verification using a suitable detector. Pre-treatment dose verification of VMAT using liquid ion chamber can enhance the confidence for precise and accurate dose delivery from the complex techniques.
Objective: To explore practicability of a liquid ionization (LIC) chamber (PTW microLion) for dosimetry QA in an advanced radiotherapy techniques such as VMAT.
Materials and Methods: The PTW microLion liquid ionization chamber having sensitive volume of 0.0017 cm3, filled with isooctane liquid was used for this study. The stand-alone high voltage supply and calibrated UNIDOS webline electrometer was used for charge measurement. The LIC was polarized at 800 V. All the measurements were performed with Varian TrueBeam linear accelerator for 6 MV filtered photon beam. The dosimetric characteristics which include repeatability, sensitivity, dose response, monitor unit linearity, dose rate dependence and output factor were studied. The repeatability and sensitivity of 0.13 cc air ion chamber (AIC) was also studied and sensitivity of both detectors was compared. Dose rate dependence of LIC was studied with dose rates of 60, 100, 200, 300, 400, 500 and 600 MU/min. The LIC was cross calibrated against the 0.13 cc ion chamber in two different orientations: the LIC was positioned such that the beam was parallel to the detector axis (axial orientation) and perpendicular to the axis (perpendicular orientation) with the sensitive volume centred at 0.975 mm from the entrance window. The perpendicular orientation calibration factor was applied for pre-treatment dose verification. All the measurements were performed in 1D Scanner water phantom at 5 cm depth with a source to surface distance of 100 cm for field size of 10 x 10 cm2. For pre-treatment dose verification, a dedicated insert was fabricated to incorporate LIC at proper location in the IMRT thorax phantom. The insert was able to replace with insert which can incorporate 0.13 cc ionization chamber. This heterogeneous thorax phantom consists of different materials, representing tissues inside the thorax: lungs, spinal cord and soft tissue. The computed tomography scans of phantom were send to treatment planning system (TPS) and planned dose were recalculated. The five treatment plans of different sites were chosen for this purpose and absolute point dose measurement were performed using LIC and AIC respectively. The TPS calculated and measured dose were compared.
Result: The sensitivity of LIC and AIC in perpendicular orientation was found to be 10.14 and 3.47 nC/Gy respectively. The response of the LIC was 2.92 fold more than the AIC. The repeatability and output factor of LIC was found to be within 0.02% and 0.76% respectively. The percentage difference between the TPS calculated and measured dose ranges from -0.84 to +1.46 and -2.29 to +2.05 for LIC and AIC respectively.
Discussion: The liquid ionisation chamber results appear closer to TPS calculated dose in comparison to air ionisation chamber. It may be attributed to small sensitive volume of LIC. The study also confirms that the liquid filled ionization chamber may also be a suitable detector for pre-treatment dose verification of VMAT.
| O-47: dosimetric characteristics of digital megavolt imager for Flattening Filter Free beams|| |
S. Vendhan1,2, R. Murali2, N. Arunai Nambiraj3, M. Muthukumaran1, 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: New amorphous silicon based electronic portal imaging device (aS-EPID) called Digital Megavolt Imager (DMI) (aS1200) has higher pixel resolution (0.34 mm) and increased active area (40 x 40 cm2) than its predecessor aS1000 (0.39 mm and 40 x 30 cm2). The new aS1200 detector panel is also capable to acquire dosimetric (integrated over all frames) images of Flattening Filter Free (FFF) beams at higher dose rates.
Objective: To evaluate the dosimetric characteristics of aS1200 megavolt (MV) detector for flattening filter free (FFF) beams.
Materials and Methods: Recently commissioned Varian Truebeam SVC linear accelerator at our clinic is equipped with aS1200 MV detector panel. The dosimetric response of the detector for 6X-FFF beam was tested and evaluated for its signal saturation, linearity with dose, dose-rate dependence, change in Source-Detector Distance (SDD), signal lag (ghosting), and back scatter contribution from imager Exact-arm (E-arm).
To evaluate the linearity, detector was positioned at 100 cm SDD, irradiated with 6X-FFF beams at the maximum available dose rate (1400 MU/min) and dosimetric images were acquired for 3 different square fields (3 x 3 cm2, 10 x 10 cm2 and 40 x 40 cm2) irradiated with 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 250, 300, 400, 500, 750 and 1000 monitor units (MU). 100 MU were delivered at various dose-rates 400, 600, 800, 1000, 1200 and 1400 MU/min for field sizes 3 x 3 cm2, 10 x 10 cm2 and 40 x 40 cm2 and acquired images were analyzed for dose-rate dependency. Change in detector response with SDD were studied by acquiring images for 100 MU at various SDD ranging from 100 cm to 150 cm for 3 different field sizes (3 x 3 cm2, 10 x 10 cm2 cm to and 25 x 25 cm2) at 1400 MU/min dose-rate. The effect of signal lag was evaluated at both minimum (400 MU/min) and maximum (1400 MU/min) dose-rates by acquiring 3 images of 100 MU each: a 30 x 30 cm2 (reference image), next after five minutes with a 15 x 15 cm2, followed immediately by irradiating second 30 x 30 cm2 (ghost image) and measuring residual signal left in it. The MUs were increased to 250 and 500 for 15 x 15 cm2 field and the intensity of ghosting effect was studied. Dosimetric images were acquired for 100 MU at different field sizes >8 x 8 cm2 and the ratio of detector signals at ±3 cm from the center pixel along the Gun-Target direction was calculated to evaluate back scatter contributions from imager support arm. Recommended setting of 2 mm x 2 mm Region of Interest (ROI) was used throughout the study to sample the dose in the detector.
Results and Discussions: The detector signal to MU ratio drops drastically at lower MUs below 25 MU. For irradiations between 50 to 1000 MU, the signal to MU ratio varies within 0.7% and reaches maximum at 100 MU for all field sizes as shown in Figure 1. The detector linearity with dose is within 1% and no evidence of signal saturation as such. The aS1200 response variation across various dose rates and SDD for all field sizes is <0.4% and <0.2% respectively. The effect of ghosting increased distinctly at higher dose rate but however it is negligible (0.1%). The impact of back scatter at all field sizes is <0.3% because of additional shielding provided at the back of the detector.
Conclusion: Our initial study results on dosimetric characteristic of DMI detector at high dose rate FFF beams has shown its potential ability as a pretreatment verification tool for FFF beams.
| O-48: Study on Radiological Properties of Wooden Dust as a Substitute of Lung for the Dosimetric Purpose|| |
Priyusha Bagdare, Swati Dubey, Om Prakash Gurjar1
School of Studies in Physics, Vikram University, Ujjain, 1Roentgen-SAIMS Radiation Oncology Centre, Sri Aurobindo Institute of Medical Sciences, Indore, Madhya Pradesh, India. E-mail: [email protected]
Introduction: The thoracic cavity poses complexity in accurate dosimetry due to its curved topology and heterogeneity coupled with inner organ motions. The heterogeneity in thoracic region arises mainly due to the combination of chest wall, lung and soft tissue behind the lung. In order to quantify the dose delivered to a tissue of interest, the measurement is done on the phantom. As ~ 65% of human body consists of water, thus the phantoms suggested for dosimetry are homogenous and water equivalent whereas human body comprises of varied densities which make it complex heterogeneous medium.
To develop such a heterogeneous phantom there is a need of material which can mimic the heteroginties inside the thoracic cavity. Present study focuses on determination of radiological properties of wooden dust which can represent the lung part of thoracic cavity and can be use for designing thoracic phantom in future.
Objective: To study the radiological properties of wooden dust using 6 mega voltage (MV) photon energy.
Materials and Methods: Density of wooden dust of pine and thoracic region of patient were calculated by Hounsfield units (HU) measured from computed tomography (CT) images of each medium. The depths of isodose curves of 100%, 95%, 90%, 85%, 80%, 75%, 65%, 60%, 55% and 50% were measured in CT images of both the mediums on TPS for 10 × 10 field size.
Photon beam of 6 MV energy with field size 5 × 5, 7.5 × 7.5, 10 × 10, 12.5 × 12.5, 15 × 15 and 17.5 × 17.5 cm2 was incident on CT images of chest wall and on combination of slab wooden dust slab (SWS) perpendicular to the surface as shown in Figure 1. Dose at depth 4 cm and 10 cm with field size 5 × 5, 7.5 × 7.5, 10 × 10, 12.5 × 12.5, 15 × 15 and 17.5 × 17.5 cm2 were measured on CT images of patient and in the combination of SWS using anisotropic analytical algorithm (AAA) on treatment planning system (TPS). Same measurements were taken on linear accelerator (LA) for the SWS combination with the help of ionization chamber.
|Figure 1: Isodose curves in CT slice of actual patient and in combination of slab-wooden dust-slab|
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Results and Discussions: The mean density of wooden dust, slabs, soft tissue, chest wall and lung was found to be 0.271, 0.994, 0.980, 0.947 and 0.287 gm/cc respectively. The isodose depth (of 100%, 95%, 90%, 85%, 80%, 75%, 65%, 60%, 55% and 50%) for patient (1.53, 2.97, 4.23, 5.57, 7.39, 9.52, 11.28, 12.82, 14.42, 15.95 and 17.66 cm) and for SWS (1.47, 2.92, 4.14, 5.43, 7.05, 9.03, 11.19, 13.75, 16.83, 20.15 and 23.85 cm) are approximately same. The mean percentage variation between planned dose on CT images and combination of SWS at depth 4 cm and 10 cm for field size 5 × 5, 7.5 × 7.5, 10 × 10, 12.5 × 12.5, 15 × 15 and 17.5 × 17.5 cm2 were found to be -0.3079 and -0.4599 respectively. The mean percentage variation between planned and measured dose for combination of SWS at depth 4 cm and 10 cm for field size 5 × 5, 7.5 × 7.5, 10 × 10, 12.5 × 12.5, 15 × 15 and 17.5 × 17.5 cm2 were found to be -0.0453 and 0.0236 respectively.
Conclusion: The radiological properties of wooden dust are found to be equivalent to that of lung, thus it can be use as a lung substitute for designing chest phantom in future.
| O-49: Evaluation of Setup Uncertainties and Clinical Target Volume to Planning Target Volume Margin for Various Tumor Sites with VMAT Treatments Using CBCT|| |
Dilip Kumar Ray, Srimanta Pramanik1, Poonam Ray2, Arko Choudhury1, S. K. Asik Iqbal1, Amithabh Roy1, Sayan Kundu1, Sandip Sarkar1
Department of Medical Physics, Chittaranjan National Cancer Institute, 1Department of Medical Physics, Ruby General Hospital Ltd., 2BC-185, Sudha Apt. Samarpally, Krishnapur, Kolkata, West Bengal, India. E-mail: [email protected]
Objective: The aim of this study was to determine the patient setup errors for different tumor sites based on clinical data for the treatment of volumetric arc therapy (VMAT) using pre-treatment verification with KV-CBCT and also we found out the institutional based CTV to PTV margin for various sites based on an analysis of systematic and random errors.
Materials and Methods: In this study the tumor sites were divided in three categories 1) Head and Neck (37 number of patients), 2) Thorax (18 number of patients) and 3) prostate (17 number of patients). All the patients underwent pretreatment verification by KV-CBCT imaging for the determination of overall distributions of setup corrections in the directions of anteroposterior (Z), mediolateral (X) and craniocaudal (Y) with 3D vector length and also CTV to PTV margins were analyzed from ICRU 62, Stroom's and Van Herk's formulas.
Results and Discussions: The displacements were within ±3 mm in 14.28% case in anteroposterior direction (AP), in 15.58% case in mediolateral direction (ML), and in 11.03% cases in craniocaudal direction (CC) for H and N tumor. For thorax lesion the displacements within ±3 mm in 16.32% case in (AP) direction, in 17.14% case in (ML) direction, and in 18.77% cases in (CC) direction. The displacements were within ±3 mm in 14.07% case in (AP) direction, in 21.97% case in (ML) direction, and in 15.06% cases in (CC) direction for prostate tumor as presented in Figure 1. The cumulative frequencies of 3D vector length of ≥5 mm were rare for Head and Neck (H and N) but more common for thorax and prostate case at 9.79% and 12.83% respectively. The largest magnitude of systematic error for H and N, thorax and prostate lesions were 0.129 cm in vertical (Z) direction, 0.148 cm in longitudinal (Y) direction and 0.144 cm in lateral (X) direction respectively. The largest magnitude of random error for H and N, thorax and prostate lesions were 0.167 cm in lateral (X) direction, 0.290 cm in longitudinal (Y) direction and 0.303 cm in longitudinal (Y) direction respectively. The CTV to PTV margins for H and N calculated by ICRU formula were 2.34 mm, 2.32 mm and 2.39 mm; by stroom's formula they were 3.50 mm, 3.51 mm and 3.68 cm; by van Herk's formula they were 4.1 mm, 4.10 mm and 4.33 mm (X, Y, Z directions). The CTV to PTV margins for thorax calculated by ICRU formula were 2.44 mm, 3.51 mm and 2.81 mm; by stroom's formula they were 3.43 mm, 4.98 mm and 3.93 cm; by van Herk's formula they were 3.93 mm, 5.72 mm and 4.50 mm (X, Y, Z directions). The CTV to PTV margins for prostate calculated by ICRU formula were 3.33 mm, 3.49 mm and 2.76 mm; by stroom's formula they were 4.76 mm, 4.86 mm and 3.91 cm; by van Herk's formula they were 4.76 mm, 4.86 mm and 3.91 mm (X, Y, Z directions).
|Figure 1: systematic error for H and N, thorax and prostate lesions in vertical (Z) direction, longitudinal (Y) direction and lateral (X) direction. (1) H and N, (2) Thorax, (3) Prostate|
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Conclusion: For the better target coverage and dose distribution, van Herk calculated CTV to PTV margin is adequate for most of the tumor site except SRS and SRT for brain tumor. The establishment of institutional based PTV margins and reducing of setup uncertainties frequently CBCT is essential because setup errors vary according to each immobilization systems, patients and daily setup.
| O-50: Radiotherapy with Tele-Cobalt Machine: Efficacy and Need for Tissue Compensation in Head and Neck Treatments|| |
Cachar Cancer Hospital and Research Centre, Silchar, Assam, India. E-mail: [email protected]
External Beam Radiotherapy (EBRT) remains the mainstay for radical treatments, in malignancies in head and neck regions. Head and Neck malignancies form around 50% of radiotherapy patients in the north eastern parts of the Indian subcontinent. Because of less inter-field separations, the penetration requirements of the treatment plans makes the telecobalt beam sufficient for executing radiotherapy, with proper immobilization and use of wedges if required. Inter-field thickness variations and irregular contour affect uniformity in delivered doses, and adverse reactions are encountered because of skewed isodose curves seriously affecting the volume dose variations in treatment planning. Normal tissue reactions, affect effectiveness of the treatment and therefore deter the Quality Of Life (QOL).
EBRT with a telecobalt machine (Theratron 780C) started in 2006 and completed a decade at our centre. About 15 patients per day receive radiotherapy for head and neck treatments. To overcome skin reactions and excess dose due to small contour of neck, a need was felt to introduce tissue compensation. Ellis type tissue compensation using 1 cm thick Aluminum metal is introduced. The tissue deficiency is measured by an L shaped gridded type Lucite frame work. For individual patients the custom type compensator tray is prepared on a Lucite plate, mountable in the shadow tray of the cobalt machine. The attenuation coefficient of metal rods μ=0.1462 cm-1 (1cm Al = 2.57 cm water). A simple type of POP immobilization is prepared in place of thermoplastic immobilization shell. The Lucite mounting tray has attenuation about 4%.
Lateral opposing fields with compensation reduced resultant isodoses 180% and 170% in neck and chin levels to 150% with uniform tumor volume homogeneous dose of 160%. Portal radiographs with and without compensator showed uniform tissue irradiation, also a method to verify field positions. This method is applied to all the head and neck radiotherapy patients receiving lateral field treatments. So far about 40 patients completed full course of radical radiotherapy with least skin morbidity, and overdose effects significantly brought down. This makes telecobalt treatments more effective, good patients compliance and this plan could be feasible in all centres. In the era of high technology radio-therapy, these type of innovations at hospital level promotes cost-effective radical treatments to cancer patients, because cancer care all over the globe becomes unaffordable.
| O-51: Evaluation of CBCT and 4DCT Based Planning Target Volumes in Non-Small Cell Lung Carcinoma and its Effect On Critical Structure Doses|| |
K. Sebeerali, Vyankatesh Shejal, N. Vinod Kumar, R. Ramu, B. M. Vadiraja
Department of Radiotherapy, Manipal Hospital, Bengaluru, Karnataka, India. E-mail: [email protected]
Introduction: Large tumor motion often leads to larger treatment volumes, especially for the lung tumor located in lower lobe and adhered to chest wall or diaphragm. Variety of geometrical uncertainties such as respiratory motion, baseline variation and set-up errors, limits the precision of radiation therapy (RT) for lung cancer. According to ICRU report 62, internal target margin (ITV) and set-up margin (SM) should be included in the PTV to compensate geometrical uncertainties including tumor centroid movement, tumor boundary and set-up displacement. However, the tumor boundary displacement merely discussed about margin calculation previously. It would be assessed in present study.
Objective: Present study would evaluate changes in tumour motion magnitude and set-up error by 4DCT at planning and CBCT at treatment, and calculate the variation in planning target volume (PTV) margins devised from both imaging techniques to compensate for these changes.
Materials and Methods: Ten patients with the lung tumour located in lower lobe and adhered to chest wall or diaphragm that underwent VMAT were considered for the current study. Four-dimensional computed tomography scans (4DCT) were acquired at simulation to evaluate the tumor intra-fractional centroid and boundary changes, and Cone-beam Computed Tomography (CBCT) were acquired during each treatment to evaluate the tumor inter-fractional set-up displacement. Brilliance CT Big bore from Philips medical system along with Pinnacle 3 treatment planning system and XVI imaging from Elekta was utilized for current study. The margin to compensate for tumor variations uncertainties was calculated by using Van Herk et al margin calculation recipe published in the exiting literatures and PTV volumes were evaluated for its accuracy.
Results and Discussion: Current Study revealed that CBCT based margins overestimated the planning target volume in comparison with 4DCT based treatment planning volumes. This inaccuracy could be due to the fact that theoretical formula for margin calculation would fall inadequate as it does not incorporate the tumour motion seen in various respiratory phases of 4DCT scan. Hence it is recommended for the patients receiving external radiation for NSCLC; an ITV based approach shall be adopted for the estimation of PTV margins for accurate patient dosimetry.
| O-52: Design and Development of Miniature Primary Standard for Air-KERMA Measurement of Low Energy Synchrotron Radiation|| |
Sudhir Kumar, S. D. Sharma, D. Datta
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction: The limitation of the clinical imaging methods arise mostly due to insufficient spatial resolution, contrast and quantitative scaling. The advent of synchrotron radiation (SR) has the potential to override these limitations because of very high intensity beam and broad energy spectra. Further, monoenergetic photons extracted from synchrotron radiation offer the unique opportunity to study the energy response of radiation detectors. The SR source is available from INDUS-II high energy accelerator at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. The SR beam is generated at the bending magnet of the 2.5 GeV electron storage ring of INDUS-II accelerator. The SRs are essentially high intensity and predominantly low energy (critical energy 6 keV) photon beams used for various scientific studies. A dedicated beamline [Beamline-4 (BL-4)] has been provided at INDUS-II offering facilities for both the conventional as well as advanced x-ray imaging experiments. However, outputs of these beams (8 to 25 keV) have not yet been standardised due to non-availability of a suitable radiological standard.
For low energy region, the photoelectric effect is a dominant interaction process and the photoelectric cross section has a strong dependence on the atomic number of material. Hence, radiation detectors generally show strong energy response dependent characteristic in the low energy region. For the low and medium energy x-ray beams, the free-air ionization chamber (FAIC) is considered to be a primary standard for the determination of air kerma. The FAIC is an energy independent instrument as it relies on the principle that the walls of the chamber do not influence the measurement of charge. To fulfill this requirement, it was decided to design and develop a miniature FAIC to measure the air kerma rate from the low energy SR beams. This paper describes the constructional details as well as output measurement methods of SR beams using the locally designed parallel-plate type FAIC.
Materials and Methods: Ionization chamber: The miniature parallel-plate FAIC was designed and fabricated for SR beam up to 25 keV energy. The continuous slowing-down range, R csda for 25 keV is ≈1. 20 cm in air. The gap between the high voltage electrode and the collecting electrode to achieve the charge particle equilibrium (CPE) should be 2.4 cm. However, inter-electrode spacing was taken as 3 cm to avoid the loss of charged particles (i.e. electrons) created by interaction of synchrotron radiation in the defined collecting air volume. The seven guard rings made of copper of thickness 2 mm, electrically isolated from each other, were inserted at a regular interval of 2 mm in order to align and produce the uniform electric field over the interaction volume. These rings were connected in series to a chain of resistors (100 kilo-ohm each). Additionally, an enclosure with adequate shielding thickness (1 mm SS + 5 mm Pb + 1 mm SS) was provided around the chamber to keep the contribution of scattered and transmitted radiation as minimum as possible (within 0.01% of primary radiation). The salient features of the miniature FAIC is given in [Table 1] below. Output measurement of synchrotron radiation: The output of various monochromatic SR beams of BL-4 at Indus-II, RRCAT was carried out using this FAIC. For this purpose, the miniature FAIC was aligned perpendicular to the central beam axis of the SR beam for the field size mentioned in [Table 2] and was located at 30-meter distance from the tangent point of storage ring. The parallelism of the entry and exit apertures of the chamber with the SR beam line was verified using Gafchromic EBT3 film. In order to verify the inter-electrode spacing, the charge saturation at 25 keV was investigated experimentally. The charge (q ) was measured as a function of applied voltage (V ). The inverse of q was plotted against 1/V 2 and extrapolated to 1/V 2equal to zero from which the value of saturation charge (qs ) was derived. The charge collection efficiency (f ) at 25 keV for a derived value of saturated charge (6.543 × 10-9C) corresponding to 1800 V was estimated theoretically by using Mie's formula.
|Table 2: The measured air kerma rate of various monochromatic synchrotron radiation beams using locally designed miniature free air ionization chamber at 30 meter from the tangent point of 2.5 GeV electron storage ring|
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The chamber was irradiated by 8, 10, 15, 20 and 25 keV energies of SR beams. The average meter readings (charge) corresponding to each setting was corrected for variations in environmental conditions and other corrections factors mentioned later. The ion recombination correction was computed for each beam using two voltage method used for pulsed beam. The air kerma rate was determined using:
where q is the measured charge collected for one minute; ρair = 1.205 kg/m3, density of dry air (20°C and 1013.2 mbar); V air is the detector sensitive air volume; (w̄/e)=33.97 J/C; g is the average fraction of the initial electron energy lost by bremsstrahlung production in air and Πk i are the product of correction factors (recombination factor, k s, air attenuation factor, k a, polarization factor, k pol, photon scattered factor, k sc, electron loss factor, k e and transmission factor via front face/diaphragm, k t).
Results: At an operating voltage of 1800 V for the SR beam of 25 keV energy, the f (which is defined as the ratio of q by q s) was found equal to be 0.9989 at 1.36 Gy/min. The f estimated using Mie's formula was found equal to 0.9991. These two values of f are in excellent agreement to each other within 0.02% which indicates that additional margin of 0.6 cm in addition to 2.4 cm to keep the plate separation equal to 3 cm is sufficient to prevent any ion loss from the sensitive volume of the chamber. The air kerma measured using miniature FAIC at BL-4 at RRCAT, Indore for SR beam energies of 8, 10, 15, 20 and 25 keV is listed in [Table 2].
It is observed from the [Table 2] that the output of the beam is maximum at 15 keV which is expected as per the shape of SR spectra. The expanded uncertainty in the measurement of air kerma rate is 1.2% (k = 2).
Conclusions: The performance of this chamber was found satisfactory as per design and expectation and qualify to be a primary standard for measurement of air kerma rate of low energy synchrotron radiation beams of energy up to 25 keV. This chamber can be used for various dosimetry measurements with synchrotron radiation including calibration of another dosimeters.
Acknowledgement: T he authors express their sincere thanks to Shri P. K. Sahani, IOAPDD, RRCAT; Dr. G. Haridas, HPD, BARC; Shri Amit Jain, RSSD, BARC and Dr. Ashish Kumar Agarwal, TPD, BARC for their help in this work.
Suortti P, Thomlinson W. Medical applications of synchrotron radiation. Phys Med Biol 2003;48:R1-35.
Attix FH. Introduction to Radiological Physics and Radiation Dosimetry. New York: Wiley; 1986.
| O-53: Characterisation and Performance Study of Newly Developed N-TYPE Skin Diode Dosimeter for High Photon Energy (6 AND 18 MV) Skin Dosimetry|| |
Zakiya S. Al-Rahbi1,2, Dean L. Cutajar1,3, Ziyad A. Alrowaili1, Anna Ralston1,3, Peter Metcalfe1, Anatoly B. Rosenfeld1
1Centre for Medical Radiation Physics, University of Wollongong, Wollongong, 3St George Cancer Care Centre, St George Hospital, New South Wales, Australia, 2Department of Radiotherapy, National Oncology Center, The Royal Hospital, Muscat, Oman. E-mail: [email protected]
Purpose: To investigate the feasibility of using the newly developed n- type Skin Diode for in-vivo skin dosimetry through characterisation on the surface of a phantom simulating the condition for in-vivo skin dosimetry for megavoltage photon beams.
Materials and Methods: The response of the Skin Diode was investigated for different field sizes and radiation incident angles using both 6MV and 18MV photon beams. The percentage depth dose (PDD), dose rate dependence, dose linearity, output factor (OF), and exit doses were measured. All Skin Diode measurements were compared with the MOSkin TM and Attix ionisation chamber measurements.
Results: The Skin Diode showed a good linearity (R2 = 0.9928) for a dose range of 50 cGy to 500 cGy for both the 6MV and 18MV photon beams. For field size dependence, the Skin Diode measurements were within experimental agreement with the MOSkin TM dosimeter (3.66% for 6MV) and Attix chamber (3.93% and 3.38% for both 6MV and 18 MV photon beams respectively). For the 6MV photon fields (10 cm x 10 cm), the mean surface dose measurement of the MOSkinTM, Attix and Skin Diode were 18.3 ± 1.7%, 16.2 ± 0.1% and 25.5 ± 2.0%, respectively, with all measurements relative to the Dmax of each individual detector. The average PDD difference, beyond Dmax, between the MOSkin TM and Attix chamber was 1.9%, and between the Skin Diode and Attix chamber was 2.3%, for 10 cm x 10 cm 6 MV photon fields.
There was no significant dose rate dependence observed for the Skin Diode for 6 and 18 MV photon fields (within experimental error). The agreement in the exit dose measurements between the Skin Diode and Attix chamber was within ±2.4%.
Conclusions: In-vivo dosimetry is important during radiotherapy to ensure the accuracy of the dose delivered to the treatment volume. A dosimeter should be characterised based on its application before it is used for in-vivo dosimetry. The newly developed n-type Skin Diode responses were investigated on the phantom surface to determine its applicability to be used for in-vivo skin dosimetry. The Silicon Diode showed a feasible response to different field sizes, radiation incident angles, PDD, output, entrance and exit dose measurements. The entrance doses, as measured by the Skin Diode, were higher than desired, which will be corrected through a re-engineering of the top encapsulating layer through subsequent updates of the design. The Skin Diode may provide a good possibility for real time in-vivo skin dosimetry during external beam X-ray radiotherapy.
| O-54: NANO KCl:Sm3+ as a New Optically Stimulated Luminescent Phosphor|| |
Pratik Kumar, Mini Agarwal, K. Asokan1
Medical Physics Unit, IRCH, AIIMS, 1Inter-University Accelerator Centre, New Delhi, India. E-mail: [email protected]
Radiation is widely used in various applications like medical, industry, agriculture, research and military purposes. All these applications have their unique features and requirements. Some of them require small doses of radiations (μGys) like medical imaging and specific use of radiopharmaceuticals. Efforts are always made to reduce these doses further by inventing better technique and technologies. On the other hand a few applications such as industrial, food and military related need very high doses (in kGys) and some of them may be trying to escalate even further to test the forward limit. Obviously all such radiation applications entail hazard and warrant precise measurement of doses. Passive dosimeters like Thermo-luminescent Dosimeter (TLD) and relatively recent addition Optically Stimulated Luminescent (OSL) dosimeter are widely used for these purposes. However, there is only two commercial OSL phosphors namely Al2O3:C and BeO. The former form M/S Landauer is well known while the later is yet to be marketed aggressively. OSL has many advantages over TL as the former is excited by light which is controlled better unlike the later which is excited by heat. OSL is known to be able to measure smaller doses, has better reproducibility, has less cumbersome procedures, may be made portable and may measure the dose repeatedly for the same exposure. We attempted to prepare a new OSL phosphor KCl:Sm3+ (nano-crystalline) which may measure high radiation doses. Sm-doped nanocrystalline KCl was synthesised by solid state reaction at a high temperature of 200°C for 3 hours with high-quality precursors of KCl (M/S Merck, AR grade, 99.95 % pure) and SmCl2.6H2O (M/S Alfa Aesar, 99.5% pure). The sample was prepared by adopting the following reaction (chemical):
KCl + 2SmCl3.6H2O Heating at 363 K for 3 hours KCl: Sm + 6HCl + 9H2O
During synthesis, precursor KCl was mixed with various concentrations of dopant precursor Sm (such as 0.15mol%, 0.25mol%, 0.45mol% and 0.50 mol%) to investigate the role of concentration of the dopant Sm in OSL signal. The resultant product was grounded to prepare homogenous powder and was further subjected to thermal treatment at 80°-90°C for 3 hours to obtain fine nano phosphor. This nano powder was annealed (thermally) in Muffle furnace at various temperatures for 2 hours (from 650°-740°C) with a heating rate of 15°C per minute. In-situ cooling of the mixture up to temperature 300°C was achieved by keeping it in the furnace for about 20 minutes after switching the furnace off. The powder was taken out from the furnace when the temperature of the furnace falls to 300°C and was kept on the metal block at the room temperature for further cooling. The powder and pellet form of the same mixture was used for various studies. KCl:Sm3+ was made with varied concentration of Sm and the optimised concentration was found to be with 0.45% of Sm which gave the maximum OSL signal. We confirmed the structural and morphological characteristics of our phosphor with XRD which revealed its poly-crystalline nature with grain size 20-60 nm. This observation was also supported by the Selected Area Diffraction (SAD) pattern of Transmission Electron Microscopy (TEM). The presence of Sm in the KCl matrix was confined by Energy-Dispersive X-ray Spectroscopy (EDS) analysis while existence of trivalent Sm3+ was corroborated by X-ray Photoelectron Spectroscopy (XPS) analysis. The OSL response was linear from 100 mGy to 750 Gy. Our KCl:Sm3+ showed fading of 20% in 50 days and 7-8% in 12 days. It showed variation of 6-7% in signal for exposure-reading-annealing cycles. The overall sensitivity of KCl:Sm3+ was found to be about 80% of that of Al2O3:C and BeO. During course of preparation we did attempt to prepare KCl:Sm and KCl: Sm2+ as well but they showed much higher fading making them impractical for dosimetry. KCl:Sm3+ was found with least fading and highest sensitivity since trivalent Sm3+ created permanent and stable defects in the KCl lattice. Al2O3:C and BeO phosphor being propriety items are costly and therefore, indigenous search for other efficient OSL phosphor is the need of the hour. KCl:Sm3+ nano phosphor is an efficient doismetric material due to its storing efficiency and reusability which is highly desirable in radiation therapy and imaging in medical diagnostics. Because of its long linear dose response KCl:Sm nanophosphor is the efficient candidate for the space, military, food irradiation and other dosimetric applications and even futuristic real-time online dosimetery.
| O-55: Development of Cryostat Integrated TL/OSL Reader for its Application in Radiation Dosimetry|| |
Anuj Soni, D. R. Mishra, P. Kadam, D. Datta
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India. E-mail: [email protected]
Introduction: Thermoluminescence (TL) studies provide vital clues in connection with the mechanism of trap formation, concentration and nature of the traps. For a radiation phosphor generally, dose readout is carried out at the temperatures that are much higher than normal room temperature where shallow traps are ineffective and as such cannot contribute to the TL response. In OSL based dosimetry, however, the measurement is usually carried out at room temperature, where these shallow traps can significantly affect the OSL response. The TL measurement at low temperatures gives the useful information about such shallow traps which may be having metastable life-time of the order of a few ms at room temperature. It has been observed that these traps exercise a decisive influence over the OSL response of samples as they lead to a delayed optically stimulated luminescence (DOSL) in which charges released from dosimetric traps, upon optical stimulation get re-trapped at shallow traps. At lower temperatures (below room temperature), these traps may contribute to the total OSL signal and at the same time the contribution of higher temp TL traps will decrease due to the temperature dependence of photoionization cross-section. Thus, they can seriously affect the overall calibration factor for any dosimeter with the change in the readout temperature. This can have implication in optical fibre based online OSL dosimetry which can find application in medical dosimetry. This lead us to develop the low temperature TL/OSL reader to study the TL/OSL of Al2O3:C OSL phosphor to be used in optical fibre based OSL dosimetry.
Objective: Design and development of a programmable cryostat integrated TL/OSL reader to study the temperature dependence of OSL. These studies will give useful information on the effect of readout temperature on OSL signal and thus the overall calibration particularly in optical fibre based online OSL dosimetry having application in medical dosimetry.
Materials and Methods: A K-type thermocouple based PID circuit was used to control the temperature in the reader system. The reader comprises of a bialkali Photomultiplier tube as a detector having response in the range 300-700 nm, for detecting the luminescence. The reader is connected to the PC through an RS-232 serial interface. The commercially available α-Al2O3:C (TLD-500K) crystal from Laundauer Inc., was subjected to irradiation by UV light on the heater planchet held at various low temperatures. The sample was subjected to OSL measurement at various low temperatures.
Results and Discussion: A programmable cryostat integrated TL/OSL reader has been designed and developed to study the effect of readout temperature on the OSL intensity. The reader system measures the temperature of the planchet with ±0.5 °C precision. We report the results of OSL experiments on α-Al2O3:C, and of generalized numerical simulations of potential OSL behaviour with temperature. The photoionization cross-section of shallow as well as dosimetric traps has been evaluated numerically as well as experimentally. At lower temperatures, the photoionization cross-section of main dosimetric traps becomes very low (~10-20 cm2 at 250K) and they act like deeper traps and very less OSL is observed from them. The main TL glow peak due to this dosimetric trap is not found to be completely bleachable with blue light stimulation at low temperatures. Further, the TL peak (8oC at 0.33K/s) due to shallow trap becomes active at low temperatures and contributes in OSL more than the main dosimetric trap. It is concluded that the stimulation and irradiation/calibration temperatures need to be maintained fixed throughout the experiment i.e. the dose estimation process.
| O-56: Energy Dependence of Nanodot OSL Dosimeters to Low Energy X-Rays Using Monte Carlo Simulation Code EGS5|| |
V. L. E. Cruz1, S. Goto2, T. Okazaki1, H. Hayashi2, E. Tomita2, Y. Mihara2, T. Asahara2, T. Hashizume1,3, W. H. Cheng1, I. Kobayashi1
1Nagase Landauer, Ltd., Tsukuba, 2Tokushima University, Tokushima, 3SOKENDAI, Hayama, Japan. E-mail: [email protected]
Low energy X-rays have been increasingly used in medical diagnostic procedures. Procedures such as Computed Tomography, Interventional radiology, etc. uses low energy X-rays and results in the exposure of patient and in some cases, of the medical staff. Managing and measuring the radiation dose received by patients and medical staff should be done and a suitable radiation dosimeter must be used. A small type optically stimulated luminescence (OSL) dosimeter called “nanoDot” was designed and is expected to be used in measuring and estimating the radiation dose received from medical procedures using X-rays. nanoDots uses OSL technology which offers advantages over other types of passive dosimeters such as its ability to be read repeatedly since it uses visible light instead of heat to read the stored dose. However, in low energy X-rays, the response of the OSL dosimeter to incident photons is not constant and varies depending on the energy used for each situation. This is a concern when using nanoDots in radiation dosimetry for low energy X-rays. The main objective of this study is to evaluate the energy dependence of the OSL dosimeter to low energy X-rays, in particular; ISO narrow beam series X-rays, mono energetic X-rays and polychromatic X-rays used in medical diagnosis. This study also aims to evaluate the response of the nanoDot OSL dosimeter using different X-rays radiation qualities. The Monte Carlo simulation code EGS5 was used and experiments were carried out to determine the energy dependence of the nanoDot OSL dosimeter to ISO narrow beam series X-rays, polychromatic X-rays and mono energetic X-rays. The results from simulations and experiments were compared and the accuracy of the EGS5 simulation was evaluated. The experiments using ISO narrow beam series X-rays were carried out in the National Institute of Advanced Industrial Science and Technology (AIST) which is a primary standard in Japan. Furthermore, the experiments using polychromatic X-rays were also performed. The experimental data of ISO narrow beam X-rays were in good agreement with its simulation, and they were also consistent with the simulated data for mono-energetic X-rays. In addition, experimental data of polychromatic X-rays is also in good agreement with its corresponding simulation. These facts indicate that the use of EGS5 is a reliable way in determining the energy dependence of an OSL dosimeter. The energy dependence curve for polychromatic X-rays calculated by EGS5 simulation is different from the ISO narrow beam X-rays and mono-energetic X-rays, nevertheless the energy dependence curve of mono-energetic X-rays and ISO narrow beam series X-rays are the same. One reason of this difference is that the energy spectrum used in polychromatic X-rays is different with the ISO narrow beam series X-rays or mono energetic X-rays. This result shows that the energy dependence curve of the nanoDot also depends on the overall energy spectrum of the radiation source. Proper evaluation of the energy dependence is necessary for low energy X-rays since there are differences in the response depending on the energy spectrum of the radiation source. In Conclusion, Evaluation of the energy dependence of the nanoDot OSL dosimeter for different X-ray qualities is essential. This will allow the nanoDot to be a very reliable and suitable dosimeter in any situation for radiation dosimetry of patients and medical staff.
| O-57: Synthesis and Characterization Of Ho3+ Doped Hafnium Oxide TLD for Radiation Dosimeter|| |
Nandakumar Sekar, Bharanidharan Ganesan, Hajee Reyaz Ali Sahib, Prakasarao Aruna, P. Thamilkumar1, R. R. Rai1, Singaravelu Ganesan
Department of Medical physics, Anna University, 1Department of Radiotherapy, Dr. Rai Memorial Medical Cancer Centre, Chennai, Tamil Nadu, India. E-mail: [email protected]
Introduction: Cancer is a dreaded disease which is treated by Radiotherapy, Chemotherapy and Surgery. Radiotherapy plays a vital role in treatment of cancer and recently measurements of invivo radiation dosimeteric in patient is of great interest due to high dose gradients in advanced technology like IMRT, IGRT etc. Hence, for the last few decades, a great degree of interest has been shown for the hafnium oxide for radiation dosimeteric applications, due to its high dielectric constant, wide band gap and better interface properties such as chemical stability, conduction band offset and thermodynamic stability. In the present study, Synthesis and characterization of H03+ doped Hafnium oxide were carried out and its applications towards radiation dosimeter were investigated.
Materials and Methods: Pure and Extrinsic HfO2 NPs with different Ho content (2.5-10% in weight) was prepared by precipitation method and they were investigated by X-ray diffraction, FESEM-EDAX, UV-Visible Spectrophotometer, Fluorescence spectrophotometer, FTIR, Raman Spectroscopy, True Beam-Varian, Long stand and TLD glow curve determined by using Thermoluminescence Reader (Nucleonix TL 1009I).
Results and Discussion: Intrinsic and Ho3+ doped HfO2 powder were obtained by the precipitation route and calcined at 800°C for 2 hrs in air. The crystal structures, size of the resultant materials were investigated by powder X-ray diffraction (XRD) measurements. The obtained XRD-spectrum is in good match with the standard JPCDS. The composition and morphology of the synthesized NPs have been examined using FESEM-EDAX. The optical absorption spectra of Pure and Ho3+ doped HfO2 dispersed in water were recorded using a UV–Vis spectrophotometer. The band gap of the NPs was calculated from the UV absorbance spectra. The emission properties for various Holmium concentrations have been studied by means of Photoluminescence. The presence of the water related bonds in the samples were confirmed by using FTIR. Raman measurements show that the crystalline phase of monoclinic to cubic phase transformation and Evidence to the XRD. A typical TL glow curve of pure and dopant HfO2 pellets exposed to 10 MV X-ray photon beam were taken in order to in order to study the dose response of HfO2 for its application in Radiation Dosimetry and also its Reproducibility and Fading characteristic were carried out to study the trap parameters, including geometric factor (μg), activation energy (E) and frequency factor (s) associated with HfO2:Ho.
Conclusion: Pure and Ho3+ doped HfO2 NPs powder were synthesized and characterized to determine the Kinetic parameters and dosimetric characteristics. These favorable TL characteristics of prepared NPs may contribute towards the development of HfO2: Ho radiation dosimeters which can be effectively used for in vivo dosimeter in future.
| O-58: Patient Specific QA on Cyberknife M6 Robotic Radiosurgery System Using In-House Fiducial Based Polystyrene Phantom|| |
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: Placing the Phantom and measurement chamber as per the 'Align Centre' chosen during the treatment planning is very challenging for Cyberknife Radiosurgery Plans involving small fields. This step plays a major role in the patient specific QA as targeting multiple beams to the chamber is based on the align center. Hence the purpose is to design a polystyrene phantom for patient specific QA on Cyberknife M6 system which uses fixed tracking method.
Methods: Three pieces of polystyrene blocks of the dimensions 20 cm x 20 cm x 5 cm thickness are used for designing the phantom. A chamber holder for 0.01CC pinpoint chamber (IBA, Germany) is drilled to this block such that the chamber center is at 2.5 cm depth. Four numbers of stainless steel fiducials of 0.7 mm diameter are implanted to this block. Two more 5 cm polystyrene phantom blocks are implanted with one fiducial each making the total number of fiducials to 6. The chamber holder is sandwiched between these two blocks making the total thickness of the phantom to 15 cm. 4 aligning corner screws will hold the phantom blocks together without sliding. The position of all the fiducials are such that they do not overlap in 45 and 315 degree X ray images. All fiducials are fixed in the drilled position by pouring hot wax. CT Scan of the phantom is acquired and imported to Multiplan (ACCURAY, USA). A clinical treatment plan is overlaid on this phantom and the dose is calculated. This plan is delivered to the phantom on the treatment unit using fiducial tracking method.
Results: The phantom with the chamber is accurately placed using fiducial based tracking method. The measured dose in the phantom is in agreement to the planned dose within 3%.
Conclusion: A polystyrene fiducial phantom has been designed for patient specific QA on Cyberknife M6 system.
| O-59: Nanodots, Alanine, and Tld100H Dosimeters Investigations and its Treatment for Stereotactic Ablative Radiotherapy Pre-Treatment Verification|| |
N. U. Esen1,2, R. Prabhakar1,2, M. Geso2
1Peter MacCallum Cancer Centre, 2Medical Radiations Science, RMIT University, Melbourne, Victoria, Australia. E-mail: [email protected]
Purpose: Stereotactic Ablative Radiotherapy (SABR) is a standout amongst the chosen radiation therapy practices for early stage bronchogenic carcinomas. Procedures stretched to other treatment locales like Spine, Scapula and Sternum, and so on. Pre-treatment verification confirms the patient got the planning dose. Distinctive class of dosimeters or dose-measuring devices have been employed for pre-treatment check that incorporates ionization chamber, diode, TLD, 2D Array etc. SABR employed small fields which order the utilization of scale down detectors for pre-treatment confirmation. Alanine and nanoDots are new class of dosimeters that should be typified for pre-treatment verification. It was the aim of the present study to investigate the influence quality (e.g. energy, dose rate, directional dependency, etc.) of alanine, nanoDots dosimeters and compare with TLD100H and explore the feasibility of using these dosimeters for pre-treatment verification of the dose delivered to patients undertaking stereotactic ablative radiotherapy.
Methods: Bruker EleXsys E500 EPR spectrometer of 9.5 MHz was used to read the Alanine pellet dosimeters signals and the Harshaw QS 5500 automatic TLD reader was used for reading the TLDs. Also, Microstar Reader from Landauer Inc. was used to study the signal of the irradiated nanoDots OSL dosimeters. All the irradiation was done on ClinaxTH 21ix at 6MV x-ray beam. Three Dimensional (3-D) phantoms were design for each detector and were place separately inside in-house Rod phantom made of Perspex to perform SABR pre- treatment patient verification.
Results: The relationship between dose measured using Alanine, TLD100H and nanoDots dosimeters followed a linear curve (R2 = 0.998, R2 = 0.999, R2 = 0.989) and no meaning distinction with dose rate, and energy was observed for the detectors. The contrasts between the measured and the TPS computed dose were fewer than 2% and 3% with Alanine, nanoDots and TLD respectively. Specifically, the rate increment of nanoDots and alanine dosimeters to TLD is half.
Conclusion: From the results obtained, this study indicates that the SH EPR-Alanine pellets and nanoDots dosimeters are predictable and agree well between the measured and the figuring measurement. It likewise affirmed that both alanine and nanoDots dosimeters are profitable dosimeters for SABR pre-treatment verification.
| O-60: Investigating Polarity and Ion Recombination Effects of Six Ionization Chambers for Small Radiation Beam Apertures|| |
K. J. Maria Das, Arpita Agarwal1, Nikhil Rastogi1, S. A. Yoganathan, D. Udayakumar, Shaleen Kumar
Department of Medical Physics, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, 1Department of Physics, School of Science, IFTM University, Moradabad, Uttar Pradesh, India. E-mail: [email protected]
Objectives: Micro ionization chambers are the favorable dosimeter for small field measurements. However, because of their reduced sensitive volume, they are more susceptible to chamber specific effects such as polarity, ion recombination and leakage effects. The purpose of this study was to evaluate the polarity and ion recombination effects of small volume ionization chambers.
Materials and Methods: The polarity and recombination effect of six commercially available ionization chambers (Exradin A16 (0.007 cc), Exradin A18 (0.125 cc), IBA CC01 (0.01 cc), IBA CC13 (0.13 cc), PTW markus (0.055 cc) and IBA PPC 40 (0.40 cc)) were investigated for two photon beam energies; 6 MV and 15 MV. Each chamber was placed (perpendicular to the central beam axis) at a depth of 10 cm inside a radiation field analyzer (RFA, BP2, IBA dosimetry, Schwarzenbruck, Germany) and source to surface distance (SSD) was set to 100 cm. All the ionization chambers were connected to an electrometer (Unidos E, PTW, Germany) via a cable to collect the charge. The voltage was set to +300 V for all the ionization chambers and the meter readings were taken for the jaw collimated field sizes 0.5 x 0.5, 0.8 x 0.8, 1.0 x 1.0, 2.0 x 2.0, 3.0 x 3.0, 5.0 x 5.0 and 10.0 x 10.0 cm2 at dose rate 400 MU/min. The polarity of the applied voltage was reversed and same procedure was repeated to account the effect of polarity. In order to measure the ion recombination effect, the applied voltage was reduced to +100 V and again all the measurements were performed. The polarity correction factor (Kpol) and ion-recombination correction factor were calculated as per TRS 398 protocol. Same experiment was repeated for other depths i.e. dmax and 5 cm.
Results: Polarity effect was observed to be more at smaller field sizes i.e. <2 x 2 cm2; whereas for larger field sizes (>2 x 2 cm2) the Kpol was within the specified range (0.996 – 1.004). A16 ion chamber was the exceptional one which maintained Kpol value within the specified range even for small field sizes. The polarity effect was observed to be depending slightly on the measurement depth and it was higher at shallower depths compared to deeper depths. At dmax, the maximum deviation in Kpol values of ion chambers was in the order of ±3%; whereas the same was reduced to nearly ±2% and ±1% at 5 cm and 10 cm depths respectively. When comparing the polarity effect between 6 MV and 15 MV photon beam energies, it was found to be slightly larger for 6 MV. On contrary, the recombination correction factor was observed to be less than 0.5% for all measurements.
Conclusions: All the investigated chambers showed anomalous polarity effect at smaller field apertures except A16; whereas the recombination effect was found to be negligible (<0.5%) for all. The polarity effect was relatively larger for smaller field sizes below 2.0 x 2.0 cm2; it was highest for plane parallel chambers followed by A18 and CC13 ion chambers, while it was least for CC01 and A16 chambers.
| O-61: Small Field Dosimetry Measurements|| |
1Ex-Senior Radiation Scientist, ARPANSA, Australia, 2Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India. E-mail: [email protected]
Introduction: Modern radiotherapy treatment modalities such as Intensity Modulated Radiotherapy (IMRT), Volumetric Arc Therapy (VMAT) and Streotactic Radio Surgery (SRS) make use of small fields. Improper dosimetry in small field has led to few incidents harming the patients. There is no primary standard for absolute dosimetry. IAEA has proposed an ad hoc formalism to extend the reference dosimetry measurements done using IAEA TRS-398 and AAPM TG-51 protocols which implies the use of adequate correction factors. AAPM TG-155 and IAEA TRS-483 protocols for bringing uniformity in small field measurements are yet to be implemented. Experimental measurements done at ARPANSA by the author to issue advice on appropriateness of certain detectors for small field measurements and any other issues of small field measurements are presented in this talk.
Objectives: (1) Select the best detector for small field measurements for fields down to 5 mm diameter conical fields. (2) Determine the best geometry and reproducibility in measurements. (3) Achieve concurrence in output factors among the detectors. (4) Evaluate the correct sensitive volumes of solid state detectors which will improve the agreement between experimental and Monte Carlo calculated correction factors.
Materials and Methods: Beam profile measurements and output factor measurements were done using IBA blue phantom and Omnipro software. Measurements were done at 6 MV photon beam from Elekta Synergy accelerator. Field sizes used were MLC fields from 10 x 10 cm2 to 1 x 1 cm2 and Elekta SRS cones with diameters from 50 mm to 5 mm. The detectors studied were PTW 60017 electron diode, PTW 60019 micro-diamond, PTW Pinpoint chamber 31014 and IBA CC13 compact ionization chamber. Output factor measurements were done using PTW Unidos electrometer and the integrated charges for 100 MU were measured. A number of five readings were taken each time and standard deviation and estimated standard deviation of the mean were calculated. All measurements were done at 100 cm SSD, 10 cm depth in water. From the measurements of in-line and cross-line profiles the 80% - 20% penumbra widths and FWHM values were calculated using MATLAB script. For the evaluation of the sensitive volumes of solid-state detectors measurements were done at 100 cm SSD, 10 cm depth in water and square field of 10 cm x 10 cm with NE 2571 Farmer chamber calibrated against the primary standard graphite calorimeter and the solid-state detectors in the same geometry. The centering of the detectors were done by recording the profiles and tweaking the position of the detector so that the center of the profile lies on the central axis.
Results and Discussion: Reproducibility of profile scans with repeated MLC settings was <1% (0.8% for 1 x 1 cm2). Reproducibility of profile scans with SRS cones was <1% for cones of diameters 7.5 mm to 50 mm. Reproducibility with 5 mm cone was 1.25%. The output factors for the solid state detectors corrected using published correction factors lie within 1%. Uncertainty in measurements is estimated to be ~1.6% at 1 sigma level. The sensitive volumes for soild-state detectors along with the manufacturer's values are given. These values will reduce the disagreement between the experimental and Monte Carlo calculated values.
| O-62: Planning Considerations for Unflat Beams|| |
S. Sowmya Narayanan, P. Suresh Babu, V. Ramya, Daicy George, S. Geeta Narayanan1
Departments of Radiation Physics and 1Radiation Oncology, Vydehi Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, India. E-mail: [email protected]
Introduction: The advent of advanced beam therapy techniques, such as Stereotactic Radio Surgery/Radio Therapy (SRS/SRT) where inhomogeneous dose distributions are applied using intensity modulated radiotherapy (IMRT) or Volumetric Modulated Arc Therapy (VMAT) in which varying fluence pattern across the field are delivered have stimulated the increasing interest in operating standard Linear Accelerator (LINAC) in a Flattening Filter Free (FFF) mode. FFF beams show the potential for a higher dose rate and lower peripheral dose. Definite clinical benefits can be anticipated in the motion management using FFF beams since the beam ON time is less compared to FF. A National Task Group on acceptance criteria for flattening filter-free photon beam published by Atomic Energy Regulatory Board (AERB) was reviewed for this study.
Materials and Methods: A medical linear accelerator (Versa HD, Elekta Medical Systems, UK) having FFF photon beams have been installed in our centre recently. Commissioning of this LINAC was performed using standard protocols as prescribed by AERB. Baseline value for routine QA was established from Treatment Planning System (TPS) commissioned data. Parameters such as penumbra, degree of unflatness, surface dose were given prime significance for periodic performance evaluation of FFF beams. Treatment planning for dose delivery in this Linear Accelerator was carried out using TPS (Monaco v 5.11.01, Elekta Medical Systems) having various sophisticated algorithms. Planning was carried out for various treatment sites in Brain, Head and Neck, Thorax, Abdomen and Pelvis for different treatment techniques comparing FF and FFF beams. The planning considerations, dose fractionation regimes and dose constraints for Stereotactic techniques using FFF beams were also reviewed.
Results and Discussions: Dosimetric evaluation reveal that Plan quality of FFF beams used in 3D-CRT was inferior than beams. For IMRT and VMAT, plan qualities were comparable. FFF beams require more MU to deliver a particular dose as compared to FF beams, which does not pose any dosimetric disadvantage, owing to higher dose rate mode in FFF beams. Surface doses of FFF were comparable to FF beams. Planning considerations for Stereotactic techniques involves hypofractionated dose regimes with < 80% marginal dose coverage for PTV. Dose constraints need to be selected for the chosen dose fractionation regime. Report by Emami on Tolerance of Normal Tissue to Therapeutic Radiation was chosen in our institution. Planning aspects related to Monaco treatment planning system includes a minimal conformality constraint, whereas strict Normal Tissue Objectives (NTO) are used to achieve conformal distribution in Eclipse treatment planning system (Eclipse v 11.1, Varian Medical Systems, Palo, Alto). Motion errors for stereotactic techniques were corrected using 6D couch available with linear accelerator. Studies related to treatment planning and dose delivery of various clinical cases using FFF beams in modulated treatments demonstrate their clinical suitability and superiority over FF photon beams.
| O-63: Evaluation of System Accuracy and PTV Margins for SBRT in Lung and Liver Using Novalis TxTM Adaptive Gating and Exactrac® 6D System|| |
Himank Kalra, Anil K. Bansal, R. K. Munjal, Kartikeshwar Patro, H. Malhotra Singh, Naveen Kumawat
Department of Radiation Oncology, Max Super Speciality Hospital, New Delhi, India. E-mail: [email protected]
Target volume is of main concern for irradiation of tumors affected by the respiratory motion such as in lung and liver. With reduction of the target volume decreased complication rates of organs at risk is expected. Stereotactic body radiation therapy (SBRT) is popular choice with ultrahigh doses per fraction (6 to 30 Gy), in a hypo fractionated regimen of five or fewer fractions. To deliver such high doses per fraction respiratory motion need to be account during the course of radiotherapy. We used Novalis TxTM ExacTrac® Adaptive Gating technique for increasing accuracy in dose delivery and to reduce the target volume. System consists of a linear accelerator, two stereoscopic X-ray tubes, Infrared markers, camera and a 6D couch. The study was done using a phantom (ExacTrac® Gating Phantom) which contains a Dose Cube with dedicated slot for film placement below it and vertical moving platform with passive infrared markers to simulate patient's breathing pattern and is software controlled. Phantom is embedded with a 5 mm diameter steel ball and a 2 cm long helical marker similar to the gold marker used to insert into the patient's body using CT guidance. To Evaluate system errors Gated Winston lutz test was performed in gating condition with collimator opening of 10 mm by targeting the steel ball embedded in the Dose Cube with a EBT3 film just below the phantom. With the use of ExacTrac® Gating phantom Beam profile of 3 X 3 cm2 field size using EBT3 Gafchromic film by irradiating it with different beam on window (10%, 20%) under gating and non gating conditions are obtained. The cube phantom with a volume of 125 cc and equivalent sphere radius 6.2 cm is manually contoured using EclipseTM contouring station for 10 times on 10 different scan to find the volume of the contour and equivalent sphere radius to calculate contouring system error. For setup errors the intrafraction shifts of total 7 patients has been analyzed out of which 4 patients were of liver and 3 were of lung cases. Intrafraction shifts were applied 107 times during the treatment of these patients.
Result and Discussion: The Gated Winston lutz test showed a special accuracy of 1 mm. Beam penumbra increased by 1-2 mm as we go from no gating and gating with 10% beam on window to 20% beam on window. Average deviation in contouring volume in terms of equivalent radii was less than 1 mm. Maximum deviation between IR marker and KV-Xray setup are 1.44 ± 1.33 lateral, 4.78 ± 3.51 mm Longitudinal and 2.29 ± 0.91 mm Vertical with a standard deviation of 2.04 mm. Calculated PTV margin with account of beam penumbra shows 5 mm PTV margin is adequate for SBRT using ExacTrac® Adaptive Gating. Target volume with ITV+PTV and with PTV margins were analyzed for the same set of patients with average volume reduction of 50.8% ranges from 37-58%.
[TAG:2]O-64: Experience in Implementing and Conducting the Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM) Radiation Oncology Medical Physics Training Education and Assessment Program (ROMP-TEAP) in a Regional Australian Radiotherapy Centre[/TAG:2]
A. K. Mishra, D. Banjade, G. B. Warr, S. Tan, G. Dillon, G. Stevens, K. Thuraisingam, R. Hammond, M. Fuller, S. McDonell
Department of Radiation Oncology, Central West Cancer Care Centre, Orange Hospital, New South Wales, Australia. E-mail: [email protected]
Introduction: The shortage of clinically qualified medical physics specialist (QMPS) has been an acute problem in regional radiotherapy (RT) centres in Australia. The ACPSEM ROMP-TEAP has ameliorated this to some extent however it is still a challenge for some remote centres. Orange Health Service provides radiation oncology to the Far and Central West NSW region. The centre has experienced challenges in recruiting and retaining qualified Medical Physicists since it was established in 2010. However, despite this being an ongoing issue, a core team of QMPS has been established, which has enabled implementation of ACPSEM ROMP-TEAP at the centre.
Objectives: The objective of implementing this program at the centre is to address this workforce issue.
Materials and Methods: The centre used the methodology outlined in the ACPSEM Clinical Training Guide (CTG) for ROMP-TEAP. The program is supported by radiation oncologist, radiation therapist and professionals of radiology department. Brachytherapy training was performed at other specialised training centres.
Results: The centre has been running the program since February 2015 and has progressed from provisional to full accreditation as a training centre over a period of two years. A ROMP registrar was recruited to the program in 2015. The registrar has successfully achieved all the level two clinical learning outcomes of the program's CTG and passed the written exam component of the program. The registrar is on course to complete the clinical component of the program within the recommended 3-year timeframe and thereby complete all components of the program.
Discussion: Registrar has gone from being a trainee under close supervision to contributing to the clinical workload of the department under minimum supervision. Enabled review of department practices and implementation of kV therapy using AAPM TG 61 protocol. He has taken a leading role in the implementation of VMAT techniques in the department. The registrar also automated the light field vs X-ray QA checks with Matlab code.
Being a regional centre, there are less options to familiarise with more advanced RT techniques such as stereotactic radiosurgery, adaptive RT and Tomo therapy, however, core competencies were achieved by organizing visits to other centre as required.
Acknowledgements: Adrian Bailey and all staff of the CWCCC. The TEAP program is supported by the Commonwealth Government of Australia.
| O-65: Estimation of Eye Lens Exposure from Workloads During Interventional Procedures in South Africa, Taking Modifying Factors Into Account|| |
M. A. Sweetlove, A. Rose1, W. I. D. Rae2
Medical Physicist, Bloemfontein, South Africa, Departments of 1Community Health and 2Medical Physics, University of the Free State, Bloemfontein, South Africa. E-mail: [email protected]
Introduction: Eye lenses are radio sensitive organs, and cateractogenesis is the consequence of high levels of ionising radiation exposure. Use of Personal Protective Equipment (PPE) during interventional procedures significantly decreases the exposure to the eyes. In order to relate eye effects to exposure levels, some categorisation of dose levels is required. Operator dose estimation is a challenge if not measured directly, because of the many factors affecting dose and especially scattered dose. An estimate of the amount of exposure and how it is modified by eye PPE utilisation may be useful in scaling risk and grouping interventionists into eye exposure level categories. The objective of this study was to estimate the relative eye lens exposure from workloads of Interventionalists in the South African (SA) context taking modifying factors into account.
Materials and Methods: Workload was calculated from self-administered questionnaires completed by interventionalists (total 95) who indicated type of procedure, the number of procedures per week and the number of years worked with fluoroscopy guided interventional procedures. These data were obtained from 21 radiologists, 41 adult cardiologists and 33 paediatric cardiologists. Average Dose Area Product (DAP) values per procedure were obtained from previous work done in SA. As DAP reflects not only the dose within the radiation field, but also the area of tissue irradiated it is a better indication of scattered radiation which is the source of radiation to the eye. Three categories of modifiers were considered: (1) a reducing modifier accounting for attenuation afforded by the use of ceiling suspended screens and the frequency of use of these screens; (2) a similar modifier for the use of lead glasses and the frequency of use of these glasses; and (3) an escalating modifier for radial (as opposed to femoral) approach and its frequency of use. The maximum modifying factors were taken from published data.
Results: The average number of years worked with fluoroscopy was 12, median 10. The longest was a cardiologist who worked 40 years. The study showed a wide range of estimated eye lens workload exposures (Gy.cm2). Average 354255 ± 675851, median 77418, maximum was a cardiologist 4 320 504, Median for cardiologists 291 346, radiologists 105 680 and paediatricians 35 972. The estimated eye lens workload exposures were not compared to published values, as they are simply a way of assessing which interventionalists receive the greatest exposures to their eyes according to the individual's workload, PPE utilisation and approach. PPE utilisation, specifically ceiling suspended screens, have a large effect on eye exposure, especially for cardiologists, average decrease of 36%. Median before modifiers for cardiologists, radiologist and paediatricians respectively 706 560, 128 579 and 43 245 and after modifiers 291 346, 105 680 and 35 972. Estimated eye workload exposures indicate at least three groups of exposures.
Discussion: There are many factors that influence the scattered exposure to the eyes. This study serves as an indication of the eye exposure received by Interventionalists in SA which could cause cateractogenesis. Another study will compare this data to the cataract findings obtained during lens screening of these same interventionists.
| O-66: Cataract Findings Among South African Interventionalists|| |
A. Rose, W. I. D. Rae1
Departments of Community Health and 1Medial Physics, University of the Free State, Bloemfontein, South Africa. E-mail: [email protected]
Introduction: Ionising radiation is indispensable as a diagnostic, prognostic and therapeutic modality in modern western medicine. Ionising radiation is an established occupational health hazard in the catheterisation laboratory. Exposure may result in health effects such as skin changes, carcinomas, chromosomal aberrations and cataracts. The lenses of the eyes are higher radiosensitive and cataracts in radiation health workers commonly occurs in the posterior capsular (PC) region of the lens. The left eye is often affect up to three times more commonly than the right eye. The dose per procedure varies from 10 to more than 1 000 micro Sievert and depends on the type and duration of the procedure, the skill of the operator and the dose reduction strategies employed (such as personal protective equipment (PPE) used and policies and guidelines followed).
Objectives: The aim of this study was to describe the prevalence of occupational related radiation induced cataracts in South African interventionalists.
Materials and Methods: This study was a cross sectional observational study. The participants were from several different cities in South Africa and were recruited at various conferences. The participants included exposed doctors (interventional radiologists, cardiologists and paediatric cardiologists) and a comparative group of unexposed doctors. All participants completed a survey which collected data on their risk for cataracts, their occupational history, their utilisation of PPE and their training in radiation safety. They had their eyes dilated and had a slit-lamp examination. The data were analysed using STATA 12®. Descriptive and analytical analysis was done. The study received ethical approval from the University of the Free State (UFS44/2014).
Results: There were 351 participants (144 exposed) and 267 (119 exposed) had their eyes screened. The median age was 46.1 (exposed) and 45.5 years (unexposed). There were 89 (72.4%) men and 34 (27.6%) women (exposed). The median years worked was 10 (exposed) and 14 (unexposed). The median years doing fluoroscopic procedures was 9.5 years. The risk factors for cataract included diabetes 5 (4.1%) in exposed and 12 (5.9%) in the unexposed (p=0.473); BMI 25.5 ± 3.5 (exposed), 26.2 ± 4.7 (unexposed); there were two participants that used steroids (unexposed). There were 53 radiologists, 54 adult cardiologists and 37 paediatric cardiologists. In the left eye, there were 34 cataracts (16 in exposed group). In the right eye, there were 25 cataracts (exposed). In the left nucleus, there were 16 opacities (5 in the exposed) and in the right nucleus there were 15 opacities (4 in the exposed). In the left cortex, there were 31 opacities (15 in the exposed). In the right cortex, there were 25 opacities (10 in the exposed group). In the left posterior capsule, there were 11 cataracts, 6 (5.0%) in exposed and 5 (3.4%) in unexposed (p=0.195). In the right posterior capsule, there were 5 cataracts 2 (1.7%) in exposed and 3 (2.0%) in the unexposed (p=0.831). Nuclear and cortical cataracts were the most common which is expected. Cataracts were more common on the left in the exposed.
Discussion: Interventionalists are at increased risk to develop radiation related cataracts. Cortical and nuclear cataract was more common which may be associated with age related changes. The increased prevalence in left side in exposed participants' cataracts suggest an occupational cause. There was a significant difference between exposed and unexposed participants in the posterior capsular category. In conclusion, there should be increased vigilance in radiation protection measures to protect interventionalists from developing cataracts due to ionising radiation exposure.
| O-67: A Prospective Approach of QA in Radiation Oncology and Implementation of AAPM TG 100|| |
D. Banjade, A. Mishra, G. Warr, S. Tan, M. Fuller, R. Hammond, K. Thuraisingam, G. Stevens
Department of Radiation Oncology, Central West Cancer Care Centre, Orange Hospital, New South Wales, Australia. E-mail: [email protected]
Implementation of quality management (QM) system in Radiation Oncology (RO) will improve work efficiency in radiotherapy (RT) and prevent the prospective risk associated in the process. Traditionally, QM in RT has focused on device centric approaches, however, many of the safety and quality issues in RT have been identified as human factors. Therefore, assurance of quality and safety of the department is not only the quality assurance (QA) of the equipment and instruments but also requires implementation of QA programs covering personnel and procedures as a whole.
Founding an interdisciplinary team with full cooperation in the department to focus on mitigating the process-related errors can establish a risk based QM program. Various activities, procedures and work performance can be strengthened by formulating QM systems in RT, emphasizing a proactive response to near misses rather than responding to unacceptable events.
Identifying the likelihood of occurrences, likelihood of failure being undetected and outcome severity of events on the paths of a fault tree analysis (FTA) process can prevent harm to the patient during the RT process. The implementation of total QM approach with procedures, rules and regulations can detect each failure mode on each process and pave the way to deliver safe and quality treatment.
This presentation will review the insights of the AAPM TG-100 QM formalism applied to local processes including error propagation and risk assessment at CWCCC Orange NSW, a regional RT centre in Australia. The QM tool of failure mode and effect analysis (FMEA) and FTA will also be discussed with examples. In addition, the presentation will explore the prospective approach of TG 100 as an integrated QM measure in Radiation Oncology.
| O-68: Performing TG-142 Quality Assurance Procedures on Linear Accelerators Using PIPSpro Software|| |
K. R. Muralidhar, P. Srinivas, K. Jayaram, M. Rambabu, M. Prabhakar, Krishna Komanduri
Department of Radiation Physics, American Oncology Institute, Hyderabad, Telangana, India. E-mail: [email protected]
Introduction: In Radiation Oncology, increase intechnology and treatment techniques made it possible and desirable to perform quality assurance (QA) with increased accuracy. For this Task group-142 (TG-142) from American Association of Physicists in Medicine (AAPM) was developed and published a comprehensive guideline. Recommendations of TG-142 tests are technically challenging both to perform as well to analyze to a high degree of accuracy that the recommendations call for. The objective of this work is to perform and report TG-142 in Linear accelearators using PIPSpro software and phantoms using Electronic Portal Imaging Device (EPID) and KV imager.
Materials and Methods: TG-142 was performed on True beam STx linear accelerator. Imaging is performed using the on board imaging (OBI) and EPID. All monthly and annual TG-142 quality assurance tests were performed and analyzed. Pipspro was designed to be used with portal images. The portal images and KV images in DICOM format were transferred to PIPSpro software for analysis. The tests that were performed were, Imager QA, Radiation light field QA, Star shot image analysis QA with collimator, gantry and table rotation, MLC QA (MLC transmission, MLC position, MLC Multiport test), Stereotactic Test and Image Guided Radiotherapy test.
QC-3 Phantom, supplied by manufacturer was used in Imager QA, for analyzing QA on EPID and OBI images. This test will be useful to observe the changes in performance of EPID and OBI image quality in the long run. For the radiation light field QA, FC-2 phantom was used. Star shot test was performed and Images were obtained from EPID using an equidistant 30 degree angles while rotating collimator, gantry and couch respectively. MLC QA (MLC leaf position, leaf width, and multi-port and leaf transmission) was performed using the MLC phantom on the treatment couch at isocenter by positioning EPID imager at 105 cm SSD. The Stereotactic Module allows the user to perform the Winston-Lutz test. They are 2D and 3D tests that that determines planar radiation-mechanical isocenter offsets and “Optimal Isocenter Shift”. The IGRT module was used to perform QA on positioning/repositioning and imaging and treatment coordinate coincidence on a daily basis with the help of IGRT QA phantom.
Results: All tests gave accurate and reliable resultsand presented in both numerical and graph. In imager QA report, modulation versus Frequency graph obtained and special resolution (line pairs/mm) of F50, F40, F30, Uniformity values that obtained were 0.487, 0.621, 0.755, and 98.305% respectively. In radiation light field displacement, the maximum displacement shown was 0.6 mm and the jaw displacement shown was 0.42 mm respectively. MLC multiporttests have shown that the deviation of leaves in left bank and right bank at various positions (70 mm, 40 mm, 10 mm, -20 mm, -50 mm) were within the tolerance limits (1 mm). Image based MLC QA shown all MLC positions are within 1 mm deviation. MLC Interleaf leakage and interbank leakage were found to be 0.557% and 30.436% respectively. Start shot analysis has shown that the isocenter shift from gantry and collimator was a sphere with 0.29 mm radius. Stereotacticreport had shown a deviation of 0.2, 0.5 and 0.8 mm in x, y and z directions respectively. Positioning and repositioning variations on daily basis were presented in IGRT report.
Conclusion: We performed TG-142 several times repeatedly and at various intervals on True Beam STx and found the performace of the machine is well within tolerance limits protocols. The results are consistent and well within the specifications. We found using PIPSpro istime saving, economical, easy and accurate to perform TG-142 in a busy department.
| O-69: The Application of Texture Analysis for Discrimination Fatty Liver by Ultrasound Images|| |
Akbar Gharbali, Milad Zeinali Kermani
Department of Medical Physics, Urmia University of Medical Sciences, Urmia Iran. E-mail: [email protected]
Introduction: Fatty lever or Hepatic steatosis is an abnormality in excessive accumulation of lipids mainly triglyceride in liver that can cause far reaching metabolic consequences. Early detection and reliable diagnosis of fatty liver increase the cure rate and provide optimal treatment. Ultra-Sonography is a non-invasive and more common and convenient medical imaging to interpret fatty liver. Biopsy has accepted for confirming the ultrasound imaging results. So, it is not possible to demonstrate any significant increase in diagnostic accuracy with conventional way – just visual texture analysis and interpretation of the radiological image.
Objective: To evaluate diagnostic potential of computer aided texture analysis methods in differentiation of fatty liver from normal liver by ultrasound (US) imaging to improve radiologist confidence in identification mild fatty liver with no need for other examination and pathological testing.
Materials and Methods: Database consists of ultrasound images of 35 mild fatty liver and 36 normal liver. By loading ultrasound images in the MaZda software, regions of interests (ROIs) were defined within the fatty liver and normal liver. Gray levels intensity within a ROI normalized according to three normalization schemes:N1: default or original gray level, N2: μ+/- 3 σ (μ= mean and σ= variance), N3: present intensity 1%-99%. Then per ROI per normalization schemes, up to 270 multi scale texture features parameters were computed as descriptors of ROI texture pattern. Then texture features parameters eliminated to the 10 best and most effective features based on applied two algorithms: maximum Fisher Coefficient and or minimum probability of error and average correlation coefficients (POE+ACC). Each ROI within fatty and normal liver US images discriminated by this features data under two standard schemes with three texture analysis methods: PCA (principal Component analysis), LDA (Linear Discriminant analysis) under first nearest neighbor (1-NN) classifier and NDA (Non Linear Discriminant analysis) under artificial neural network (ANN) classifier. The confusion matrix and Receiver Operating Characteristic cure (ROC) analysis were used for examining the discrimination performance of the texture analysis methods under applied options.
Results: The best result for discriminating fatty liver from healthy liver was related to NDA texture analysis method with sensitivity, specificity and area under the EOC cure of %99, %98 and 0.98 respectively.
Discussions: Our result indicate that automated texture analysis is a reliable and powerful method for discriminating fatty liver from normal liver tissue in ultrasound images. So, it has the potential to boost the radiologist's accuracy and therefore confidence for effective use in differentiation of fatty liver on liver US image.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16]
[Table 1], [Table 2], [Table 3], [Table 4]