Journal of Medical Physics
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   2013| January-March  | Volume 38 | Issue 1  
    Online since January 29, 2013

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Dosimetric evaluation of Acuros XB dose calculation algorithm with measurements in predicting doses beyond different air gap thickness for smaller and larger field sizes
Suresh Rana, Kevin Rogers
January-March 2013, 38(1):9-14
DOI:10.4103/0971-6203.106600  PMID:23532180
In this study, dose prediction accuracy of Acuros XB (AXB) dose calculation algorithm beyond air gap thickness (range 2, 4, and 6 cm) in simple inhomogeneous phantoms was investigated. The evaluation of AXB was performed by comparing the doses calculated by AXB with the doses calculated by Anisotropic Analytical Algorithm (AAA) and the measured data for different field sizes (3 × 3, 5 × 5, and 10 × 10 cm 2 ) of a 6 MV photon beam. The dose computation was performed within Eclipse treatment planning system, and measurements were acquired with a cylindrical ionization chamber. Central axis depth dose comparisons were done in solid-water material region up to 5 cm distance from air/solid-water interface. The results of AXB had better agreement with measurements at all measured points than that of AAA. The discrepancies between AXB and measured data were seen from − 3.81% to + 0.9%, whereas the AAA differences with measurement from − 3.1% to − 10.9%. The combination of the smallest test field size and the largest air gap produced the highest range (1-5 cm distance from air/solid-water interface) in dose difference (AAA: −4.0% to − 10.6% and AXB: −3.8% to + 0.6%). The AAA computational time was about 8 times faster than that of AXB. In conclusion, AXB is more appropriate to use for dose predictions, especially when low-density heterogeneities are involved.
  14,147 700 22
Dosimetric comparison of intensity modulated radiotherapy isocentric field plans and field in field (FIF) forward plans in the treatment of breast cancer
Zakiya Salem Al-Rahbi, Zahid Al Mandhari, Ramamoorthy Ravichandran, Fatma Al-Kindi, Cheriyathmanjiyil Antony Davis, Saju Bhasi, Namrata Satyapal, Balakrishnan Rajan
January-March 2013, 38(1):22-29
The present study is aimed at comparing the planning and delivery efficiency between three-dimensional conformal radiotherapy (3D-CRT), field-in-field, forward planned, intensity modulated radiotherapy (FIF-FP-IMRT), and inverse planned intensity modulated radiotherapy (IP-IMRT). Treatment plans of 20 patients with left-sided breast cancer, 10 post-mastectomy treated to a prescribed dose of 45 Gy to the chest wall in 20 fractions, and 10 post-breast-conserving surgery to a prescribed dose of 50 Gy to the whole breast in 25 fractions, with 3D-CRT were selected. The FiF-FP-IMRT plans were created by combining two open fields with three to four segments in two tangential beam directions. Eight different beam directions were chosen to create IP-IMRT plans and were inversely optimized. The homogeneity of dose to planning target volume (PTV) and the dose delivered to heart and contralateral breast were compared among the techniques in all the 20 patients. All the three radiotherapy techniques achieved comparable radiation dose delivery to PTV-95% of the prescribed dose covering > 95% of the breast PTV. The mean volume of PTV receiving 105% (V 105 ) of the prescribed dose was 1.7% (range 0-6.8%) for IP-IMRT, 1.9% for FP-IMRT, and 3.7% for 3D-CRT. The homogeneity and conformity indices (HI and CI) were similar for 3D-CRT and FP-IMRT, whereas the IP-IMRT plans had better conformity index at the cost of less homogeneity. The 3D-CRT and FiF-FP-IMRT plans achieved similar sparing of critical organs. The low-dose volumes (V 5Gy ) in the heart and lungs were larger in IP-IMRT than in the other techniques. The value of the mean dose to the ipsilateral lung was higher for IP-IMRT than the values for with FiF-FP-IMRT and 3D-CRT. In the current study, the relative volume of contralateral breast receiving low doses (0.01, 0.6, 1, and 2Gy) was significantly lower for the FiF-FP-IMRT and 3D-CRT plans than for the IP-IMRT plan. Compared with 3D-CRT and IP-IMRT, FiF-FP-IMRT proved to be a simple and efficient planning technique for breast irradiation. It provided dosimetric advantages, significantly reducing the size of the hot spot and minimally improving the coverage of the target volume. In addition, it was felt that FiF-FP-IMRT required less planning time and easy field placements.
  10,451 439 1
Peripheral dose measurements with diode and thermoluminescence dosimeters for intensity modulated radiotherapy delivered with conventional and un-conventional linear accelerator
Rajesh Kinhikar, Poonam Gamre, Chandrashekhar Tambe, Sudarshan Kadam, George Biju, Suryaprakash , CS Magai, Dipak Dhote, Shyam Shrivastava, Deepak Deshpande
January-March 2013, 38(1):4-8
DOI:10.4103/0971-6203.106599  PMID:23531765
The objective of this paper was to measure the peripheral dose (PD) with diode and thermoluminescence dosimeter (TLD) for intensity modulated radiotherapy (IMRT) with linear accelerator (conventional LINAC), and tomotherapy (novel LINAC). Ten patients each were selected from Trilogy dual-energy and from Hi-Art II tomotherapy. Two diodes were kept at 20 and 25 cm from treatment field edge. TLDs (LiF:MgTi) were also kept at same distance. TLDs were also kept at 5, 10, and 15 cm from field edge. The TLDs were read with REXON reader. The readings at the respective distance were recorded for both diode and TLD. The PD was estimated by taking the ratio of measured dose at the particular distance to the prescription dose. PD was then compared with diode and TLD for LINAC and tomotherapy. Mean PD for LINAC with TLD and diode was 2.52 cGy (SD 0.69), 2.07 cGy (SD 0.88) at 20 cm, respectively, while at 25 cm, it was 1.94 cGy (SD 0.58) and 1.5 cGy (SD 0.75), respectively. Mean PD for tomotherapy with TLD and diode was 1.681 cGy SD 0.53) and 1.58 (SD 0.44) at 20 cm, respectively. The PD was 1.24 cGy (SD 0.42) and 1.088 cGy (SD 0.35) at 25 cm, respectively, for tomotherapy. Overall, PD from tomotherapy was found lower than LINAC by the factor of 1.2-1.5. PD measurement is essential to find out the potential of secondary cancer. PD for both (conventional LINAC) and novel LINACs (tomotherapy) were measured and compared with each other. The comparison of the values for PD presented in this work and those published in the literature is difficult because of the different experimental conditions. The diode and TLD readings were reproducible and both the detector readings were comparable.
  4,549 320 3
Evaluating the effect of ultrasmall superparamagnetic iron oxide nanoparticles for a long-term magnetic cell labeling
Saeed Shanehsazzadeh, Mohammad Ali Oghabian, Barry J Allen, Massoud Amanlou, Afshin Masoudi, Fariba Johari Daha
January-March 2013, 38(1):34-40
DOI:10.4103/0971-6203.106603  PMID:23531682
In order to evaluate the long-term viability, the iron content stability, and the labeling efficiency of mammalian cells using magnetic cell labeling; dextran-coated ultrasmall superparamagnetic iron oxide (USPIOs) nanoparticles with plain surfaces having a hydrodynamic size of 25 nm were used for this study. Tests were carried out in four groups each containing 5 flasks of 5.5 × 10 6 AD-293 embryonic kidney cells. The cell lines were incubated for 24 h using four different iron concentrations with and without protamine sulfate (Pro), washed with phosphate-buffered saline (PBS) and centrifuged three times to remove the unbounded USPIOs. Cell viability was also verified using USPIOs. There were no significant differences in the cell viability between the control group of cells and those groups with iron uptake at the specified iron concentrations. The average iron uptake ratio compared to that of the control group was (114 ± 1). The magnetic resonance images (MRI) at post-labeling day 1 and day 21 showed (75 ± 4)% and (22 ± 5)% signal decrements compared to that of the control, respectively. The Perl's Prussian blue test showed that 98% of the cells were labeled, and the iron concentration within the media did not affect the cell iron uptake. Magnetic cellular labeling with the USPIO-Pro complex had no short or medium term (3 weeks) toxic effects on AD-293 embryonic kidney cells.
  4,588 146 8
Evaluation of target dose based on water-equivalent thickness in external beam radiotherapy
Behnaz Ghanbar Moghaddam, Masoud Vahabi-Moghaddam, Alireza Sadremomtaz
January-March 2013, 38(1):44-51
DOI:10.4103/0971-6203.106605  PMID:23532059
In vivo dosimetry was carried out for 152 patients receiving external beam radiotherapy and the treatment sites were divided into two main groups: Thorax, Abdomen, and Pelvic (120 fields) and Head and Neck (52 fields). Combined entrance and exit dose measurements were performed using LiF: Mg, Cu, P thermoluminescent dosimeters (TLDs). Water-equivalent (effective) thicknesses and target dose were evaluated using dose transmission data. The ratio of measured to expected value for each quantity was considered as an indicator for the accuracy of the parameter. The average ratio of the entrance dose was evaluated as 1.01 ± 0.07. In the diameter measurement, the mean ratio of effective depth divided by the contour depth is 1.00 ± 0.13 that shows a wide distribution which reflects the influence of contour inaccuracies as well as tissue inhomogeneities. At the target level, the mean ratio of measured to the prescribed dose is 1.00 ± 0.07. According to our findings, the difference between effective depth and patient depth has a direct relation to target dose discrepancies. There are some inevitable sources which may cause the difference. Evaluation and application of effective diameter in treatment calculations would lead to a more reliable target dose, especially for fields which involve Thorax, Abdomen, and Pelvic.
  4,509 214 2
Monte Carlo N Particle code - Dose distribution of clinical electron beams in inhomogeneous phantoms
HA Nedaie, MA Mosleh-Shirazi, M Allahverdi
January-March 2013, 38(1):15-21
DOI:10.4103/0971-6203.106607  PMID:23533162
Electron dose distributions calculated using the currently available analytical methods can be associated with large uncertainties. The Monte Carlo method is the most accurate method for dose calculation in electron beams. Most of the clinical electron beam simulation studies have been performed using non- MCNP [Monte Carlo N Particle] codes. Given the differences between Monte Carlo codes, this work aims to evaluate the accuracy of MCNP4C-simulated electron dose distributions in a homogenous phantom and around inhomogeneities. Different types of phantoms ranging in complexity were used; namely, a homogeneous water phantom and phantoms made of polymethyl methacrylate slabs containing different-sized, low- and high-density inserts of heterogeneous materials. Electron beams with 8 and 15 MeV nominal energy generated by an Elekta Synergy linear accelerator were investigated. Measurements were performed for a 10 cm × 10 cm applicator at a source-to-surface distance of 100 cm. Individual parts of the beam-defining system were introduced into the simulation one at a time in order to show their effect on depth doses. In contrast to the first scattering foil, the secondary scattering foil, X and Y jaws and applicator provide up to 5% of the dose. A 2%/2 mm agreement between MCNP and measurements was found in the homogenous phantom, and in the presence of heterogeneities in the range of 1-3%, being generally within 2% of the measurements for both energies in a "complex" phantom. A full-component simulation is necessary in order to obtain a realistic model of the beam. The MCNP4C results agree well with the measured electron dose distributions.
  4,191 239 1
The assessment of cytotoxic T cell and natural killer cells activity in residents of high and ordinary background radiation areas of Ramsar-Iran
Sajad Borzoueisileh, Ali Shabestani Monfared, Saeid Abediankenari, Amrollah Mostafazadeh
January-March 2013, 38(1):30-33
DOI:10.4103/0971-6203.106602  PMID:23531635
The effective radiation dose of human from natural sources is about 2.4 mSv/y and the dose limit for radiation workers is 20 mSv/y. Ramsar, a city in Iran, has been the subject of concern in the last forty years for a high level of radiation measured in some spots as high as 260 mSv/y. Carcinogenesis is one of the most studied effects of radiation especially in high doses. Recent studies showed that the high level of natural radiation received by inhabitants of this area, paradoxically don't have significant health effect. Natural killer (NK) cells and cytotoxic T cells are the most important cells in tumor immune surveillance and CD107a is a widely expressed intracellular protein located in the lysosomal/endosomal membrane. CD107a transiently located on the cell membrane can be used as a marker of CD8 + T cell degranulation following stimulation. It is also expressed, to a lower extent, on activated NK cells. In this study, 60 healthy people were selected randomly and their consent obtained and confounding factors such as sex, age, life-styles was matched then the count of activated NK and CD8 + cells was compared in high and normal background radiation areas inhabitants of Ramsar. After filling the questionnaire and measurement of background radiation, blood samples of 30 healthy people from each region were analyzed immediately by means of flowcytometry. The leukocytes and their subsets were not significantly different between two groups and the count of active cells was higher in control group. The result shows that the changes in immune system occur due to radiation and maybe it is as a result of higher radiosensitivity of activated cells.
  3,604 162 3
Uncertainty concerning the 4-field box technique for Stage-IB2 carcinoma of the uterine cervix
Priyanka Thakur, Swaroop Revannasiddaiah, Madhup Rastogi, Manoj Kumar Gupta, Rajeev Kumar Seam, Manish Gupta
January-March 2013, 38(1):41-43
DOI:10.4103/0971-6203.106604  PMID:23531883
Radiation Therapy (RT) plays a pivotal role in the curative approach for carcinoma of the cervix. Inspite of the emergence of various new conformal techniques in RT, conventional techniques still hold vital importance. Majority of the patients worldwide are treated with 2D-RT techniques. 2D-RT techniques have been proven to be non-inferior and simpler in comparison to 3D-RT in the context of carcinoma of the cervix. However, inadequate target volume coverage with improper portal design can preclude the chances of cure. We demonstrate the need for abolishing guesswork in terms of target volume determination through the example of a patient's sagittal magnetic resonance image showing a case of the retroverted uterus which would have been likely to be missed from the treatment portals if they were designed using definitions based on bony landmarks.
  3,221 171 2
Software safety in radiation therapy
Greg Salomons, Diane Kelly
January-March 2013, 38(1):1-3
DOI:10.4103/0971-6203.106592  PMID:23533316
  2,840 158 -
News and Events
Tharmarnadar Ganesh
January-March 2013, 38(1):52-55
  1,848 117 -
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