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Bahreyni Toossi M.T.,Mashhad University of Medical Sciences | Abdollahi M.,Mashhad University of Medical Sciences | Abdollahi M.,Reza Radiation Oncology Center | Ghorbani M.,North Khorasan University of Medical Sciences
Reports of Practical Oncology and Radiotherapy | Year: 2013

Aim: Stepping source in brachytherapy systems is used to treat a target lesion longer than the effective treatment length of the source. Cancerous lesions in the cervix, esophagus and rectum are examples of such a target lesion. Background: In this study, the stepping source of a GZP6 afterloading intracavitary brachytherapy unit was simulated using Monte Carlo (MC) simulation and the results were used for the validation of the GZP6 treatment planning system (TPS). Materials and methods: The stepping source was simulated using MCNPX Monte Carlo code. Dose distributions in the longitudinal plane were obtained by using a matrix shift method for esophageal tumor lengths of 8 and 10cm. A mesh tally has been employed for the absorbed dose calculation in a cylindrical water phantom. A total of 5×108 photon histories were scored and the MC statistical error obtained was at the range of 0.008-3.5%, an average of 0.2%. Results: The acquired MC and TPS isodose curves were compared and it was shown that the dose distributions in the longitudinal plane were relatively coincidental. In the transverse direction, a maximum dose difference of 7% and 5% was observed for tumor lengths of 8 and 10. cm, respectively. Conclusion: Considering that the certified source activity is given with ±10% uncertainty, the obtained difference is reasonable. It can be concluded that the accuracy of the dose distributions produced by GZP6 TPS for the stepping source is acceptable for its clinical applications. © 2012 Greater Poland Cancer Centre. Source


Bahreyni Toosi M.T.,Mashhad University of Medical Sciences | Mohamadian N.,Mashhad University of Medical Sciences | Ghorbani M.,Mashhad University of Medical Sciences | Khorshidi F.,Mashhad University of Medical Sciences | And 2 more authors.
Journal of Biomedical Physics and Engineering | Year: 2016

Objective: Radiochromic EBT3 film is a later generation of radiochromic films. The aim of this study is to compare EBT and EBT3 radiochromic films in radiotherapy fields of breast cancer. Methods: A RANDO phantom was irradiated by a 6 MV Siemens Primus linac with medial and lateral fields of radiotherapy of breast cancer. Dosimetry was performed in various points in the fields using EBT and EBT3 films. Films were scanned by a Microtek color scanner. Dose values from two films in corresponding points were compared. Results: In the investigation of calibration, net optical density (NOD) of EBT radiochromic is more than the EBT3 radiochromic film. The highest percentage difference between NODs of two films is related to 0.75 Gy and equals to 14.19%. The lowest value is related to 0.2 Gy dose and is equal to 3.31%. The highest percentage difference between two films on the RANDO phantom in breast cancer fields is 13.51% and the minimum value is equal to 0.33%. Conclusion: From the comparison between the two films, most of the points show differences in dose in the measurements in fields of breast cancer radiotherapy. These differences are attributed to the thickness of the active layers, the overall thickness of the films, and the difference in the calibration fitted functions. The advantage of EBT film over EBT3 is a higher sensitivity; on the other hand EBT3 film allows to use its both sides in the scanning process and it is a new version of this film type. © 2016, Shiraz University of Medical Sciences. All rights reserved. Source


Bahreyni Toossi M.T.,Mashhad University of Medical Sciences | Ghorbani M.,Mashhad University of Medical Sciences | Akbari F.,Reza Radiation Oncology Center | Sabet L.S.,Mashhad University of Medical Sciences | Mehrpouyan M.,Sabzevar University of Medical science
Journal of Radiotherapy in Practice | Year: 2013

Background Electron mode is used for treatment of superficial tumours in linac-based radiotherapy. Purpose The aim of present study is simulation of 8, 12 and 14 MeV electrons from a Siemens Primus linac using MCNPX Monte Carlo (MC) code and verification of the results based on comparison of the results with the measured data. Materials and methods Electron mode for 8, 12 and 14 MeV electron energies of a Siemens Primus linac was simulated using MCNPX MC code. Percent depth dose (PDD) data for 10 × 10, 15 × 15 and 25 × 25 cm2 applicators obtained from MC simulations were compared with the corresponding measured data. Results Gamma index values were less than unity in most of points for all the above-mentioned energies and applicators. However, for 25 × 25 cm2 applicator in 8 MeV energy, 10 × 10 cm2 applicator and 15 × 15 cm2 applicator in 14 MeV energy, there were four data points with gamma indices higher than unity. However among these data points, there are a number of cases with relatively large value of gamma index, these cases are positioned on the bremsstrahlung tail of the PDD curve which is not normally used in treatment planning. Conclusion There was good agreement between the results of MC simulations developed in this study and the measured values. The obtained simulation programmes can be used in dosimetry of electron mode of Siemens Primus linac in the cases in which it is not easily feasible to perform experimental in-phantom measurements. Copyright © Cambridge University Press 2013. Source


Soleymanifard S.,Mashhad University of Medical Sciences | Toossi M.T.B.,Mashhad University of Medical Sciences | Khosroabadi M.,North Khorasan University of Medical Sciences | Noghreiyan A.V.,Mashhad University of Medical Sciences | And 2 more authors.
Australasian Physical and Engineering Sciences in Medicine | Year: 2014

Skin dose assessment for radiotherapy patients is important to ensure that the dose received by skin is not excessive and does not cause skin reactions. Immobilizing casts may have a buildup effect, and can enhance the skin dose. This study has quantified changes to the surface dose as a result of head and neck immobilizing casts. Medtech and Renfu casts were stretched on the head of an Alderson Rando-Phantom. Irradiation was performed using 6 and 15 MV X-rays, and surface dose was measured by thermoluminescence dosimeters. In the case of 15MV photons, immobilizing casts had no effect on the surface dose. However, the mean surface dose increase reached up to 20 % when 6MV X-rays were applied. Radiation incidence angle, thickness, and meshed pattern of the casts affected the quantity of dose enhancement. For vertical beams, the surface dose increase was more than tangential beams, and when doses of the points under different areas of the casts were analysed separately, results showed that only doses of the points under the thick area had been changed. Doses of the points under the thin area and those within the holes were identical to the same points without immobilizing casts. Higher dose which was incurred due to application of immobilizing casts (20 %) would not affect the quality of life and treatment of patients whose head and neck are treated. Therefore, the benefits of head and neck thermoplastic casts are more than their detriments. However, producing thinner casts with larger holes may reduce the dose enhancement effect. © 2014, Australasian College of Physical Scientists and Engineers in Medicine. Source


Bahreyni Toossi M.T.,Mashhad University of Medical Sciences | Ghorbani M.,Mashhad University of Medical Sciences | Akbari F.,Reza Radiation Oncology Center | Mehrpouyan M.,Sabzevar University of Medical science | Sobhkhiz Sabet L.,Reza Radiation Oncology Center
Australasian Physical and Engineering Sciences in Medicine | Year: 2015

The aim of this study is to evaluate the effect of tooth and dental restoration materials on electron dose distribution and photon contamination production in electron beams of a medical linac. This evaluation was performed on 8, 12 and 14 MeV electron beams of a Siemens Primus linac. MCNPX Monte Carlo code was utilized and a 10 × 10 cm2 applicator was simulated in the cases of tooth and combinations of tooth and Ceramco C3 ceramic veneer, tooth and Eclipse alloy and tooth and amalgam restoration materials in a soft tissue phantom. The relative electron and photon contamination doses were calculated for these materials. The presence of tooth and dental restoration material changed the electron dose distribution and photon contamination in phantom, depending on the type of the restoration material and electron beam’s energy. The maximum relative electron dose was 1.07 in the presence of tooth including amalgam for 14 MeV electron beam. When 100.00 cGy was prescribed for the reference point, the maximum absolute electron dose was 105.10 cGy in the presence of amalgam for 12 MeV electron beam and the maximum absolute photon contamination dose was 376.67 μGy for tooth in 14 MeV electron beam. The change in electron dose distribution should be considered in treatment planning, when teeth are irradiated in electron beam radiotherapy. If treatment planning can be performed in such a way that the teeth are excluded from primary irradiation, the potential errors in dose delivery to the tumour and normal tissues can be avoided. © 2015 Australasian College of Physical Scientists and Engineers in Medicine Source

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