Shiraz University of Medical SciencesJournal of Biomedical Physics and Engineering2251-72005120150301Editorial43178ENARMehdizadeh0000-0002-2867-7887Journal Article20150415Shiraz University of Medical SciencesJournal of Biomedical Physics and Engineering2251-72005120150301Effect of Gold Nanoparticles on Prostate Dose Distribution under Ir-192 Internal and 18 MV External Radiotherapy Procedures Using Gel Dosimetry and Monte Carlo Method43179ENHKhosraviTarbiat Modares UniversityBHashemiTarbiat Modares University0000-0002-2511-4376S RMahdaviIrani University of Medical Sciences0000-0003-1973-2140PHejaziSemnan University of Medical SciencesJournal Article20141128Background: Gel polymers are considered as new dosimeters for determining radiotherapy dose distribution in three dimensions.Objective: The ability of a new formulation of MAGIC-f polymer gel was assessed by experimental measurement and Monte Carlo (MC) method for studying the effect of gold nanoparticles (GNPs) in prostate dose distributions under the internal Ir-192 and external 18MV radiotherapy practices.Method: A Plexiglas phantom was made representing human pelvis. The GNP shaving 15 nm in diameter and 0.1 mM concentration were synthesized using chemical reduction method. Then, a new formulation of MAGIC-f gel was synthesized. The fabricated gel was poured in the tubes located at the prostate (with and without the GNPs) and bladder locations of the phantom. The phantom was irradiated to an Ir-192 source and 18 MV beam of a Varian linac separately based on common radiotherapy procedures used for prostate cancer. After 24 hours, the irradiated gels were read using a Siemens 1.5 Tesla MRI scanner. The absolute doses at the reference points and isodose curves resulted from the experimental measurement of the gels and MC simulations following the internal and external radiotherapy practices were compared. Results: The mean absorbed doses measured with the gel in the presence of the GNPs in prostate were 15% and 8 % higher than the corresponding values without the GNPs under the internal and external radiation therapies, respectively. MC simulations also indicated a dose increase of 14 % and 7 % due to presence of the GNPs, for the same experimental internal and external radiotherapy practices, respectively. Conclusion: There was a good agreement between the dose enhancement factors (DEFs) estimated with MC simulations and experiment gel measurements due to the GNPs. The results indicated that the polymer gel dosimetry method as developed and used in this study, can be recommended as a reliable method for investigating the DEF of GNPs in internal and external radiotherapy practices.   Shiraz University of Medical SciencesJournal of Biomedical Physics and Engineering2251-72005120150301Effect of Tissue Composition on Dose Distribution in Electron Beam Radiotherapy43180ENMGhorbaniMedical Physics Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran0000-0001-5518-8870Z STabatabaeiMedical Physics Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, IranAVejdani NoghreiyanMedical Physics Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, IranHVosoughiMedical Physics Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, IranCKnaupComprehensive Cancer Centers of Nevada, Las Vegas, Nevada, USAJournal Article20141228Objective: The aim of this study is to evaluate the effect of tissue composition on dose distribution in electron beam radiotherapy.Methods: A Siemens Primus linear accelerator and a phantom were simulated using MCNPX Monte Carlo code. In a homogeneous cylindrical phantom, six types of soft tissue and three types of tissue-equivalent materials were investigated. The tissues included muscle (skeletal), adipose tissue, blood (whole), breast tissue, soft tissue (9-components) and soft tissue (4-component). The tissue-equivalent materials were water, A-150 tissue-equivalent plastic and perspex. Electron dose relative to dose in 9-component soft tissue at various depths on the beam’s central axis was determined for 8, 12, and 14 MeV electron energies.Results: The results of relative electron dose in various materials relative to dose in 9-component soft tissue were reported for 8, 12 and 14 MeV electron beams as tabulated data. While differences were observed between dose distributions in various soft tissues and tissue-equivalent materials, which vary with the composition of material, electron energy and depth in phantom, they can be ignored due to the incorporated uncertainties in Monte Carlo calculations. Conclusion: Based on the calculations performed, differences in dose distributions in various soft tissues and tissue-equivalent materials are not significant. However, due to the difference in composition of various materials, further research in this field with lower uncertainties is recommended. Shiraz University of Medical SciencesJournal of Biomedical Physics and Engineering2251-72005120150301Accuracy Evaluation of Oncentraâ„¢ TPS in HDR Brachytherapy of Nasopharynx Cancer Using EGSnrc Monte Carlo Code43181ENKHadadShiraz University0000-0003-4495-0350MZohrevandShiraz UniversityRFaghihiShiraz UniversityASedighi PashakiMahdieh M.R.I Center, HamedanJournal Article20141215Background: HDR brachytherapy is one of the commonest methods of nasopharyngeal cancer treatment. In this method, depending on how advanced one tumor is, 2 to 6 Gy dose as intracavitary brachytherapy is prescribed. Due to high dose rate and tumor location, accuracy evaluation of treatment planning system (TPS) is particularly important. Common methods used in TPS dosimetry are based on computations in a homogeneous phantom. Heterogeneous phantoms, especially patient-specific voxel phantoms can increase dosimetric accuracy.Materials and Methods: In this study, using CT images taken from a patient and ctcreate-which is a part of the DOSXYZnrc computational code, patient-specific phantom was made. Dose distribution was plotted by DOSXYZnrc and compared with TPS one. Also, by extracting the voxels absorbed dose in treatment volume, dose-volume histograms (DVH) was plotted and compared with Oncentraâ„¢ TPS DVHs.Results: The results from calculations were compared with data from Oncentraâ„¢ treatment planning system and it was observed that TPS calculation predicts lower dose in areas near the source, and higher dose in areas far from the source relative to MC code. Absorbed dose values in the voxels also showed that TPS reports D90 value is 40% higher than the Monte Carlo method.Conclusion: Today, most treatment planning systems use TG-43 protocol. This protocol may results in errors such as neglecting tissue heterogeneity, scattered radiation as well as applicator attenuation. Due to these errors, AAPM emphasized departing from TG-43 protocol and approaching new brachytherapy protocol TG-186 in which patient-specific phantom is used and heterogeneities are affected in dosimetry. Shiraz University of Medical SciencesJournal of Biomedical Physics and Engineering2251-72005120150301Evaluation of Electron Contamination in Cancer Treatment with Megavoltage Photon Beams: Monte Carlo Study43182ENFSeifArak University of Medical SciencesM RBayatianiArak University of Medical SciencesJournal Article20141007Background: Megavoltage beams used in radiotherapy are contaminated with secondary electrons. Different parts of linac head and air above patient act as a source of this contamination. This contamination can increase damage to skin and subcutaneous tissue during radiotherapy. Monte Carlo simulation is an accurate method for dose calculation in medical dosimetry and has an important role in optimization of linac head materials. The aim of this study was to calculate electron contamination of Varian linac.Materials and Method: The 6MV photon beam of Varian (2100 C/D) linac was simulated by Monte Carlo code, MCNPX, based on its company’s instructions. The validation was done by comparing the calculated depth dose and profiles of simulation with dosimetry measurements in a water phantom (error less than 2%). The Percentage Depth Dose (PDDs), profiles and contamination electron energy spectrum were calculated for different therapeutic field sizes (5×5 to 40×40 cm2) for both linacs. Results: The dose of electron contamination was observed to rise with increase in field size. The contribution of the secondary contamination electrons on the surface dose was 6% for 5×5 cm2 to 27% for 40×40 cm2, respectively. Conclusion: Based on the results, the effect of electron contamination on patient surface dose cannot be ignored, so the knowledge of the electron contamination is important in clinical dosimetry. It must be calculated for each machine and considered in Treatment Planning Systems. Shiraz University of Medical SciencesJournal of Biomedical Physics and Engineering2251-72005120150301Investigation of Collimator Influential Parameter on SPECT Image Quality: a Monte Carlo Study43183ENShBanari BahnamiriJournal Article20141230Background: Obtaining high quality images in Single Photon Emission Tomography (SPECT) device  is the most important goal in nuclear medicine. Because if image quality is low, the possibility of making a mistake in diagnosing and treating the patient will rise. Studying effective factors in spatial resolution of imaging systems is thus deemed to be vital. One of the most important factors in SPECT imaging in nuclear medicine is the use of an appropriate collimator for a certain radiopharmaceutical feature in order to create the best image as it can be effective in the quantity of Full Width at Half Maximum (FWHM) which is the main parameter  in spatial resolution.Method: In this research, the simulation of the detector and collimator of SPECT imaging device, Model HD3 made by Philips Co. and the investigation of important factors on the collimator were carried out using MCNP-4c code.Results: The results of the experimental measurments and simulation calculations revealed a relative difference of less than 5% leading to the confirmation of the accuracy of conducted simulation MCNP code calculation. Conclusion: This is the first essential step in the design and modelling of new collimators used for creating high quality images in nuclear medicine.Â