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Implementation of a modern treatment technique, such as IMRT, has been improved. In line with that, Monte Carlo (MC) simulations of this technique require the ability of complex beam configurations modelling with respect to the patient. The source 20 DOSXYZnrc with the dynamic and step and shoot technique can be used to simulate the modality. However, they have a different process to obtain the dose distribution in a certain phantom. This study aimed to compare the simulation efficiency and isodose dose distribution in a water phantom from various beam angles and multileaf collimator (MLC) positions in an IMRT plan using source 20. The 30 × 30 × 30 cm3 phantom was irradiated by Varian Clinac iX10MV photon beam with various field sizes from 2 × 2 to 6 × 6 cm2 using some beam angles 5°, 30°, 90°, 180°, and 300° and maintaining the source to surface distance (SSD) of 100 cm. The field-by-field and five-field methods were used to obtain the 3-dimensional (3D) dose distribution. The dose distribution of these methods was compared using the gamma index, DVH analysis, and simulation efficiency. Higher efficiency is better because it implies that it takes less time to reach a given uncertainty. The implementation of source 20 has been validated, with similar results, with validated source in DOSXYZnrc. The identical 3D-dimensions dose distributions using source 20 for dynamic and step and shoot were observed. Two simulations used the same number of histories with the statistical uncertainty of less than 3%. The step and shoot technique was more efficient than the dynamic simulation.

AIM: This study aimed to commission the Elekta Infinity™ working in 6 and 10 MV photon beam installed in Concord International Hospital, Singapore, and compare the OFs between MC simulation and measurement using PTW semiflex and microDiamond detector for small field sizes. MATERIAL AND METHODS: There are two main steps in this study: modelling of Linac 6 and 10 MV photon beam and analysis of the output factors for field size 2 × 2–10 × 10 cm(2). The EGSnrc/BEAMnrc-DOSXYZnrc code was used to model and characterize the Linac and to calculate the dose distributions in a water phantom. The dose distribution and OFs were compared to the measurement data in the same condition. RESULTS: The commissioning process was only conducted for a 10 × 10 cm(2) field size. The PDD obtained from MC simulation showed a good agreement with the measurement. The local dose difference of PDDs was less than 2% for 6 and 10 MV. The initial electron energy was 5.2 and 9.4 MeV for 6 and 10 MV photon beam, respectively. This Linac model can be used for dose calculation in other situations and different field sizes because this Linac has been commissioned and validated using Monte Carlo simulation. The 10 MV Linac produces higher electron contamination than that of 6 MV. CONCLUSIONS: The Linac model in this study was acceptable. The most important result in this work comes from OFs resulted from MC calculation. This value was more significant than the OFs from measurement using semiflex and microDiamond for all beam energy and field sizes because of the CPE phenomenon.

This research aims to study one of the radiotherapy techniques of VMAT and calculate the dose distribution on phantom cylinders using the Monte Carlo EGSnrc method. VMAT is one of radiotherapy technique where is all the fractions of the dose are given continuously when the gantry rotates around the patient with manages gantry rotation speed, MLC leaf position and the dose fraction is given. The simulation process begins with head linac modeling using BEAMnrc, and using the Monte Carlo VMAT simulation uses DOSXYZnrc software. The parameters for the BEAMnrc and DOSXYZnrc simulations using information from DICOM data set rtplan AAA are read using the pycom code. The results of this study provide information about the characteristics of 6 MV photon files such as fluence, fluence energy, spectral distribution, and fluence energy distribution, and dose distribution in phantom cylinders. The VMAT Monte Carlo simulation was carried out using 300 million particles which resulted in a VMAT dose distribution in the form of a dose profile curve and an isodose curve, the result shows that the curve of VMAT simulation using phantom cylinders produced the maximum dose distribution in the isocenter

CUDA EGS was CUDA implementation to simulate transport photon in a material based on Monte Carlo algorithm for X-ray imaging. The objective of this study was to investigate the effect of inhomogeneities in inhomogeneity phantom for small field dosimetry (1×1, 2×2, 3×3, 4×4 and 5×5 cm2). Two phantoms, homogeneity and inhomogeneity phantom were used. The interaction in homogeneity and inhomogeneity phantom was dominated by Compton interaction and multiple scattering. The CUDA EGS can represent the inhomogeneity effect in small field dosimetry by combining the grayscale curve between homogeneity and inhomogeneity phantom. The grayscale curve in inhomogeneity phantom is not asymmetric because of the existence of different material in phantom.

The purpose of this study was to investigate the characteristics of electron contamination and Output Factors (OFs) from Varian Trilogy Clinac iX 6 MV photon beam at small field sizes. EGSnrc Monte Carlo (MC) code system was used to model the photon beam for this Linear Accelerator (Linac) head and analyze the electron contamination and OFs from this treatment head. The electron contamination was analyzed for field sizes of 1 × 1, 2 × 2, 3 × 3, 4 × 4, and 5 × 5 cm2. The number of electron contamination increases with increasing field sizes, but the maximum energy of the electron contamination stays constant (at around 1.87 MeV for each field size). The contaminants contribute to the dose at the surface of the water phantom (1–5 cm from the surface) for field size 4 × 4 and 5 × 5 cm2 and this dose decreases with depth. The OFs are simulated by EGSnrc code system and have a good agreement with measurement (deviation 3.45, 1.76, and 0.86 for field of 2, 3 and 4, respectively). This study presented that MC methods have great potential to accurately predict the electron contamination and OFs for 6 MV photon beam. Published version

Treatment fields consist of tissue other than water equivalent tissue (soft tissue, bones, lungs, etc.). The inhomogeneity effect can be investigated by Monte Carlo (MC) simulation. MC simulation of the radiation transport in an absorbing medium is the most accurate method for dose calculation in radiotherapy. The aim of this work is to evaluate the effect of inhomogeneity phantom on dose calculations in photon beam radiotherapy obtained by different MC codes. MC code system EGSnrc and Geant4 was used in this study. Inhomogeneity phantom dimension is 39.5 × 30.5 × 30 cm3 and made of 4 material slices (12.5 cm water, 10 cm aluminium, 5 cm lung and 12.5 cm water). Simulations were performed for field size 4 × 4 cm2 at SSD 100 cm. The spectrum distribution Varian Trilogy Clinac iX 10 MV was used. Percent depth dose (PDD) and dose profile was investigated in this research. The effects of inhomogeneities on radiation dose distributions depend on the amount, density and atomic number of the inhomogeneity, as well as on the quality of the photon beam. Good agreement between dose distribution from EGSnrc and Geant4 code system in inhomogeneity phantom was observed, with dose differences around 5% and 7% for depth doses and dose profiles.