الفهرس 
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Abstract
ABSTRCT
GATE (Geant4 Application for Tomographic Emission) is a general purpose simulation platform for PET, SPECT and radiotherapy applications. Built on top of the Geant4 simulation toolkit, it provides multiple new features with the objective to ease use of Geant4 in the field of medical physics. Handling Gate is carried out by scripting via a command language instead of C++ coding. In this study, gantry of a 6 MV photon beam of medical linear accelerator (LINAC), based on the manufacturer’s detailed information was simulated using GATE/GEANT4. This simulation was performed by using more than 2x 109 primary electrons. The simulation process is divided into two main stages. The first stage is to run the code to simulate photons and electrons transport through the Linac head, and record the information of the simulated hits crossing a scoring plane above the secondary collimator in a phase space file (PhS). The second stage is to generate hits histories from a given phase space file, and calculate dose distributions in a phantom relative to reference depth 1.5 cm at the isocenter. Evaluation of percentage depth dose distribution (PDD) and flatness symmetry (lateral dose profiles) in water phantom were performed. Comparison between experimental data and simulated were carried out for three field sizes 5 × 5, 10 × 10 and 15 × 15 cm2. Results show good agreement between computed and measured PDD, Moreover the lateral dose profiles at 15, 50, and 100 mm depth are compatible with the measured values. Overall, GATE/GEANT4 code is a promising applicable Monte Carlo program in radiotherapy applications.