Design and Modeling of Medical Linear Accelerators Using the Geant4/GATE Platform

The aim of this research is to investigate the use of GATE, the Monte Carlo simulation application based on Geant4 toolkit to estimate the Percent Depth Dose (PDD) and Off-Axis Ratio (OAR) of a novel medical Linear Accelerator (Linac) for photon mode field sizes 5 × 5, 10 × 10, 20 × 20, 30 × 30 and 40 × 40 cm² and also for electron mode field sizes 5 × 5,10 × 10, 15 × 15 and 20 × 20 cm² at the isocenter. The simulations for the two modes were performed at two different initial electron beam energies; 6 MeV and 10 MeV. A model for the 60 × 50 × 40.75 cm 3 PTW MP3 water phantom was used in the simulations. Firstly, verification of the dose calculations of two medical linacs: Siemens ONCOR for field sizes 10 × 10, 20 × 20 and 30 × 30 cm² and Varian 600C for field sizes 3 × 3, 6 × 6 and 9.8 × 9.8 cm² using 6 MeV electron beam, were confirmed. According to this study, the PDD and OAR comparisons in terms of the gamma passing rates have shown satisfactory agreement between the measurements and the simulation results. For the novel medical linac, the PDDs and OARs were simulated for the photon and electron modes with two energies, 6 MeV and 10 MeV. All the results agreed with the general dose distributions of medical linear accelerators from common manufacturers. We predict there will be an agreement between the measurement and the simulation. The calculated dose distributions coupled with the flexibility of GATE in designing and modeling of medical linear accelerators are very promising. The GATE MC simulations could be considered as a very attractive tool for estimation of the radiation doses from any medical linac for both the photon and electron modes.