Therapeutic dose simulation of a 6 MV Varian Linac photon beam using GEANT4

A developed program in C++ language using GEANT4 libraries was used to simulate the gantry of a 6 MV high energy photon linear accelerator (Linac). The head of a clinical linear accelerator based on the manufacturer's detailed information is simulated. More than 2× 10⁹ primary electrons are used to create the phase space file. Evaluation of the percentage depth dose (PDD) and flatness symmetry (lateral dose profiles) in water phantom were performed. Comparisons between experimental and simulated data were carried out for three field sizes; 5 × 5, 10 × 10 and 15 × 15 cm². A relatively good agreement appeared between computed and measured PDD. Electron contamination and spatial distribution for both photons and electrons in the simulated beam are evaluated. Moreover, the obtained lateral dose profiles at 15, 50, and 100 mm depth are compatible with the measured values. The obtained results concluded that, GEANT4 code is a promising applicable Monte Carlo program in radiotherapy applications.