Distributions dose analysis for 6 MV photon beams using Monte Carlo-GEANT4 simulation

Monte Carlo is a method that widely used for calculation of particle transport in radiotherapy dose distribution. This study was devoted to develop a linear accelerator head geometry model (LINAC) using GEANT4 simulation for 6 MeV photon beam. The geometric model of the accelerator head consists of electron sources, target, primary collimator, flattening filter, jaws, and MLC (multi-leaf collimator). The homogeneous water phantom size of 40 × 40 × 40 cm³ was used in the simulation, 100 cm SSD (source-skin distance), and field size are 5 cm × 5 cm, 10 cm × 10 cm, 20 cm × 20 cm, and 30 cm × 30 cm. The simulation results show the peak curve energy positions are in the range 0.3 MeV – 0.4 MeV and the maximum absorbed energy is about 5.9 MeV. According to the landau curve fitting the mean energy is about 0.385 MeV. The results of GEANT4 simulation show the energy spectrum has the same pattern as an energy spectrum from several experiments of LINAC head geometry. The simulation results also show the dose distribution based on beam profile and depth profile of water phantom with different fields.