Monte Carlo modeling of 6 MV and 18 MV photon energy spectra for radiotherapy using the GATE/GEANT4

Energy spectrum modeling is crucial in radiotherapy. In this paper, we present a Monte Carlo (MC) simulation-based approach to generate and model reliable energy spectra. We simulated the accelerator head for energies of 6 MV and 18 MV and validated our results by comparing them with experimental data. The phase spaces obtained during the simulation were used as a source to ensure their reliability. From these data, we generated energy spectra modeled by functions. The models obtained from the energy spectra are in the form of functions composed of several distinct polynomial equations, each describing a precise energy interval to ensure the correct reproduction of these spectra. This modeling allows providing predefined models for direct use of one of them by incrementing one of them according to the desired energy as a source during subsequent simulations in radiotherapy.