Validation of Monte-Carlo Geant4 code for Saturne 43 LINAC

The aim of this study was to model the 12 MV photon beam from a Saturne 43 LINAC configuring a 10×10 cm2 radiation field, this by finding the required adjustments to the electron source parameters namely the spot size, shape and energy distribution. The MC simulation tool Geant4 version 4.9.4 was used with rocks clustering software and Geant4 MPI Interface to parallelize our Geant4-based application. In this work, we have developed a user code for Saturne 43 LINAC simulation. This code has the capabilities to run multiple simulations at the same time, perform our own variance reduction techniques, writing and reading phase-space data using IAEA routines, and calculate dose distributions in a water phantom. In aim to speed up the treatment head simulation, we have developed two variance reduction techniques; the first one is based on stacking mechanism and called GAMMATEC, where the second one is a particular implementation of bremsstrahlung splitting and called BREMSPE. The combination of these two techniques can reduce required CPU time about five times. After optimization it was found that the appropriate mean energy, sigma and its full width at half maximum are 11.5 MeV, 0.4 MeV and 1.177 mm.