Assessment of Monte Carlo Geant4 capabilities in prediction of photon beam dose distribution in a heterogeneous medium

The aim of this study is the assessment of the Geant4 capabilities in accurately modeling of dose distribution in a heterogeneous water phantom. In this purpose, a Geant4 user code has been designed and developed to enable an accurate modeling of cross beam profiles in a heterogeneous water phantom deposited by a 12 MV photon beam emitted by a Saturne 43 Linac head and configuring a 10 × 10 cm² radiation field. The calculated cross beam profiles at two distinct depths (22 cm and 25 cm), were compared to the ones obtained with MCNPX code. Our findings show that the shapes of dosimetric curves at two distinct depths calculated with Geant4 code and the ones obtained by MCNPX code are in a very good agreement. However, the Geant4 code seems painfully slow when calculating those dosimetric curves and its associated statistical uncertainties don't seem to reach 1% after two weeks of calculations. To deal with this issue, we suggest that a new variance reduction technique specially addressed for dose calculation in a heterogeneous medium must be developed by the Geant4 collaboration, in order to decrease the required computing time and to improve the statistical of calculations.