Geant4 electromagnetic physics model assessment for RBE-weighted dose calculation of carbon-ion radiotherapy

Abstract

Carbon-ion radiotherapy (CIRT) is being increasingly practiced owing to its advantages over conventional photon-based radiotherapy. Several CIRT-related dose calculation studies considering the biological effects of carbon ions were performed using the Geant4 Monte Carlo toolkit. For accurate RBE-weighted dose calculation in CIRT, the Geant4 physics models used in a simulation code need to be validated. Previous studies have validated the hadronic physics model of Geant4, but a validation study for electromagnetic (EM) physics models is missing. Therefore, we validated the Geant4 EM physics models for carbon RBE-weighted dose calculation. For the validation process in Geant4, the geometry used in the Microdosimetric kinetic model was irradiated by mono-energy beams between 0.1 and 1000 MeV/u of six elements (H, He, Li, Be, B, and C). The imparted dose calculated using various EM physics models is compared with the theoretical value. A G4EMStandardPhysics-based model is confirmed to result in breaking points for RBE-weighted dose calculations, whereas no such breaking points are observed when using our physics model and Geant4–DNA physics model. Because the breaking points observed in the results may induce uncorrected dose calculations, validating the EM physics models is recommended when performing carbon RBE-weighted dose calculation using Geant4.