Physics Settings for Using the Geant4 Toolkit in Proton Therapy

We simulated electromagnetic and nuclear processes induced by clinical proton beams in order to select the physics setting for the 8.1 version of the Geant4 toolkit. A modular physics list was constructed allowing for alternative processes and models to be invoked in the simulations. We validated the Monte Carlo by means of measured depth-dose distributions in water for 86 MeV and 209 MeV beams and measured longitudinal charge profiles in a stack of polyethylene absorbers (multilayer Faraday cup) for a 160 MeV beam. Best agreement between simulation and measurement was found for the standard electromagnetic and binary cascade models of Geant4.