Modeling considerations for improving accuracy of a proton therapy beam with GEANT4

Simulations of a clinical proton treatment nozzle with GEANT4 were performed and compared against measured data to assess simulation accuracy. Various parameters were then adjusted to examine their effect of accuracy and determine optimal values. This analysis included GEANT version (9.3 and 9.5), range cuts, step max, and initial beam model. GEANT4 version 9.5 was found to give better range accuracy than version 9.3. Simulation accuracy was found to not be very sensitive to range cuts and step max parameters, but recommended values for high accuracy simulations are 250 11m for range cuts and 0.1 mm for step max. Finally, the initial beam model was shown to change the lateral profile in the phantom, however, lateral profiles still show significantly higher error rates than depth profiles.