Test of the nuclear interaction model in SHIELD-HIT and comparison to energy distributions from GEANT4.

Monte Carlo codes are widely used to simulate dose distributions in ion radiotherapy. The benchmark of the implemented physical models against experimental data plays an important role in improving the accuracy of the simulations. To estimate the accuracy of the inelastic cross sections in SHIELD-HIT, the simulated charge is compared to measured data from a Multi Layer Faraday Cup. In addition, the results are compared to GEANT4, which are already published. Furthermore, energy distributions are simulated with SHIELD-HIT07 and GEANT4.8.1. From a comparison of depth distributions and beam profiles of 100 and 200 MeV protons, we estimate the level of agreement of the two codes. Nuclear interactions predicted by SHIELD-HIT underestimate the total amount of measured charge. The energy distributions from SHIELD-HIT and GEANT4 show differences exceeding the statistical uncertainties of 2%. Due to a difference of the Bragg curve of 0.5 +/- 0.3 mm on average, the mean difference in dose is 3.5% with a maximum deviation of 7% for the simulated cases.