Comparative study of alternative Geant4 hadronic

27 The distribution of fragmentation products predicted by Monte Carlo simulations 28 of heavy ion therapy depend on the hadronic physics model chosen in the simulation. 29 This work aims to evaluate three alternative hadronic inelastic fragmentation physics 30 options available in the Geant4 Monte Carlo radiation physics simulation framework 31 to determine which model most accurately predicts the production of positron32 emitting fragmentation products observable using in-beam PET imaging. Fragment 33 distributions obtained with the BIC, QMD, and INCL++ physics models in Geant4 34 version 10.2.p03 are compared to experimental data obtained at the HIMAC heavy-ion 35 treatment facility at NIRS in Chiba, Japan. For both simulations and experiments, 36 monoenergetic beams are applied to three different block phantoms composed of 37 gelatin, poly(methyl methacrylate) and polyethylene. The yields of the positron38 emitting nuclei C, C and O obtained from simulations conducted with each 39 model are compared to the experimental yields estimated by fitting a multi-exponential 40 radioactive decay model to dynamic PET images using the normalised mean square 41 error metric in the entrance, build up / Bragg peak and tail regions. Significant 42 differences in positron-emitting fragment yield are observed among the three physics 43 models with the best overall fit to experimental C and O beam measurements 44 obtained with the BIC physics model. 45