Evaluation of Geant4 to describe proton transportation for thick absorbers

Imaging techniques using protons are actively being developed currently to substitute X-ray computer tomography and nuclear magnetic resonance method in proton therapy. They deals with relatively thick targets like the human head or trunk where protons lose the major part of their energy, however they having enough energy to exit the target. The physical quantities important in proton imaging are proton exit energy, angle and coordinates. Nowadays many research groups are using The Geant4 toolkit for the development of proton imaging devices. However the most of available publications about validation of the Geant4 models are or for thin absorbers, or for energy deposition of completely absorbed protons (Bragg Peak), what are not important characteristics in proton imaging. The main objective of this work is to validate different models available on Geant4 (version 9.6.p03) taking into account its accuracy and computational performance from the viewpoint of proton imaging. This paper presents the comparison against experimental data published by Tschalär and Maccabee (for incident kinetic energies for protons of 19.68 MeV and 49.10 MeV). The results show that for the validation energies the spectra of the kinetic energy of the emerging protons: (i) there are differences between the validation and the different processes invoked for transportation and (ii) the validation energies are sensitive to sub-shell processes.