Geant4 Simulation Study of Dose Distribution and Energy Straggling for Proton and Carbon Ion Beams in Water

Dose distribution and energy straggling for proton and carbon ion beams in water are investigated by using a hadrontherapy model based on the Geant4 toolkit. By gridding water phantom in NxNxN voxels along X, Y and Z axes, irradiation dose distribution in all the voxels is calculated. Results indicate that carbon ion beams have more advantages than proton beams. Proton beams have bigger width of the Bragg peak and broader lateral dose distribution than carbon ion beams for the same position of Bragg peaks. Carbon ion has a higher local ionization density and produces more secondary electrons than proton, so carbon ion beams can achieve a higher value of relative biological effectiveness.