Carbon therapy of brain tumors and the effect of phantom compositions on dose calculations using Monte Carlo simulations

Due to the unique properties of carbons in depth-dose deposition, this study investigated the carbon therapy of brain tumors using the Geant4 toolkit. To see the effect of phantom material on the dose calculations, three phantoms consisting of realistic brain tissue, soft tissue, and water were considered. The spherical tumor was considered at the center of the brain and the Bragg peak was calculated at the center of the tumor. The dose deposition in depth was different for all three phantoms, so that this difference is about 3 mm for the Bragg peak in the brain phantom and soft tissue phantom, and about 4 mm for the Bragg peak in the soft tissue and water. The depth dose distribution of the secondary particles indicates that the photons deposit most of their dose close to the surface, while for alpha and protons it depends on the Bragg peak depth. Also, the deposited dose in the tumor is more than one hundred times larger than the deposited dose in the brain healthy tissue, and ten thousand times higher than the organs such as the thymus gland and thyroid. The results of this investigation confirmed that more effort should be made to use more realistic phantoms in treatment design.