Role of Bcl-2 overexpression and nontargeted effect in the estimate of RBE-weighted doses for heavy ion therapy and BNCT

Sato, Tatsuhiko   ; Hamada, Nobuyuki*; Kumada, Hiroaki*

The planning of heavy ion therapy and BNCT requires radiation dose assessment with consideration of RBE for different radiation quality. We developed a model assembly for estimating the surviving fraction of cells irradiated with various types of ionizing radiation, considering Bcl-2 overexpression and nontargeted effects in the same framework. Using the model assembly in combination with PHITS, the RBE-weighted doses were estimated for several irradiation conditions in carbon-ion therapy and BNCT, the boron concentration and the Bcl-2 overexpression status in each cell being taken into account. The simulation suggested that the consideration of radioresistance due to Bcl-2 overexpression results in the significant increase of the RBE-weighted doses in tumor regions. On the other hand, consideration of nontargeted effects gives trivial impact on the RBE-weighted doses in tumor regions, but slightly increases the values in normal tissue regions.