Experimental Radiobiology of Ion Beams

In treatment planning, the increased effectiveness of ion beams is considered by the relative biological effectiveness (RBE). As the RBE depends on ion species, linear energy transfer (LET), dose as well as on various biological factors, it is calculated by biomathematical models. These models were initially developed based on in vitro data but need to be further validated in vivo. Our group performs systematic dose response studies at the Heidelberg Ion Beam Therapy Center (HIT) to determine preclinical RBE-values in normal tissues and tumors as a function of the most important physical and biological parameters. For preclinical normal tissue, the RBE is determined at different positions within a 6 cm spread-out Bragg peak (SOBP) using different dose levels and ion species. The results are used to benchmark predictions of clinically applied RBE-models. For preclinical tumors, the impact of hypoxia, tumor differentiation and tumor growth on local tumor control is determined. These experiments are supported by imaging studies to identify predictive parameters for normal tissue and tumor response. Further investigations on the histological and molecular level are performed to identify the mechanisms.