RBE of carbon ions: experimental data and the strategy of RBE calculation for treatment planning.

The main reason for the application of heavy ions like carbon in radiotherapy is the enhanced relative biological effectiveness RBE. In contrast to neutrons where RBE is widely independent from penetration depth, high energy carbon beams have a low RBE at the entrance and a high RBE in the target-volume. Therefore, the side effects to normal tissue are small, while the tumor response can be maximized. In the paper, experimental RBE values for inactivation are compiled, that demonstrate the RBE dependence from the repair capacity. In a theoretical approach, the local effect model (LEM), this dependence is used to calculate clinical RBE. Examples for clinical RBEs are given that have been applied to patient treatments.