Radiosensitivity and relative biological effectiveness based on a generalized target model.

By considering both cellular repair effects and indirect effects of radiation, we have generalized the traditional target model, and made it have a linear-quadratic-linear characteristic. To assess the repair capacity-dependent radiosensitivity and relative biological effectiveness (RBE), the generalized target model was used to fit the survival of human normal embryonic lung fibroblast MRC-5 cells in the G0 and G1 phases after various types of radiations. The fitting results indicate that the generalized target model works well in the dose ranges considered. The resulting calculations qualitatively show that the parameter ratio (a/V) in the model could represent the cellular repair capacity. In particular, the significant linear correlations between radiosensitivity/RBE and cellular repair capacity are observed for different slopes of the linear regression curves. These results show that the radiosensitivity and RBE depend on the cellular repair capacity and can be regulated by linear energy transfer. These analyses suggest that the ratio a/V in the generalized target model can also be used for radiation damage assessment in radiotherapy.