[Theories on radiobiological effects (author's transl)].

Radiobiology has revealed two entirely different effects on irradiated cells. An early, interphase, death (alpha-effect) and also sublethal and potential lethal damage causing mitotic abnormalities leading to a delayed death (beta-effect). The alpha-effect, caused by relative great ion densities, is now interpreted as a double break of the DNA molecule in the cell nucleus. The beta-effect, caused by smaller ion densities might be due to adjacent single breaks of the DNA. The nonlinear dose dependent of the beta-effect can be explained by rapid repair processe having a limited repair capacity. Slow repair of damaged normal cells in G1-phase can be enhanced by medical means and this might be important for clinical radiotherapy.