Some Relations between Cell Survival Models Having Different Inactivation Mechanisms

We consider two different types of cell survival models. In each model we assume that both irreversible and reversible lesions (or prelesions) can be formed by the radiation products from one energy-loss event. In the first model further energy-loss events can produce radiation products which can convert the reversible lesions to irreversible ones. The presence of even one irreversible lesion in the cell leads to reproductive death. In the second model reversible lesions can "react" by way of second-order kinetics to become irreversible and, as in the first model, the presence of one or more irreversible lesions leads to reproductive death. If the parameters in either model are chosen to have magnitudes which are required in the fitting of cell-survival data, approximate analytical survival probabilities can be found, and these are equivalent to the corresponding prediction of the Roesch model. At all stages of our mathematics we make approximations which are appropriate to low LET radiation.