Split-dose recovery explained quantitatively by repair of potentially lethal lesions.

It is known from experimental and theoretical considerations that the shoulder in the usual dose-survival curve for mammalian cells is due to repair of potentially lethal lesions (PLL). As a consequence, reappearance of the shoulder in a split-dose experiment should also be related to repair of PLL. A procedure for calculation of cell survival curves for split-dose irradiation is described which takes into consideration repair of PLL only. The reproduction of the shoulder with increasing time interval between the two dose fractions can be seen to take place with a time constant closely related to that of repair of PLL. Other quantitative parameters such as the dose dependence of this recovery time constant can be predicted quantitatively from the calculation.