Cell recovery kinetics for split-dose, multifractionated and continuous irradiation in the DSB model

The recovery kinetics for split-dose, multifractionated and continuous irradiations were considered in the framework of the DSB model (Ostashevsky 1989) with the assumption of a cooperative type of DSB repair. Two types of in vitro split-dose experiments can be distinguished on the basis of the time of cell plating: (i) IP, where cells are plated immediately after the second dose; and (ii) DP, where cells are incubated for a long period after the second dose before plating. The model predicts that the IP split-dose recovery kinetics depend mainly on the first dose and are not described by a single exponential curve. The rate of these recovery kinetics is faster than that of DSB repair. In contrast, the DP split-dose recovery kinetics are dose-independent and described by a single exponential curve, the time constant of which coincides with that for DSB repair. The equation for cell survival after multifractionated and continuous irradiations, derived in this work, are different from those in other models (e.g. incomplete repair (IR)) and represent an alternative which is worth testing. The values of the repair time constant estimated from these equations are at least 1.5-2-fold longer than those estimated from the IR equations applied to the same experimental data.