Kinetics of cell survival as predicted by the repair/interaction model

A functional relationship determining the survival curve for reproductive cell death caused by low-LET radiation is derived on the basis of Lea's repair/interaction model. Radiation-induced primary lesions are assumed to interact pair-wise to form long-lived lethal lesions, simultaneously with the repair of the primary lesions. The formula derived for a short single irradiation gives a typical shouldered survival curve. At doses below the shoulder the interaction entirely occurs at low levels of primary lesion concentration, resulting in the parabolic shape of the logarithmic survival curve. At higher doses the interaction initially proceeds at high levels of primary lesion concentration, a state whose duration is determined by the dose and the finite speed of the first-order reaction of repair; this initial phase of the interaction results in the exponential tail of the survival curve. Survival after fractionated and protracted irradiation are also obtained. The dependence of cell survival on the irradiation conditions can be interpreted in terms of the basic parameters of the model.