Possible dose rate dependence of recovery kinetics as deduced from a preliminary analysis of the effects of fractionated irradiations at varying dose rates.

Data relating to jejunal crypt survival following fractionated total body irradiation of C3H mice have been subjected to a preliminary analysis using the linear-quadratic formalism. Because the regimes considered involved fairly closely-spaced fractions, delivered at dose rates in the range 1.2-72 Gy h-1, it was necessary to further develop previously established forms of the model in order to carry out the evaluation. The magnitude of the recovery half-life has been deduced for each of the regimes and found to be in the approximate range 0.1-0.6 h. For any given fraction number, the half-life appears to be markedly dependent on dose rate, increasing with dose rate up to approximately 25 Gy h-1, falling off thereafter. Tentative reasons for this behaviour are given, together with an assessment of the possible shortcomings of the analytical method.