Derivation and application of equations describing the effects of fractionated protracted irradiation, based on multiple and incomplete repair processes. Part 2. Analysis of mouse lung data.

General equations for fractionated protracted irradiation have been applied to the analysis of mouse lung data derived from isoeffect protocols. The data were accrued from a spectrum of different protocols including different radiation qualities, interfraction times and dose-rates. This analysis, based upon two component repair rate processes, suggests that there are possibly two repair-rate processes involved in the repair of sublethal damage in the lung. The two repair half-lives were 0.32 and 1.92 h with a low dose-rate partitioning of 1:0.38 between the amount of lethal damage resulting from rapid and slow sublethal damage repair processes at low dose-rates. The analysis also indicates that there may be a dose-rate amplification of the amount of resultant lethal damage, deriving from sublethal damage, associated with the longer repair process. It is also shown that the alpha/beta ratio is probably independent of the radiation quality and that the ratios of multiple to single event damage for 240kVp X-rays and 60Co are almost identical. However, the absolute values of alpha and beta for 240 kVp X-rays may be greater than for 60Co.