1978a: High LET Constraints of Low LET Survival. Phys

Survival curves for biological cells irradiated with gamma rays (and other low LET radi-ations) cannot be properly interpreted without examining the implications of these inter-pretations for high LET radiations. The theory of RBE demands that the RBE of any high LET radiation field is at most one when the probability for cell killing as a function of the absorbed dose of gamma rays is linear or sublinear, for homogeneous samples whose ra-diosensitivity parameters are not altered during the irradiation. A contrary experimental finding strongly suggests that the experimental sample is heterogeneous. Violation of this constraint is not unusual where the survival curve found with low LET radiations has a well defined initial negative slope. 1