Aspects of radiation exposure that relate to epidemiological questions generally focus upon late effects due to low doses delivered at low dose rates. Among the questions of major concern, oncogenesis, mutagenesis, and teratogenesis are of primary interest, but in each case cell killing must also be considered. At the cellular level, few data exist relative to the foregoing except for cell killing but, even in the latter instance, technical difficulties impose limitations on the generalizations that may be inferred. Using cell survival as a model, several formal dose-effect relationships are discussed, particularly in reference to the low-dose region of the survival curve, and a summary of available survival data is presented. Of particular interest is the biophysics underlying so-called "single-hit" inactivation. The theory of exponential (or linear) dose-effect dependencies is presented, from which the conclusion is reached that in single-hit killing, the level of damage expressed (i.e., the inactivation constant) may be modified by postirradiation cellular processes reflecting damage repair or enhanced damage expression.

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