Bone marrow equivalent prompt dose from two common fallout scenarios.

A cell-kinetics model for radiation-induced myelopoiesis has been derived for mice, rats, dogs, sheep, swine, and burros. The model was extended to humans after extensive comparisons with molecular and cellular data from biological experiments and an assortment of predictive/validation tests on animal mortality, cell survival, and cellular repopulation following irradiations. One advantage of the model is that any complex pattern of protracted irradiation can be equated to its equivalent prompt dose. Severity of biological response depends upon target-organ dose, dose rate, and dose fractionation. Epidemiological and animal data are best suited for exposures given in brief periods of time. To use those data to assess risk from protracted human exposures, it is obligatory to model molecular repair and compensatory proliferation in terms of prompt dose. Although the model is somewhat complex both mathematically and biologically, this note describes simple numerical approximations for two common exposure scenarios. Both approximations are easily evaluated on a simple pocket calculator by a health physicist or emergency management officer.