Radiation Mortality in the Mouse: Model of the Kinetics of Injury Accumulation: II. Protracted Doses in the Supralethal Range

The eifect of exposure time on the extent of acute radiation injury was investigated in the LAF/sub 1/ mouse. Exposures to Co/sup 60/ gamma rays were protracted over single periods ranging from 80 min to 1 day. Doses were in the 30-day lethal range, and most deaths occurred in the 9- to 30-day period. The hematopoietic syndrome was the most prevalent lethal mechanism with which death in this period was associated. Dose eifecttveness depended on duration of exposure; there was a constant linear decrease in dose effectiveness with increase in exposure period through 6 hr, but there was relatively little further decrease when doses were protracted over longer periods. A kinematic model is presented that describes the dependence of lethality on length of protraction. The model assumes the independent action of two kinettcally different injury processes: a timedependent (reversible) process regulated by a linear reversal of radiation effects and expressed in groups exposed for periods of 360 min or less; and a timeindependent (irreversible) process predominately expressed as mortality in groups exposed for 960- or 1440min periods. By use of the model, sensitivity differences between various strains and species, as well as between different qualities of radiation, can be normalized.more » Data reported by several investigators were subjected to this transformation, and the constants of the relation between the transformed variable and exposure time are shown to be approximately the same. (auth)« less