Effect of Dose-rate and Fractionation of X-ray Dose on Acute Lethality in Mice

Summary

The difference in x-ray dosage needed to kill mice acutely when the exposure varied from 12 min to 6 hours and the dose-rate from 3 to 55 rads/min has been studied. The effect of giving the dose divided into 72 separate fractions has also been described.

The dose needed to kill depends almost wholly on the overall exposure time, i.e. for continuous radiation the actual exposure time, or for fractionated doses the time between the start of the first dose and the end of the last one The longer the duration of exposure, the larger the dose required, but changes in dose-rate and number of fractions appeared to be of no consequence.

Two different multiple-regression equations, expressed in terms of dose and time only, provide an equally effective description of the response. Possible mathematical models leading to each of these equations have been suggested. It seems clear, however, that experimental data of the kind reported here cannot provide critical tests of current ideas about the rate of recovery from radiation.