Dosage-Mortality in Rats Given Total Body Roentgen Irradiation. ∗

Summary

The LD₅₀ for total body X-radiation in Wistar rats is 640 ± 5 r with a 30-day endpoint. The time elapsing before 50%percnt; mortality occurs at different doses is a more reliable measure of mortality than the dosage-mortality curve or the dosage-survival time curves for different X-ray doses. The dosage-mortality curve of rats has such a steep slope in the LD₅₀ range that variations in mortality of from O to nearly 100%percnt; may occur in this range because of variations in animals and in the X-ray machine output. Therefore in studies directed toward (therapy or protection of animals given total body ionizing radiation, if the mortality curves are extremely steep as in the rat, dosages in the LD₅₀ range should not be used. Other measures which might be employed are discussed.