Dose rate dependence of response of mouse lung to irradiation.

The dose-rate dependence of lung damage in mice has been studied using LD50/50-180 as an index of the incidence of radiation pneumonitis. Mean lethal doses for 60Co gamma radiation to the thorax delivered at 100, 25 and 6 cGy/min were 1403, 1923 and 2488 cGy respectively. There were statistically significant differences between values obtained at 6 and 25 cGy/min and between those obtained at 25 and 100 cGy/min. An isoeffect plot of this data on a log-log graph shows the sparing effect of dose rate reduction to be greater for the lung than for more rapidly responding systems (colony forming units of small intestine and Chinese hamster cells in culture).