Extreme Hypoxia; its Effect on the Survival of Mammalian Cells Irradiated at High and Low Dose-rates

HeLa cells cultured in vitro have been used to measure the oxygen enhancement ratio for acute (110 rads/minute) and protracted (32 rads/hour) exposures to γ radiation. Values of 2·4 and 1·5 respectively were found to apply. It was also discovered that if cells are stored for 24 hours under conditions of extreme hypoxia their sensitivity to acute doses is increased; the survival curve loses its initial shoulder and becomes a simple exponential function of dose.