Dose dependence of the oxygen enhancement ratio (OER) in radiation inactivation of Chinese hamster V79-171 cells.

The dose dependence of the oxygen enhancement ratio (OER) has been examined through multiple measurements of the response of Chinese hamster V79-171 cells to low and high doses of radiation under aerobic and hypoxic conditions. In this series of experiments the cells were maintained at 37 degrees C throughout the gassing and irradiation periods, to simulate normal physiological conditions. Flow cytometry and cell sorting techniques were used to facilitate accurate measurement of cell survival throughout the dose range, but particularly at low dose. The OER was found to decrease significantly at low dose, qualitatively confirming earlier reports from this laboratory, though the decrease was somewhat smaller in the present series. This difference may be a temperature effect since in the earlier experiments irradiation was at 0 degree C. This report shows that the OER decreases from a value of 2.87 +/- 0.16 (standard deviation of mean) at S = 0.01 to 2.36 +/- 0.19 at S = 0.80. Both alpha and beta are altered by the presence of oxygen. The OER is presented as a function of dose in nitrogen.