Oxygen Sensitization of CHO Cells at Ultrahigh Dose Rates: Prelude to Oxygen Diffusion Studies

Abstract

The response of cultured CHO cells to ultrahigh dose rate (approx.10/sup 11/ rad/sec) radiation, as measured by colony-forming ability, was studied under various oxygen concentrations with single electron pulses of 3 nsec duration. A thin-layer technique was designed for these experiments to permit rapid equilibration of the cells with the ambient oxygen-containing gas and to ensure that no segments of the cell population were shielded from the relatively low energy electrons (average energy, approx.450 keV), thus eliminating the possibility of artifacts influencing surviving fraction. Dosimetry was performed using a combination of calorimetric, charge-measuring, and thermoluminescent techniques. At a concentration of 0.44% oxygen, breaking behavior of the survival curve was observed in accord with the radiolytic depletion of intracellular oxygen by the radiation pulse. The sensitivity for doses greater than the breakpoint dose followed an anoxic response, clearly different from that observed when the cells were irradiated at conventional dose rates in the same gas under the identical geometry. The breakpoint dose was found to be approximately linear over the oxygen concentration range 0 to 0.7%. These results are consistent with recent observations of mammalian cell response under high-intensity irradiation conditions and provide a basis for the design of a double-pulsemore » experiment.« less