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

• Published in: Radiation research 1978-12, Vol.76 (3), p.510-521
• Main Authors: Michaels, Howard B., Epp, Edward R., Ling, C. Clifton, Peterson, Eleanor C.
• Format: Article
• Language: English
• Subjects: Air; Animals; Cell lines; Cell Survival - drug effects; Cell Survival - radiation effects; Cells, Cultured; CHO cells; Cricetinae; Dose-Response Relationship, Radiation; Dosimetry; Electrons; Gamma Rays; HeLa cells; Hypoxia; Irradiation; Methods; Nitrogen; Oxygen; Pulsed radiation; Radiation dosage; Radiation, Ionizing; Radiation-Sensitizing Agents; Radiotherapy; X-Rays
• ISSN: 0033-7587; 1938-5404
• DOI: 10.2307/3574800

The response of cultured CHO cells to ultrahigh dose rate $(\sim 10^{11}\ {\rm rad}/{\rm sec})$ radiation, as measured by colony-forming ability, has been studied under various oxygen concentrations with single electron pulses of 3 nsec duration. A thin-layer technique has been 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, ∼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-pulse experiment.