The Inactivation of Chinese Hamster Cells by X Rays: The Effects of Chemical Modifiers on Single- and Double-Events

The radiation inactivation of the proliferative capacity of Chinese hamster fibroblasts is described by the linear--quadratic relationship, S/S$sub 0$ = exp (-$alpha$D - $beta$D$sup 2$). Values of $alpha$ and $beta$ have been determined for asynchronous cells irradiated under various conditions of chemical radioprotection and radiosensitization. OH has been found to contribute to cell inactivation by both $alpha$ (single-events) and $beta$ (double-events). Sulfhydryl repair was found to provide radioprotection against single- and double- events while molecular oxygen was found to radiosensitize predominantly by enhancing double-events. Electron-affinic radiosensitizers enhanced the double- event component. These radiation chemical effects on cell inactivation are discussed with reference to potential molecular targets and lesions and the microdosimetry of 250 kV X rays in water. (auth)