Cellular radiosensitivity of a rat brain tumor.

The response of a model brain tumor system in the rat to single doses of x irradiation has been studied. Solid tumors were exposed in situ, removed, dissociated into single cells, and grown in tissue culture. The fraciton of surviving clonogenic cells wasdetermined as a function of x-ray dose level for tumors irradiated in anesthetized, air-breathing rats, and for tumors irradiated in rats killed 5 minutes prior to irradiation bynitrogen gas asphyxiation. The parameters of the survival curve for tumors irradiatedin air-breathing rats were: DO= 295 rads; DQ= 350 rads; and n= 3.0. Similarly, thesurvival parameters for tumors irradiated in nitrogen gas asphyxiated rats were: DO=625 rads; DQ=675 rads; and n= 3.0. The survival curve of these tumor cells when assayed in in vitro tissue culture only has parameters of: DO= 225 rads; DQ= 350 rads; andn= 4.7. Data form the in vivo to in vivo tumor cell survival curves suggest that there is no significant hypoxic fraction in this brain tumor.