Evidence suggesting that the dose-response relationship for radiation-induced transformation in vitro is due to the degree of initiation in individual cells.

Experiments have been performed to elucidate whether the dose-response relationship for radiation transformation is likely to be due to the fraction of cells altered by the radiation exposure or to the degree of initiation in individual cells. Radiation doses of 0.25, 1, 4, and 6 Gy were utilized in experiments involving approximately 1 or 300 surviving irradiated cells per dish as the initial cell densities. The yield of transformants was approximately the same for each dose of radiation whether 1 or 300 viable cells per dish was utilized as the initial cell density in these studies. A dose-response relationship could be observed for radiation-induced transformation when single irradiated cells were assayed for their ability to give rise to malignantly transformed cells, suggesting that radiation is capable of altering the degree of initiation in individual cells. These results suggest that the dose-response relationship for radiation-induced transformation is due to the degree of initiation in irradiated cells.