Responses of cultured mammalian cells to prolonged low dose rate gamma irradiation.

Experiments were performed to verify the finding of others that prolonged irradiation caused sudden death of cells. Continuous irradiation (dose rate 0.09 Gy/h) was applied to the R-1, RUC-2, V79 and T-1g cells for up to 140 days. End points were: population growth rate, plating efficiency and radiosensitivity. The population doubling times were increased and plating efficiencies decreased; cell survival after single doses at acute dose rate were lower than that of control cells. Part of the cell parameters returned to control values within three weeks after prolonged irradiation had been terminated. Sudden death after prolonged exposure was not observed.