Responses of four cell lines to continuous gamma irradiation applied at a dose rate of 0.1 Gy/h

The effectiveness of continuous irradiation applied at an ''ultra'' low dose rate of 0.1 Gy.h-1 was assessed in four cell lines (R-1, RUC-2, CH(V79) and Tg). This in vitro study was initiated because of the clinical interest in treating tumours by implanting 125I seeds. The dose rates applied to human tumours with this technique are in the same order of magnitude as those in the experiments to be described here. The results indicate that the response of a cell population to irradiation applied at an ultra low dose rate depends on at least three parameters: cell cycle time, intrinsic radiosensitivity and dose rate. A relationship is presented enabling one to estimate the dose rate required to eliminate a cell population if the cell cycle time and initial slope of the survival curve are known. (Auth.)