The relative biological effectiveness of 100 kV X-rays determined by the V-79 cell colony assay.

The relative biological effectiveness (RBE) of 100 kV X-rays compared with cobalt-60-gamma-irradiation was determined using a cell colony assay based on the survival of Chinese hamster V-79 lung fibroblasts. The 37% dose (Do) was found to range from 1.12 to 1.47 and from 1.33 to 1.63 Gy for X-rays and 60Co-gamma-irradiation respectively. The mean RBE value calculated from the Do values was found to be 1.13 +/- 0.04. This figure compares favourably with RBE values calculated from Do values using other endpoints.