Figure 1.

Variations in the percentage clonogenic survival of V79-4 cells after irradiation with various doses of cobalt-60 γ-rays. Doses were delivered over fixed times of 30 (▼), 60 (▲) or 120 (♦) min. By way of comparison, cells were also irradiated either acutely (6 Gy/min), where exposure times were short (<3 min) and where little or no repair took place over the period of exposure, or at 0.2 Gy/min where exposure times were long. The slope of a cell survival curve given at low dose-rate tended to be shallower than those where various doses are delivered in a fixed time period. All irradiations were carried out with the cells at 37^oC. Error bars indicate ± SEM.