Recovery from radiation damage in human squamous carcinoma of the cervix.

The radiobiology of human carcinoma of the cervix has been investigated using five recently established cell lines. By means of an in vitro clonogenic assay, cell survival has been determined at dose-rates of 150, 3.2 and 1.6 cGy/min, and, in addition, split-dose experiments have been performed. Using approximately isoeffective doses (1 per cent cell survival), the amount of recovery observed using dose-rate and split-dose experiments has been correlated with the surviving fraction at 2 Gy (SF2 value) and the parameter alpha from the acute cell survival curves for the five lines. Two lines were radiosensitive, possessing significantly lower SF2 values (p = 0.03), and, at these isoeffect doses, showed significantly less sparing at low dose-rate (p = 0.012) and less split-dose recovery (p = 0.0096) than the three remaining cell lines. In general, the results indicate a good correlation between split-dose recovery-ratio, dose sparing achieved at low dose-rate compared to high, and SF2 value, and an inverse correlation with the alpha value derived from fitting dose rate dependence data to the incomplete-repair model of Thames. These observed differences in radiosensitivity within one human tumour type indicate the possible value of predictive testing of intrinsic radiosensitivity in the radiotherapy of carcinoma of the cervix.