The survival of aerobic and anoxic human glioma and melanoma cells after irradiation at ultrahigh and clinical dose rates.

This in vitro study was undertaken to determine if ultrahigh dose rates could improve the radiation response of human tumors. Two cell lines, human glioma (U-87 MG), which is radioresistant, and human melanoma (HT-144), which is radiosensitive, were irradiated at ultrahigh and high dose rates under aerobic and anoxic conditions to determine if their oxygen enhancement ratios are modified by dose rate. In fact, the survival curves, and hence the oxygen enhancement ratios, were found to be independent of the dose rate. The oxygen enhancement ratio for glioma cells irradiated in plateau phase was 2.8 (+/- 0.3). The oxygen enhancement ratio was 2.7 (+/- 0.4) for melanoma cells in plateau phase and 2.8 (+/- 0.3) in exponential phase. These results indicate that there is no advantage in treating these tumors using ultrahigh dose rates instead of conventional dose rates.