Four human cell lines, one normal fibroblast and three tumour lines of differing radiosensitivities were evaluated for recovery from radiation damage, and for inhibition of this recovery by hyperthermia. The normal fibroblast, the glioma and the resistant ovarian carcinoma had about the same radiation resistance and sublethal damage recovery (SLDR) capacity. The sensitive ovarian carcinoma cell line had a much lower SLDR capacity. The potentially lethal damage repair (PLDR) capacity was greatest in the fibroblast and least in the resistant ovarian carcinoma. Hyperthermia for 30 min at 43 degrees C resulted in inhibition of SLDR and PLDR in all cell lines. Heating immediately after irradiation was most effective. In general, SLDR inhibition was greatest in the cell lines with the highest SLDR capacity while there was no such correlation with PLDR. Hyperthermia was most effective in the four cell lines tested when given immediately after the first dose of radiation of the split dose regimen. Thus, for clinical fractionated treatment, it may be most efficacious to give hyperthermia immediately after irradiation.

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