Lack of effect of thermotolerance on radiation response and thermal radiosensitization of murine bone marrow progenitors.

We studied X-ray response, thermal radiosensitization, and time sequencing between heat and radiation for nontolerant and thermotolerant murine bone marrow cells. Survival curves of colony-forming units of granulocyte-macrophages (CFU-GM) have a D0 value of 1.26 +/- 0.04 Gy when irradiated in vivo. Heating at 44 degrees C for 30 min immediately prior to X-ray yields a D0 value of 0.96 Gy, with a thermal enhancement ratio of 1.3. Similar D0 and thermal enhancement ratio values were seen for thermotolerant cells. In vitro experiments with CFU-GM gave similar results. Studies of the effect of time sequence on heat and radiation indicate that for CFU-GM, the interaction between the two modalities do not fully disappear when given within 180 min of each other. Colony-forming units of erythrocytes (CFU-E) irradiated in vivo shows a D0 value of 1.1 +/- 0.03 Gy for radiation alone. Heating at 44 degrees C for 25 min prior to irradiation gives a D0 value of 0.95 Gy (thermal enhancement ratio, 1.1). Again, there was no change in the D0 value of radiation alone or the combination of heat and radiation in thermotolerant CFU-E. Both radiation killing and thermal radiosensitization were the same for thermotolerant and nontolerant CFU-GM and CFU-E.