The effect of hyperthermia on the early and late appearing mouse foot reactions and on the radiation carcinogenesis: effect on the early and late appearing reactions.

The effect of hyperthermia on radiation-induced early- and late-appearing foot reactions was studied in C3Hf/Sed mice derived from our defined flora mouse colony. The animal foot was irradiated with 137Cs gamma-rays under hypoxic, air, or hyperbaric oxygen (O2 30 psi) conditions. Hyperthermia of 43.5 degrees C for 45 min was given locally in a water bath where a constant temperature +/- 0.1 degrees C was maintained. Treatment intervals between the 2 treatments were 20 min and 2 days. For the early-appearing reactions scores taken between the 14th and 35th post-irradiation days were averaged. Late-appearing reactions became apparent after approximately the 200th post-treatment day and increased with time. The foot reaction was enhanced by hyperthermia given 20 min before or after irradiation. Dose response curves for radiation given 20 min after hyperthermia for acute-appearing reactions lacked shoulders, whereas those following the same treatment schedule for late-appearing reactions showed significant shoulders. The thermal enhancement ratios (TER) for score 2.0 (complete epilation) early- and late-appearing reactions depended on the treatment interval and sequence. The TER values were greater for a short treatment interval (20 min.) than for a long treatment interval (2 days). Thermal enhancement was greater for hyperthermia given before irradiation compared to the reverse sequence. The TER values were always smaller for the late-appearing reactions than for the acute-appearing reactions. The relationships between early reaction scores and late reaction scores showed that the late reactions following combined heat and radiation are less extensive than those following radiation alone if they were compared at radiation doses which induced an equal level of early reactions. This difference was most significant at low early reaction scores and decreased with increasing score level.