Radiosensitivity and Recovery from Radiation Damage in Cultured CHO Cells Exposed to Hyperthermia at 42.5 or 45.5°C

Abstract

The effect of hyperthermic treatments [an adjurant to the radiotherapy of cancer] (42.5 or 45.5.degree. C) on recovery from radiation damage was examined. Recovery from sublethal damage (SLD) when heat was administered prior to irradiation was not inhibited by small heat treatments (survival reduced to 80% by 30 min at 42.5.degree. C or 4 min at 45.5.degree. C) for either temperature, but recovery was inhibited by larger heat treatments (survival reduced to 10% by 120 min at 42.5.degree. C or 15 min at 45.5.degree. C). Thus, the effects of 42.5 or 45.5.degree. C on recovery from SLD were similar when the heat treatments resulting in equal survival levels were used. Recovery from potentially lethal damage (PLD), as measured by incubation at 20.degree. C after a combination of radiation and heat treatments was observed when a small heat treatment (30 min at 42.5.degree. C) was given either before or after irradiation. The amount of radiosensitization, i.e., the thermal enhancement ratio (TER), calculated at the survival level of 10-3, correlated with the amount of cell killing resulting from the heat exposure alone, irrespective of the temperature at which the cells were treated.