A comparison of thermal enhancement ratios for fast neutron and x irradiation of two normal tissues in rodents.

The effects of a hyperthermal treatment of one hour on radiation damage to baby rat cartilage and mouse intestine were compared for 250 kVp X irradiation and cyclotron-produced neutron irradiation (mean energy of about 7.5 MeV). Heat, in the range 41.0 degrees C-43.0 degrees C, caused no observable gross tissue injury when given alone. When heat was given immediately before radiation, the radiation damage was enhanced. There was no qualitative differences between response after fast neutrons and after X rays. Thermal enhancement ratios (TER) were similar for the two tissues and were not affected by the type of radiation used. Thus, the relative biological effectiveness (RBE) of fast neutrons compared with X rays was not markedly altered by combining radiation with hyperthermia.