SINGLE DOSE RADIATION AND HYPERTHERMIA AND GROWTH OF THE RAT TAIL

Abstract The growth of the tail of the weanling rat was used to study the effect of heat (43°, 44° and 45°C) 2–3 minutes following single doses of radiation (500–1500 rad) on proliferating normal tissue. Significant stunting of tail length (6.6 and 10.7%) was observed after heat treatment with 43° and 44°C for 1 hour. Shorter exposures of 43° or 44°C had no significant effect. Stunting from radiation alone ranged from 6.2% at 500 rad to 40% at 2500 rad. At low doses of x-irradiation (500 or 1000 rad), the heat effect was additive; however, at 1500 rad combined with 43° for one hour or 44°C for one half hour, the heat treatment potentiated the radiation effect. A comparison of the radiation alone, versus the combined treatment curves suggests that this potentiation may result from an increased effect on an hypoxic cell fraction in the normal tissue. The rule that a 1°C decrease in temperature is compensated by a heat duration factor of two to produce a given biological effect applied for heat alone, but not for heat following high dose radiation. Overall thermal enhancement ratios (TER) ranged from 1.05 to 1.34 depending on the individual treatments. At doses of 500 and 1000 rad, the TER's were largest when combined with 43° or 44°C for 1 hour, but when the heat effect was subtracted the resultant TER's were not significantly different from a value of 1.0.