An experimental study on the alteration of thermal enhancement ratio by combination of split dose hyperthermia irradiation

ABSTRACT

The study was undertaken to evaluate the alteration of thermal enhancement ratio as a function of timeintervals between two split dose hyperthermias followed by irradiation. For the experiments, 330 mice were dividedinto 3 groups; the first, 72 mice were used to evaluate the heat reaction by single dose hyperthermia and heatresistance by split dose hyperthermia, the second, 36 mice were used to evaluate the radiation reaction byirradiation only, and the third, 222 mice were used for TER observation by comibination of single dosehyperthermia and irradiation , and TER alteration by combination of split dose hyperthermia and irradiation. Foreach group the skin reaction score of mouse tail was used for observation and evaluation of the results of heatand irradiation. The results obtained are summarized as follows; 1. The heating time resulting 50% necrosis(ND 50)was 101 minutes in 43degrees centigrade and 24 minutes in 45degrees centigrade hyperthermia, which indicated thatthere is reciprocal proportion between temperature and heating time. 2. Development of heat resistance wasobserved by split dose hyperthermia. 3. The degree of skin reaction by irradiation only was increasedporportionally as a function of radiation dose, and calculated radiation dose corresponding to skin score 1.5(D1.5) was 4,137 rads. 4. Obtained thermal enhancement ratio by combination of single dose hyperthermia andirradiation was increased proportionally as a function of heating time. 5. Thermal enhancement ratio was decreasedby combination of split dose hyperthermia and irradiation , which was less intense and lasted longer thandevelopment of heat resistance. In summary, these studies indicate that the alteration of thermal enhancementratio has influence on heat resistance by split dose hyperthermia and irradiation.