Hyperthermia can enhance the radiation effect as a synergistic reaction in irradiation combined with hyperthermia. Hyperthermia sensitize radioresistant S-phase and inhibit cellular recovery from the sublethal damage.

Ninety guinea pigs were divided into 4 groups for the experiment of application of irradiation combined with hyperthermia on their heart; (1) normal control group. (2) group receiving only hperthermia. (3) group receiving a single dose of irradiation of 10, 20 and 30 Gy resepectively. (4) group receiving varying single dose of irradiation like group (3) irradiation combined hyperthermia. Heating by 100 watt. 2450 MHz microwave hyperthermia on the heart was applied for 30 minutes maintaining 42~45℃ immediately following irradiation.

Microscopic examination and calculation of thermal enhancement ratio were carried out and results were as follows:

1) Hyperthermia alone did not evoke much changes. compared to normal control group.

2) In the group of irradiation alone. myocrdial muscle degeneration was noted in l0Gy irradiation and its severity was increased along with radiation dose.

3) In the group of irradiation alone. myocardial muscle necrosis was noted at 15 days after 20Gy irradiation. In the group of irradiation cmbined with hyperthermia. myocardial muscle necrosis was noted in l0Gy irradiation.

4) In the group of irradiation alone, interstitial fibrosis was noted at 15 days after 30Gy irradiation. In the group of irradiation combined with hyperthermia. interstitial fibrosis was noted at 15 days after 20Gy irradiation and its severity was increased along with radiation dose.

5) The thermal enhancement ratio(TER) was 1.5 on the end point of interstitial fibrosis of the guinea pig heart.