Use of combined systemic hypothermia and local heat treatment to enhance temperature differences between tumor and normal tissues.

The feasibility of combining local heat treatment with whole-body hypothermia in an effort to improve therapeutic gain was assessed. Superficial, nonperfused phantom tumors were fashioned in eight anesthetized mongrel dogs by transplantation of the spleen from the abdomen to a subcutaneous site on the hindlimb. After pretreatment of the animal with the vasodilator hydralazine (0.5 mg/kg, IV) to enhance normal tissue perfusion, the spleen implant was heated with a 2450-MHz microwave diathermy apparatus, first with the animal's core body temperature in the normal range (39 degrees C) and then after the animal had been packed in ice to reduce core temperature to 30 degrees C. Applied power density and temperatures in both the phantom tumor and underlying muscle tissue were recorded during brief interruptions of diathermy until steady-state temperatures had been achieved. Under normothermic conditions with time-averaged applied power of 0.038 W/ml to phantom tumor and 0.014 W/ml to underlying muscle, tumor temperature rose to 45.9 +/- 1.8 degree C, while muscle temperature remained at 40.5 +/- 0.7 degree C. During whole-body hypothermia applied power could be increased to 0.114 W/ml in phantom tumor and to 0.025 W/ml in muscle. Muscle temperature rose only to 33.8 +/- 1.6 degree C, while that of the nonperfused phantom tumor rose to 53.6 +/- 4.3 degrees C with systemic hypothermia.(ABSTRACT TRUNCATED AT 250 WORDS)