Theoretical feasibility of vasodilator-enhanced local tumor heating

Normal arterioles, in contrast to the abnormal microvasculature of many solid tumors, provide a target for selective drug action which can enhance local heat treatment of the tumors. Measurements of tissue blood flow with radioactive microspheres and estimates of changes in blood flow with thermal clearance methods revealed that vasodilator drugs either decreased or did not alter blood flow in hamster melanoma, rat hepatoma and canine transmissible venereal tumor while increasing perfusion in adjacent normal tissues 2 to 4-fold. Solutions of the bio-heat transfer equation, which take into account such selective effects of vasodilators on blood flow in normal tissues, clearly demonstrate improved selective heating for spheroidal tumors over 2 cm in diameter. In the presence of vasodilator drug effect, steady-state center tumor temperatures of 45-50 degrees C can be achieved by increased power input, while surrounding normal tissues remain below 42 degrees C.