Improved Preferential Tumor Hyperthermia with Regional Heating and Systemic Blood Cooling: A Balanced Heat Transfer Method

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Abstract
Absorption of power in large body volumes can occur with some approaches used for hyperthermia treatment of cancer. A systemic heat absorption rate exceeding the heat dissipation rate can lead to systemic temperature elevation that limits the magnitude and duration of application of power and hence the degree of preferential tumor temperature rise. A hyperthermia approach was described consisting of regional electromagnetic power absorption and extracorporeal blood cooling with regulation of both sytemic heat absorption and dissipation rates (balanced heat transfer). A test of this approach in 5 dogs with nonperfused tumor models demonstrated intratumoral temperatures > 42.degree. C, while systemic temperature remained at 33.degree. C and visceral temperatures within the heated region equilibrated between 33.degree. and 42.degree. C. Solutions of the bioheat transfer equation were obtained for a simplified model with a tumor perfusion rate lower than surrounding normal tissue perfusion rate. In this model, the use of arterial blood temperatures < 37.degree. C allowed higher power densities to be used, for given normal tissue temperatures, than when arterial temperature was .gtoreq. 37.degree. C. As a result, higher intratumoral temperatures were predicted. Control of arterial blood temperature using extracorporal cooling may thus limit systemic temperature rise produced by regional heating devices and offer a means of improving intratumoral temperature elevations.