Clinical Usefulness of Determining the Rate of Thermal Clearance within Heated Tumors

Between June 1987 and June 1988, 28 patients (28 tumors) withliver, retroperitoneal, intrapelvic, or superficial tumors weretreated with hyperthermia combined with radiotherapy and/orchemotherapy. Hyperthermia was administered once or twice aweek for 30-60 min per session, up to a total of 2–11sessions, with an 8-MHz RF capacitive heating device. Bloodflow in the tumors was evaluated from the rate of thermal clearance(TCR) using the bio-heat transfer equation. The TCR was measuredin the middle of the first heating session and at the end ofthe last heating session by turning off the output power ofthe heating device. For 9 patients, contrast-enhanced CT scanswere taken and CT numbers at the centers of tumors were measuredbefore and after the entire course of hyperthermia. Changesin TCR were closely related to average tumor center temperature,changes in CT number, and tumor response. When smaller and moresuperficial tumors were treated by hyperthermia combined withradiotherapy and/or chemotherapy that consisted of many heatingsessions and during which a high average tumor center temperaturewas achieved, a better tumor response was obtained. The betterthe tumor response, the higher the local control rate became.The cause-specific survival rate of patients who achieved goodtumor responses was higher than that of patients who showedpoor tumor responses. Changes in TCR and CT number in heatedtumors were useful and important indicators of tumor responseto hyperthermia.