Clinical experience with thermotron RF-8 capacitive heating for bulky tumors: University of Minnesota experience.

We conducted a phase I clinical trial of the feasibility of using the Thermotron RF-8, a capacitative heating device utilizing 8-MHz RF, for the treatment of deep-seated and bulky human tumors. Preclinical studies with agar phantoms demonstrated that deep heating can be achieved with this device when the electrode diameters are sufficiently large relative to the thickness of the heated object. In the clinical application of capacitive heating with radiofrequency, excessive heating of subcutaneous tissue has often been a problem. However, this could be minimized by continuous cooling of the subcutaneous fat with a 10 degrees C saline bolus, beginning more than 20 minutes prior to the start of heating. It was often possible to raise the temperature of deep-seated tumors even in obese patients by applying this pre-cooling method. The mean achieved temperature during 30 to 40 minutes of heating was higher than 42 degrees C and 40 degrees C to 42 degrees C in 26% and 50% of 58 tumors treated, respectively. A combination of hyperthermia (four to ten sessions, twice a week) with full-course or a limited dose of radiotherapy resulted in complete tumor remission in 7% of patients, and partial tumor remission in 50% of patients. In the full-course radiotherapy group, 69% of the tumors were judged to show complete or partial regression, and in the low-dose group, 43% of the tumors regressed completely or partially. Histologic examination of many of the tumors that did not regress showed massive necrosis, indicating that tumor size after hyperthermia is not an accurate criterion of the treatment result. Side effects were minimal, and vital sign changes during heating were insignificant. Our data, together with those reported by Japanese investigators, clearly demonstrated that hyperthermia with the Thermotron RF-8 in combination with radiotherapy is useful in treating deep-seated and bulky tumors that fail to respond to conventional treatment modalities.