Development of a microwave-induced hyperthermia system with multiple applicators.

A hyperthermia system which has been developed for clinical use is described. Five helical coil applicators operating at the microwave frequency of 2450 MHz were used for inducing hyperthermia in superficial tumors to the depth of approximately 5 cm in regions of extreme curvature (i.e. extremities, breasts, head and neck) by superimposing several beams from the multiple applicators. The microwave generators were controlled by a microcomputer governed by temperature measurements from thermocouple probes inserted into the tissue. This system was evaluated with respect to the local specific absorption rate (SAR) of the electromagnetic energy for two agar gel phantoms. The relationship of temperature versus depth in four patients was measured with 2-4 applicators (total, 250-600 Watt). Up to May, 1989, 70 patients with superficial tumors, esophageal cancer and carcinoma colli had been treated with radiotherapy combined and local hyperthermia using this system.