A comparison of deep regional hyperthermia from an annular array and a concentric coil in the same patients

Twenty-two patients with advanced pelvic or abdominal malignancy (or both) were treated on successive occasions with hyperthermia produced by an annular array (AA) (60-80 MHz, 500-1800 W forward power) and a concentric coil (CC) (13.56 MHz, 350-1000 W forward power). Both devices were compared with respect to acute toxicity and power limitations. There was no power limiting factor in pelvic heating in 7/14 patients treated with the AA, however 13/14 experienced power limiting sacrococcygeal pain with the CC. The 9 patients who underwent abdominal heating had a variety of power limitations with both devices. Thermal mapping was performed in 23 treatments with the AA and in 19 with the CC. Composite thermal maps of patients with similar thermometry sites show that heating patterns produced by the CC were predictable from theory and static phantom measurements. The AA achieved broader regional heating, particularly at depth, but heating patterns were less predictable. Spatial thermal dose (TD) analysis revealed higher minimum tumor TDs and more favorable mean tumor/normal tissue TD ratios with the AA than with the CC. We conclude that the AA is superior to the CC for pelvic treatment and that both devices have limitations in abdominal treatment.