Hyperthermia of deep seated pelvic tumors with a phased array of eight versus four 70 MHz waveguides

Hyperthermia, increasing tumor temperatures to 40–43°C for 1 h, enhances the effectiveness of radiotherapy and chemotherapy. Deep seated pelvic tumors are usually heated by arrays of radiofrequency or microwave antennas placed around the patient. During hyperthermia treatment-limiting hot spots may arise in normal tissue. The AMC-8 device with eight 70 MHz waveguides was designed to overcome this issue by improving power steering abilities compared to the four waveguide AMC-4 device. Four patients with pelvic malignancies were treated with this system. Each patient received 2–3 treatments using 4 waveguides and two treatments using 8 waveguides, all at a total power of 550W. Average steady state tumor temperatures T90 and T50 were 39.9°C and 41.3°C for 4 waveguides and 39.7°C and 41.4°C for 8 waveguides, respectively. Toxicity was minimal with a lower incidence of hot-spots for eight waveguides. The transition from 4 to 8 waveguides was associated with unchanged tumor temperatures and a reduction in hot spots. Thus higher power levels and higher tumor temperatures can be achieved with the 8 waveguide configuration.