Development of a 70 MHz unit for hyperthermia treatment of deep-seated breast tumors

Hyperthermia of tumors in intact breast extending beyond the heating depth of our superficial 434 MHz CFMA antennas requires an alternative approach. A dedicated system was designed for this purpose, consisting of a treatment bed fitted with a 50×40×16 cm temperature controlled open water bolus. The patient lies in prone position with the breast immersed in the water positioned in front of a 34×20 cm 70 MHz waveguide placed in the bottom of the bolus. Hyperthermia was applied once a week for the whole breast with the 70 MHz applicator for 6 patients treated with thermoradiotherapy for deep lesions of recurrent breast cancer or melanoma. Two 14-sensor thermocouple thermometry probes were placed in catheters to monitor the invasive temperature. Results: The combination of 300-900 W antenna power and a water temperature of 42°C was well tolerated for the entire session of one hour and resulted in good tumor temperatures with T10 = 42.2°C, T50 = 41.1°C, T90 = 39.8°C. No toxicity or complaints were associated with the heating. A water mattress and other measures were needed to assure a comfortable position throughout the treatment. Conclusion: the 70 MHz breast applicator system performed well and tumor temperatures were good.