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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 50×40×16cm temperature controlled open water bolus. The patient lies in prone position with the breast immersed in the water positioned in front of a 34×20cm 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 300–900W 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.