Objective: This study investigated the changes in temperature of human muscle during microwave hyperthermia.
Methods: Skin surface and muscle temperatures were measured in 11 healthy adult males (age 24.3±2.2 yrs; height 174.2±6.1 cm; weight 70.0±5.3 kg) during a 30 min exposure of the thigh to 434-MHz microwave hyperthermia. The skin temperature was maintained at the pilot temperature of 40°C, and the temperature of the water in the bolus was 38°C. The peak power output was set at 60 W and controlled automatically to maintain the pilot temperature. Muscle temperature was measured in the vastus lateralis muscle at an average muscle depth of 2.0±0.2 cm using a 23-G Teflon-shielded thermocouple. Biopsy specimens were obtained for light microscopy from three subjects. A muscle equivalent phantom was used to evaluate the vertical heating pattern.
Results: Both of the skin and muscle temperature increased from baseline, and the muscle temperature was higher than the skin temperature (skin 39.2±0.5°C; temperature rise: 5.0±1.5°C, muscle 43.7±0.8°C; temperature rise: 8.9±1.4°C). At the end of the hyperthermia treatment, the muscle temperature decreased to 39.8±0.9°C, but it was still 4.8±1.5°C higher than baseline. No signs of muscle damage were observed based on blood creatine kinase activity and histological sections.
Conclusions: Our results show that the 434-MHz microwave hyperthermia treatment increased and maintained the muscle temperature locally by 6.3–11.4°C without muscle damage. These findings suggest that the microwave hyperthermia system provides effective and safe treatment.
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