Changes in muscle temperature induced by 434 MHz microwave hyperthermia.

Objective: To investigate the changes in temperature of human muscle during microwave hyperthermia.

Methods: Skin surface and muscle temperatures were measured in 11 healthy adult men (mean (SD) age 24.3 (2.2) years; 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. Skin temperature was maintained at the pilot temperature of 40 degrees C, and the temperature of the water in the bolus was 38 degrees C. The peak power output was set at 60 W and controlled automatically to maintain the pilot temperature. The 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 skin and muscle temperatures increased from baseline, and muscle temperature was higher than skin temperature (skin temperature 39.2 (0.5) degrees C, temperature rise 5.0 (1.5) degrees C; muscle temperature 43.7 (0.8) degrees C, temperature rise 8.9 (1.4) degrees C). At the end of the hyperthermia treatment, muscle temperature decreased to 39.8 (0.9) degrees C, but was still 4.8 (1.5) degrees C higher than the baseline. No signs of muscle damage were observed on the basis of the blood creatine kinase activity and histological sections.

Conclusions: The results show that the 434 MHz microwave hyperthermia treatment increased and maintained muscle temperature locally by 6.3-11.4 degrees C without muscle damage. These findings suggest that the microwave hyperthermia system provides effective and safe treatment.