Preliminary experimental investigation of radio frequency heating of spine and spinal cord and of heat tolerance of spinal cord

This is a preliminary experimental study on clinical application of hyperthermia with RF capacitive heating to the malignant neoplasms of spine and spinal cord. Canine lumbar or thoracic spine was heated with 13.9 MHz RF wave by placing electrodes dorso-ventrally. Temperature distribution in and around the spine was measured. Changes in spinal cord were studied with spinal cord evoked potential and histologically after the temperature of spinal cord was kept at 43-47℃ for 30 minutes, which lead to the following conclusions. 1. The dorso-ventral thickness of the canine used in this experiment was 13 to 15cm. Temperature in and around the spine was elevated up to 42～43℃ with RF electrodes of 20cm in diameter. With those of 10cm or 15cm, only back muscles were excessively heated. 2. Temperature monitoring in and outside spinal cord during RF heating revealed that the temperature within spinal cord was between that of dorsal and ventral epidural space. 3. Spinal cord evoked potential showed shortening of latency by heating below 44℃. Decrease of amplitude was added when heated above 45℃. Amplitude did not fully recovered after heating above 46℃. Delay in latency was not observed throughout different grades of heating, against reports hitherto published. 4. Histological destruction of spinal cord was observed after heating above 45℃. 5. The highest tolerable temperature of spinal cord in adult canine was estimated about 44℃ in 30 minutes' heating with RF wave