The cooling effect of tubular liquid flow during radiofrequency heating: the "rind" survival hypothesis

The influence of flowing blood on temperatures reached in nearby tumor cells during localized radiofrequency (RF) hyperthermia may be critical for tumor cell survival. We have investigated the effect on the temperatures nearby of blood flowing in a vessel. Using 13.56 MHz capacitive RF, we heated gel phantoms containing a tube through which cooling solution could flow. Our results demonstrated a reduction in temperature of the order of 3 degrees C around the tube when coolant was flowing, and the cooling pattern correlated with theoretical mathematical predictions. Up to 564 joules per minute could be removed from the system. Our results suggest the improbability of uniform tumor cell killing by RF heating. A scheme for integrating the concepts of physical cell damage, biochemical cell damage and peripheral cell survival in a tumor nodule is presented.