Thermal distribution of magnetic-loop induction hyperthermia in phantoms and animals: effect of the living state and velocity of heating.

Hyperthermia has shown promise for the treatment of cancer. The magnetrode radio-frequency magnetic-loop induction applicator was recently introduced and is being evaluated at many centers with encouraging initial results. This investigation was undertaken to delineate the thermal distribution patterns of magnetrode hyperthermia in both normal tissue phantoms and healthy dogs. Temperatures on homogeneous and heterogeneous tissue equivalents and animal tissue phantoms, a dead animal extremity, a dead dog and a live dog subjected to rapid high-dose heating showed preferential and potentially injurious peripheral heating with a central "cold spot." However, sequential moderate-dose heating in live dogs showed virtually uniform (less than 1 degree C) and potentially tumoricidal temperatures greater than or equal to 42 degrees C in both peripheral and central internal organs without injury to surface tissues. These data indicate that magnetic-loop induction can produce potentially safe and effective deep central heat in living, normal animals, but that safety and effectiveness are significantly influenced by the velocity of heat deposition. Furthermore, normal tissue phantom models and dead animals are unreliable predictors of magnetrode heat patterns in living systems.