Regional Hyperthermia by Magnetic Induction in a Beagle Dog Model: Analysis of Thermal Dosimetry

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Abstract
Magnetic induction heating techniques for achieving normal tissue hyperthermia were investigated in a beagle dog model to clarify the physics and physiology of regional heating, to develop an animal model of regional heating in humans and to develop a method of rapid regional heating in dogs for a normal visceral tissue toxicity study. Heating was done with a concentric coil or a coaxial pair of coils applied to the abdominal region, and with or without surface cooling blankets in each case. Thermometers were placed at multiple visceral and s.c. sites including an intraarerial thermocouple at the aortic arch level. With either electrode arrangement and no surface cooling, whole-body hyperthermia (WBH) at 42.degree. C was produced within 30-55 min with 250 W applied power; the 42.degree. C state could be maintained with 40-60 W of power. Thermal gradients in these cases reflected nonuniform power depostion superimposed upon arterial temperature elevation. With surface cooling blankets added, systemic heating was significantly reduced, and temperature gradients again reflected the nonuniform power deposition. Regional heating in a dog produces WBH unless sifficient surface cooling is used to provide a heat dissipation rate balancing the heat absorption rate; this latter case best models the use of inductive techniques in humans. The coaxial pair of coils, without surface cooling, produced rapid WBH and the visceral temperature maximum and minimum were within Tesoph + 0.21.degree. C AND Tesoph - 0.0.degree. C, respectively (95% confidence index; Tesoph = esophageal temperature). This is an appropriate technique for the proposed toxicity study. [Implication of this work for cancer therapy are discussed.].