Hyperthermia induction with thermally self-regulated ferromagnetic implants.

We have developed a self-regulating thermoseed for interstitial hyperthermia treatment of tumors. The seeds are made of a 70.4% nickel-29.6% copper alloy, and they have a Curie point at 50 degrees C. When exposed to an oscillating magnetic field (90 kHz, 50 Oersted amplitude), these seeds show a sharp drop in the rate of heat production at temperatures above the Curie point. In a simulated treatment of a small visceral mass that had negligible blood flow, the tissue temperature stabilized at the Curie point of the alloy with good temperature homogeneity throughout the volume heated by an array of thermoseeds.