Numerical Simulation of Magnetic Induction Heating of Tumors with Ferromagnetic Seed Implants

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Abstract
Calculations based on the bioheat transfer equation have been carried out to determine the temperature distributions to be expected from the use of inductively heated ferromagnetic implants to heat deep-seated tumors. Two types of ferromagnetic implants are considered: constant power seeds, for example, those constructed from Type 430 stainless steel; and constant temperature seeds which pass through a Curie transition to the nonmagnetic state at a specified temperature. The temperature distributions are studied as a function of the size of the implant array, its geometrical relationship to the tumor, the density of implants within the array, and the blood perfusion characteristics of the tumor and its surrounding normal tissue. Two tumor models are considered: a uniformly perfused model which is indistinguishable from the surrounding normal tissue, and an annular perfusion model with a necrotic core surrounded by intermediately and highly perfused shells. Temperature distributions are considered acceptable if the minimum temperature in the tumor is greater than 42°C and the maximum temperature does not exceed a maximum allowable value (either 48 or 60°C). The results of over 200 combinations of the above parameters are presented in a compact format. General conclusions drawn are that the tumor should lie entirely within the implanted array if the tumor periphery is to be heated adequately, and that the constant temperature seeds, which are self-regulating in temperature, give better tumor temperature distributions.