A field-focusing device to increase power output of ThermoRod™ implants for thermal ablation of tissue

Abstract

Induction heating of small, cylindrical ferromagnetic implants (1.4 cm long and 1 mm in diameter) is a method for treating deep-seated tumors. These implants, or ThermoRods™, are placed within a lesion in 1-cm2 arrays and are exposed to an alternating magnetic field. The implants absorb energy from that field and transfer it as heat to the surrounding tissue. Each ThermoRod™ offers approximately 400 mW of power, and to kill cells, the target temperature must be greater than 42 °C. In this work, a magnetic field-focusing device is employed to concentrate the induced magnetic flux toward a local region near the base of the prostate to increase the power output of proximal ThermoRods™. This, in turn, allows for more complete thermal ablation of lesions near the base of the prostate where the heat-sink characteristics of the bladder can cause significant power losses. Boundary element analysis and in vitro testing have shown that the use of a ferrofluid-based field-focusing device can lead to a significant increase in power output of approximately 25% and 13%, respectively, of proximal ThermoRods™. These preliminary results indicate that the incorporation of such a ferrofluid-based focusing device into ThermoRod™ treatments is promising for the avoidance of significant power loss and for assuring complete thermal ablation of prostatic lesions. © 2002 Wiley Periodicals, Inc.