Preliminary Tests of Local Hyperthermia Based on Inductively Heated Tumor Bed Implant

Abstract

Hyperthermia, i.e. tissue heating to a temperature of 39-45°C, is considered to be a very promising technique to increase the sensitivity of tumor cells to ionizing radiation and chemical preparations. At the present time, there are numerous methods for producing hyperthermia with the optimum method dependent on the required volume, depth, and site of heating. This paper presents the results of preliminary theoretical and in vivo confirmation studies of the feasibility of intraoperative local hyperthermia via induction heating of ferromagnetic material within a tumor bed implant that fills a resected tumor cavity. The implant is made during the surgical removal of tumor by mechanically filling the tumor bed with a self-polymerizing silicone paste in which very fine electroconductive ferromagnetic particles are uniformly distributed. Therefore, the implant can accommodate unique characteristics of each patient’s tumor bed. For the laboratory experiments, a prototype induction heating system was used to produce an alternating magnetic field with a frequency of about 100 kHz and a maximum intensity up to 3 kA/m inside an induction coil of inner diameter 35 cm. Experiments were conducted to heat a 2.5 cm diameter spherical implant both in open air and inside the thigh of a living rabbit. The results in both cases are in good agreement with our theoretical estimations. It was established that the temperature gradient near the implant surface decreases with increasing implant size, and for typical size tumor bed implants produces effective hyperthermia to a distance of more than 5 mm from the implant surface. This result provides hope for a decrease in relapse after treatment of malignant tumors using our combination heat plus intraoperative high dose rate local radiotherapy approach. Moreover, the externally coupled implant heating can be combined with local chemotherapy by applying a self-resorbable polymer film containing antineoplastic agents to the surface of the implant.