A technique for producing localized measurable hyperthermia in superficial rat tumours using ultra-high frequency currents

Abstract

An increasing amount of evidence is becoming available from in vitro studies to indicate that elevated temperatures can enhance the damaging effect of ionizing radiation (e.g. Ben-Hur et al., 1978). In this communication we describe a technique which allows the extension of such work to in vivo studies on rodents. Localized hyperthermia has been produced in tumours on the flanks of rats by the flow of an ultra-high-frequency current at 433.92 MHz. In addition, under our experimental conditions it has been possible to monitor the tumour temperature during heating. As the work described here forms part of a project to assess the usefulness and feasibility of hyperthermic treatment of human cancers, the choice frequency was based on its suitability for producing deep heat in man. Radiofrequency power can introduced into the body in several ways. An electric field may be applied in a direction predominantly normal to tissue interfaces, as in short-wave diathermy. As a consequence of the boundary conditions and the electrical properties of tissues, such a technique results in a higher rate of heat production in tissues with low water content such as fat and bone than in those containing more water such as muscle. In contrast, microwave diathermy produces electric field which is predominantly parallel tissue interfaces. With this orientation of the electric field, fat and bone become relatively transparent to the radiation, with the advantage, therefore, that most of the energy is deposited in tissues with higher water content.