Heating Properties of a Resonant Cavity Applicator for Brain Tumor Hyperthermia: TM-like Modes Permit Heat Production without Physical Contact

Abstract

This paper describes a potential new method to non-invasively heat a region in a human brain by using electromagnetic field patterns generated inside a resonant cavity and does not require any physical attachments to the subject. The purpose of the study described here is to demonstrate the ability of this method to heat a small defined region. This study utilized computer simulations and a current model of the new heating system. In this proposed heating method, a human head is placed in the gap of a re-entrant type resonant cavity. The brain tumor is heated through interactions with electromagnetic energy, and no contact is required between the surface of the head and the inner electrodes. The thermal properties of this proposed method when applied to agar phantoms were calculated with computer simulations, and these properties were checked experimentally with the current physical version of the heating system. The calculated temperatures were in close agreement with the measured temperatures with an error of 10% or less. The TM-like modes are similar to the transverse magnetic (TM) modes generated inside a cylinder type resonant cavity. To heat a defined region, two TM-like modes were tested on agar phantoms. The thermal images of the cylindrical agar and the agar head phantoms showed that the values for the temperature increases at the center of the heated agar phantoms using two modes, a TM010-like mode and a TM012-like mode, were 5.9°C and 8.0°C, respectively. The TM010-like mode resulted in a larger area being heated than the TM012-like mode. In experimental results, compared to the TM010-like mode, the heated area with the TM012-like mode was localized to approximately 50% of the area heated by the TM010-like mode. These results suggest that the proposed heating method using electromagnetic field patterns generated inside of a resonant cavity is capable of being used for non-invasive brain tumor hyperthermia treatments.