ANALYSIS AND COMPUTATION OF LEAKY-WAVE HYPERTHERMIA APPLICATOR

Abstract

The use of electromagnetic waves to induce hyperthermia in cancer therapy has been the subject of intensive research but obtaining good resolution at depth in the abdomen and pelvic regions remains a fundamental problem. This paper investigates the prospects for generating leaky-waves in tissue to improve field penetration and focussing at depth. An approximate analysis based on a planar structure illustrates the feasibility of obtaining good resolution at depth but leaky-wave action in a strict sense is not possible. Measurements on an applicator conformal with the phantom tissue simulated by a saline solution, demonstrate good resolution and penetration but hotspot regions are detected around the launcher region. A three dimensional finite difference time domain (FDTD) computation is performed in Cartesian, circular cylindrical and elliptic cylindrical coordinates to model all the effects for various geometries of the phantom region and different launching symmetries. The results illustrate the need for symmetric launching of the strip, computational convergence and mode diagnostic data, the shape of the focal region and the useful property of being able to shift the focal region by changing frequency. It is concluded that this new quasi-leaky-wave applicator concept is potentially capable of giving improved focal resolution at depth with some positional control and only one generator is required. Optimising the launching of the quasi- leaky waves on the applicator and preventing hotspot regions from creating unwanted tissue heating are remaining practical problems to address. [Vol. 7, No. 2, pp. 72-84 (1992), Special Issue on Bioelectromagnetic Computations]