Power loss in skin cooling pillows during RF hyperthermia

A variety of methods is available for dissipating electromagnetic energy in human tissue to induce hyperthermia for the treatment of cancer (Hand & ter Haar, 1981). One method is capacitive coupling using shortwave frequencies: commonly 13.56 or 27.12 MHz. This method is suitable for heating large volumes at depth. However, because of the high current density near the electrodes, excessive heating of the surface tissues can occur. The problem is exacerbated by the presence of a thick layer of subcutaneous fat, since this has relatively low values of electrical conductivity and dielectric constant, and a relatively poor blood supply compared with the tissues of higher water content deeper in the body (Guy et al, 1974; Hahn et al, 1980; Hand & ter Haar, 1981). It is, therefore, standard practice to reduce this surface heating by positioning flexible pillows perfused with cooled deionised water or saline between the electrodes and the skin (Carnochan & Jones, 1982; van der Zee et al, 1982; Kato et al, 1983; ...