CURRENT SHEET APPLICATORS FOR CLINICAL MICROWAVE HYPERTHERMIA

Current sheet applicators (CSAs) are light-weight, small size applicat ors intended to be operated in array configurations. Their radiative f ields are induced by RF currents in a conducting sheet embedded a few millimeters below the dielectric covered aperture surface. In arrays, these elements can be used over breast lesions, for superficial head t umors, torso regions and other curved body sites where conformity to b ody curvatures is necessary. Our clinical prototypes are tuned to 434 MHz and have a bandwidth of almost 20 MHz, which accommodates the tuni ng and coupling changes due to site differences of the body, body move ment and tissue heterogeneities. The relative insensitivity of these u nits to air bubbles in bolus and scar tissues are attractive clinical features. The inherent linear polarization allows easy visualization o f the superposition of electric field vectors of each element of an ar ray, as well as provides deeper penetration on curved surfaces due to the electric field vector addition in the medium. In the case of a lar ge breast tumor, depth of heating of over 4 cm was achieved along the central axis of a 2 x 2 coherent array. Experimental evaluation of the se elements, leading up to their clinical implementation, is described in detail along with the results of a clinical example.