Simulation Study of Lens Applicator for Hyperthermia Treatment

Abstract

In this paper, a lens based applicator is designed with the enhanced focusing ability for hyperthermia treatment. The lens applicator consists of a stacked double spiral antenna (DSA) and frequency selective surface (FSS). The FSS structure behaves as a lens that converts the bidirectional field pattern into the directional pattern which improves the focusing ability of the proposed antenna towards the phantom. The double spiral structure is designed on the top of the upper substrate (Substrate-1), the slotted ground plane is placed between the upper and lower substrate, and the microstrip feed line is printed on the bottom of the lower substrate (Substrate-2). The overall size of the double spiral antenna is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$32 \times 32\times 3.27\ \text{mm}^{3}$</tex> . Moreover, an FSS structure (as a lens) is designed on RT- duroid substrate having a thickness is 1.575 mm and the size of a unit cell of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$16\times 16\ \text{mm}^{2}$</tex> . The size of the superstrate is optimized for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$64\times 64\ \text{mm}^{2}$</tex> which consists of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4\times 4$</tex> unit cell. It is placed at a distance of 8 mm above the stacked double spiral antenna. The lens applicator is simulated with heterogeneous phantom (skin, fat, and muscles) and the performance of the applicator is evaluated by using a specific absorption rate (SAR) in terms of penetration depth (PD) and effective field size (EFS). Further, the performance of the applicator is also analyzed for a deep placed (at 16 mm from the skin surface) tumor having a size <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20\times 20\ \text{mm}^{2}$</tex> .