Design of Site-Specific Microwave Phased Array Hyperthermia Applicators Using 434 MHz Reduced Cavity-Backed Patch...

Cancers of the neck, breast, and lower extremities are common malignancies diagnosed in India with a higher incidence of advanced-stage disease. Phased array (PA) applicators reported for hyperthermia treatment (HT) of the breast have small focal region and high cross-coupling, and those reported for lower extremities provide regional heating and limited steering. In this study, we present the numerical design of site-specific PA applicators for HT of large solid tumors in the neck, breast, and lower extremities using a miniaturized 434 MHz cavity-backed water-loaded patch antenna. The fabricated antenna has 38 × 36 mm² aperture, more than 90% power coupling, 25 MHz bandwidth, and good agreement between simulated and measured specific absorption rate (SAR) in phantom. The site-specific applicators demonstrated less power reflection (<-17.9 dB) and cross-coupling (<-26.8 dB) for 5 mm inter-ring spacing. SAR indicators for 64 cc tumor at varying locations in simplified layered three-dimensional (3D) tissue models of the neck, breast, and leg showed average power absorption ratio (aPA_ratio ) ≥ 3.16, target to hotspot quotient (THQ) ≥ 0.57, 25% iso-SAR coverage (TC₂₅ ) ≥ 81%, and 50% iso-SAR coverage (TC₅₀ ) ≥51.8%. Simulation results of site-specific applicators for 3D inhomogeneous patient models showed aPA_ratio  ≥ 5.98, THQ ≥ 0.9, TC₅₀  ≥ 86%, and 100% TC₂₅ for all sites. It is concluded that the 434 MHz miniaturized cavity-backed patch antenna can be used to develop high-density PA applicators with 12-24 antennas for HT of large solid tumors (≥4 cm) in the neck, breast, and lower extremities with 3D steering ability and less cross-coupling (≤-26.8 dB). © 2020 Bioelectromagnetics Society.