Development of 3-D phased array applicator for deep-body hyperthermia: FDTD modeling and experimental verification

Deep-body hyperthermia (HT) therapy is based on selective overheating of tumors using the constructive interference of E-fields irradiated from an HT applicator and polarized along the patient axis. Present HT applicators for the pelvis and abdomen operate at frequencies between 70 and 120 MHz. The interference patterns are often disturbed by hot-spots at tissue interfaces. Numerical studies have shown that these hot-spots can be better resolved when 3-D instead of 2-D phase and amplitude control is applied. However, a simple axial segmenting of antennas for obtaining a 3-D applicator results in their reduced efficiency (antenna mismatching. high normal E-field, inter-channel coupling). Thus, efforts are necessary to overcome these problems. Another important precondition for further development of deep-body HT is a noninvasive monitoring of temperature in patients under treatment using magnetic resonance (MR) methods. Therefore, an interaction-free combination of HT applicator and MR tomograph is necessary. This means reduction of cross dimensions, avoidance of metal surfaces and loops as well as an absolute ban of ferromagnetic materials. The aim of this contribution is to present, how antenna structures can be geometrically shortened without sacrificing the high performance required for the MR compatible 3-D phased array applicator for deep-body HT.