Low-frequency RF hyperthermia. IV. A 27 MHz hybrid applicator for localized deep tumor heating

A novel 27-MHz dual-device applicator for noninvasively and safely heating tumor masses at depth is proposed. A substantially localized temperature gain is obtained by superimposing two delocalized low RF frequency and phase-coherent current distributions, which are launched to constructively interfere over a limited region encompassing the tumor volume. A hybrid applicator (HA), integrating one capacitive and one inductive heating device was developed and assessed on a 20-cm-diameter cylindrical fat-muscle phantom. The interference pattern is characterized by a deep broad specific absorption rate (SAR) maximum and by the disappearance of the central null SAR value typical of single inductive devices. An 80% SAR useful therapeutic volume (UTV) of a near-cylindrical shape of about 800 cm ³ was obtained with a penetration of 6-8 cm for the phantom surface, with a noncritical axial length of approximately 21 cm. The UTV may be somehow controlled in size and penetration. These results are obtained with the tissuelike medium surrounding the UTV heated uniformly and safely to a temperature pedestal below the therapeutic temperature with about half RF power values to each of the heating devices.