A family of 27 MHz heating devices has been developed and fundamental tests carried out. The devices consist in a pair of ring-like, flexible, capacitive electrodes, conformally wrapped round the tissue to be heated, for use in hyperthermia and rehabilitation treatment. These capacitive ring (CR) applicators produce an axial E-field which can uniformly heat the central portion of a 20 cm OD cylindrical phantom simulating fat and muscle tissues. This electrode-body configuration can be used to uniformly heat most human body segments with the highest symmetry congruence, the RF currents flowing parallel to the boundaries provided by the pseudo-axial symmetry of these segments. With respect to the rigid pads used in RF capacitive heating, the CR electrodes exhibit a larger working surface area. Moreover, they may be used with an interposed dielectric layer between the electrodes and the skin, to reduce edge effects. With respect to the axially symmetric radiators of higher frequency, they are applicable to larger cross-section body segments with increased penetration and without the need of an integral water bolus. The CR devices allow free access to most of the body surface for skin temperature measurement and conditioning, and for combined treatments. Moreover, the almost uniform heating pattern may represent a useful feature for standardizing treatment. The CR electrodes can easily be matched to the RF source even if they are low impedance devices, and they give rise to low-level stray fields, which can be taken care of by a local shield. These CR devices can be considered safe and practical and suitable for regional hyperthermic and rehabilitation treatment.

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A novel low RF frequency hyperthermia applicator is presented. This consists of a toroidal resonator on the conductive wall of which two radical treatment ports are cut away to generate an air gap. This exposes the body part to be treated to the RF magnetic field fluxtube of high density and uniformity that is circulating uninterrupted within the toroidal walls through the air gap. The configuration of the port-body assembly may be adjusted for steering the induced heating field over the target while maintaining the effectual energy coupling with the tissue. The results of the assessment of a 27 MHz high density fluxtube on cylindrical all-muscle and fat-muscle phantoms show that a purely inductive type of heating occurs, which is substantially localized inside the muscle tissue and a water bolus is unnecessary in the absence of stray E-fields. Heating field optimization is accomplished with fluxtube cross-section, pathway and air gap shaping. It is also shown that the superimposition of a uni-directional coherent field created by passive auxiliary electrodes to the fluxtube-induced solenoidal field produces a constructive interference and enhanced and more penetrating localized heating.