Radio Frequency Magnetic Induction Hyperthermia

For heating deep seated tumors, many attempts have been made to optimize the development of RF applicators of frequencies low enough to obtain a better penetration, while trying to confine the controlled volume into limited sizes. Magnetic induction applicators have high application potential due to their non invasiveness, to the little skin overheating espected and to the practicality of the electromagnetic coupling with the body. We have developed a class of 27 MHZ magnetic induction applicators (1,2) consisting of two single magnetic dipoles forming a loosely coupled pair (Twin-Dipole) fed by low-frequency, in-phase currents, giving defined heated volumes at intermediate depths due to the effect of phase coherence of both superimposing fields. The results show a penetration depth up to 7 cm and a power deposition pattern exhibiting a well defined maximum which may undergo a controlled shift of a few cm in depth. Moreover, the surface overheating is easily controlled. Low frequency RF inductive applicators produce current loops in the body, and their power deposition pattern depends strongly on the body dimensions and symmetry and on the body-applicator configuration. With the aim of controlling the penetration depth of the Twin Dipoles e have designed and tested a variety of versatile multiple applicator systems employing both active and passive RF auxiliary circuits (3). These systems exploit the coherence effect of the superimposing fields on the controlled volume, in analogy with the phased array technique (4) The results show a significant improvement over single applicators. (1) C. A. Tiberio, L. Raganella and C. Franconi, "symmetric pure induction 27 MHZ applicator", in proc, 2nd Int. 1 Conf, Applications of physics to Medicine & Biol., C. Franconi et al. (Eds), P. 585, World science publ., 1984. (2) L. Raganella, C. Franconi, C.A. Tiberio and 1. Begnozzi, :Linear induction applicator", presented at the 1984 Int.1 symp. (iV) on Hyperthermic oncology, Aahrus, DK, July 2-6, 1984. (3) L. Raganella, C. Franconi, C.A.Tiberio and L. Begnozzi, "RF Induction Applicators III-Twin Dipole with auxiliary circuits", proc. VII ESHO Meeting, Paris, 1985. (4) C. Franconi, C.A.Tiberio, D.Raganella, and L. Begnozzi, "Low-Frequency RF Twin-Dipole Applicator for Intermediate Depth Hyperthermia", in IEEE Trans. MTT vol, 33, Issue on phased Arrays for Hyperthermia treatment of cancer, 1986, in press.