Experimental examination of a targeted hyperthermia system using inductively heated ferromagnetic microspheres in rabbit kidney

It is known that significant heating can be generated by magnetic hysteresi s effects in small ferromagnetic particles exposed to a rapidly alternating magnetic field. If such particles can be made to infiltrate the vascular b ed surrounding a tumour by intravascular infusion then it may be possible t o generate sufficient heating to destroy the tumour by hyperthermia. One of the constraints on such a technique is the limited amount of magnetic mate rial that can be delivered to a tumour via the intravascular route and the consequent heating that can be induced by this material. Here, we report on a series of experiments in which doses of microspheres containing differen t amounts of ferromagnetic material were infused into rabbit kidneys via th e renal artery with the aim of testing whether adequate tissue heating coul d be achieved using realistic concentrations of the embolised material. Hea ting rates were measured for each infused quantity under similar conditions with the animal alive and dead to examine the role of blood flow in the he ating process. The results show that tissue temperatures above the therapeu tic threshold of 42 degreesC can be readily achieved using this method with clinically relevant concentrations of microspheres in living tissue.