Heating patterns induced by a 13.56 MHz radiofrequency generator in large phantoms and pig abdomen and thorax

Heating patterns generated by a commercially available 13.5 MHz radiofrequency generator and induction coil hyperthermia system in human size phantoms and a 230 pound pig were studied using a multichannel computer-monitored thermometry system that is noninteractive in electromagnetic fields. The phantom studies were composed of synthetic muscle equivalent material and fresh tissue. The pig was heated in the regions of the upper abdomen and the midthorax, both under anesthesia and dead. The temperature was measured along fine penetrating catheters at 1 cm intervals in all experiments. In a homogeneous cylindrical phantom, under our measurement conditions, the temperature profile across the diameter is parabolic with marked superficial heating and essentially no central heating. In nonhomogeneous phantoms and in the pig, the symmetry of this profile was distorted but the basic pattern of marked superficial heating and nearly absent deep central heating remained. Blood flow in the living animal produced some thermal smoothing. It is considered probable that substantial radial temperature gradients will exist within eccentrically located human tumors heated with this device and that certain deep central tumors will be difficult or impossible to heat. Determination of its ultimate value for investigational; clinical hyperthermia studies will require accurate temperature mapping of tumors and normal tissues in various anatomic sites in comparison with other approaches to deep heating.