Temperature distributions from interstitial rf electrode hyperthermia systems: theoretical predictions.

In recent years, there has been increased interest in the use of hyperthermia as an adjuvant modality to radiation and chemotherapy in the treatment of cancer. One of the more promising techniques is the application of an rf voltage to an array of electrodes inserted directly into the tumor. The electrodes are usually small, hollow stainless steel needles that are inserted as the first step in a brachytherapy procedure. By applying a voltage between the needles, an rf current is induced in the tissue, resulting in joule heating. In this paper, we calculate numerically the temperature distributions for an array of such needles. In our model we assume a two-dimensional problem, i.e. infinitely long needles, and a homogeneous medium. Blood flow effects are included in the calculation. The results show that for low blood perfusion rates, e.g., on the order of 3 ml/100 gm X min, very smooth temperature distributions result, and the electrodes can be spaced fairly far apart. However, for blood flow rates on the order of 20 ml/100 gm X min the temperature distributions are not smooth, and there are hot spots around the electrodes and cool regions between them. However, if the electrodes are spaced about 1 cm apart and the voltages are adjusted to optimize the temperature distribution then reasonably good results should be achievable. The equation is solved using a finite difference technique. By applying the superpostion principle, we are able to introduce a procedure which substantially reduces the amount of core storage required and results in reasonably efficient run times on a moderate size mini-computer.