Focal heating of V-2 tumors with a hybrid radiofrequency applicator.

A hybrid radiofrequency heating system previously reported to produce highly focused heating patterns at less than or equal to 10 cm depth in phantom models was utilized to selectively heat hypervascular, heat resistant rabbit V-2 tumors implanted in the left hindlimb. Spheroidal heating patterns 3 to 4 cm in diameter with minimal temperatures of 43 degrees C to 46 degrees C in two non-field perturbing probes at opposing edges of the tumor were consistently produced; however, temperature maxima 0.5 +/- 0.4 to 8.6 +/- 5.9 degrees C above minimum target temperatures of 43 degrees C and 46 degrees C, respectively, were observed. This led to both tumor regressions and adjacent normal tissue damage in some animals. These findings suggest this system may have application to selective heating of deep seated tumors, but that problems related to accurate thermal mapping and to intratumor temperature distribution must first be resolved.