Selective tumor heating by shortwave radiofrequency (RF).

Experimental solid tumors were treated in vivo with external high frequency dielectric heating to observe any heat selectivity between the tumor mass on one hand, and the subcutaneous tissue, muscle, and systemic temperatures on the other. Methylcholantrene-induced sarcoma cells were inoculated into the subcutaneous tissue or muscles of the posterior thigh of isologous Fischer rats. When the tumor mass reached the desired size, dielectric heating with a fixed frequency of 13.56 megahertz (MHz) was applied locally to the tumor-bearing area. All the periods of treatment were kept constant at 1 hour. Temperature was measured with thermocouple probes inserted directly into the tumor mass and the tissues lying within the electromagnetic field. Systemic temperature was monitored via a clinical mercury thermometer inserted into the rectum. Temperature recordings were taken at 5-minute intervals during which time the power was turned off in order to avoid the RF interference and to allow thermal equilibrium between the probes and the tissue. The results showed a high selective temperature gradient for the tumor mass as compared to the subcutaneous and muscle tissues when tumor masses were greater than 1.0 cu cm. No selectivity was detected in small tumors or in nontumor-bearing controls. Systemic temperature did not rise by these treatments. No tumor regression was observed at this dosage. Burns were noted in those animals in which normal tissue temperature rose above 43 C.