TUMOR CURE AND CELL SURVIVAL AFTER LOCALIZED RADIOFREQUENCY HEATING

Abstract

Radiofrequency electromagnetic fields at 13.56 MHz were used to heat locally EMT-6 sarcomas and KHJJ [mammary] carcinomas in BALB/cKa mice. Temperature profiles obtained in tumors during treatment showed uniform temperature distribution throughout the tumor volume with no systemic hyperthermia. Temperature could be maintained at a stable level throughout treatment by adjustment of power. Tumors were treated at 43.degree., 43.5.degree. and 44.degree. C for 5, 10, 20, 30 and 40 min. The EMT-6 tumor was sensitive to cure by radiofrequency heating: a 5 min exposure at 44.degree. C resulted in cure of almost 50% of the tumors. Cure rate was a function of temperature and duration of exposure. The KHJJ carcinoma was somewhat more resistant to cure by radiofrequency heating, although most of the animals treated at 43.5.degree. or above were cured of their tumors. In an effort to explain the remarkable effectiveness of radiofrequency heating, tumor cell survival studies were done on EMT-6 tumors treated in situ. Cell inactivation by radiofrequency heating was similar to that for hot water bath heating. Direct cell killing cannot account for the observed cures, and an additional mechanism must be responsible for tumor eradication.