Design of intracavitary microwave applicators for the treatment of uterine cervix carcinoma.

A 915 MHz intracavitary applicator was designed to heat tumours in the cervical and upper vaginal regions. The applicator has a 3.5-turn helical coil wound around the distal 19 mm of a dielectric rod 43 mm long and 30 mm in diameter. For treating uterine cancer, a 2450 MHz, 4 mm diameter helical applicator was made by replacing 6 cm of the outer conductor of a coaxial cable with six turns of copper wire soldered to the outer conductor. The heating patterns were determined thermographically in a muscle phantom. The maximum heating rates were 0.42 and 0.83 degrees C/W-min, respectively, for the 915 and 2450 MHz applicators. Intracavitary temperature distributions in the upper vagina, cervix and uterus were measured at the surface of the applicators with thermocouples. The average temperature was 46.0 +/- 2.1 degrees C (S.D.) at mid-tumour and 44.5 +/- 0.8 degrees C at the tumour periphery. The maximum temperature, up to 51.5 degrees C, was measured at the surface of the cervical applicator. The majority of the patients (28/30) tolerated the investigational treatment without burns or pain. Rectal temperatures were also monitored. The location of the hot-spot (40.7 degrees C) in the rectum, 5-7 cm above the anus, corresponded to the tip of the cervical applicator (47.1 degrees C).