Development of interstitial antennas for hyperthermic treatment of cancer

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We have developed a microwave coaxial ring-slot applicator for interstitial hyperthermia in cancer therapy. The applicator is co-axial slots antennas made of a 0.86 mm outer diameter coaxial cable, and is used at a frequency of 400-430 MHz microwave. Several ring slots, which radiate microwave power into the surrounding tissue, are placed at equidistant intervals along this cable on the outer conductors, and the tip of the coaxial cable is short-circuited to expand the heating area around the tip of the applicator. The antennas can be inserted into a 21 G plastic catheter and the SAR distribution along them can be changed by ajusting the parameters of the slots. Multiple coaxial slots are arranged at short intervals on the outer conductor of the cable. Each antenna is loaded into a thin plastic catheter and an array of the antennas is then inserted into a tumor.The heating distributions characteristics of this applicator were investigated in the muscle-equivalent agar phantoms. The advantages of this applicator demonstrated were the relatively large haeting area and the relatively uniform heating area along the axis of the applicator. These advantages have been shown in animal experiments using the muscle and the implanted tumor. Histopathological examinations revealed massive coagulation necrosis of the tumors which were effectively heated with this applicater.The applicator was designed to be used with a 430 MHz microwave hyperthermia system, so that the temperature measurement and temperature control system equipped with the system are also availabel for the interstitial hyperthermia.