The development of microwave hyperthermia applicators

Two direct-contact microwave (915 MHz and 2450 MHz) applicators were designed and fabricated for localized hyperthermia treatments of solid tumors. The 2.45 GHz applicator can be attached to an X-ray machine head and used as a cone to deliver X-rays and microwaves simultaneously. The 915 MHz applicator has the capability of cooling the skin surface by circulating a dielectric liquid through a bag attached to the application end of the applicator. The temperature and the flow of the liquid can be controlled to achieve the desired skin temperature. The temperatures of the incoming and outgoing liquid through the bag were measured to determine the energy lost. Temperature distributions were obtained using a pig in vivo system with liquid crystal and thermocouple probes. Using the 2.45 GHz applicator the skin surface remained at the highest temperature and a very steep temperature drop was observed (3.5°C drop at a depth of 3 cm). Temperature distribution improved when the 915 MHz applicator was employed. The skin surface remained at a temperature 0.5° C lower than that of the tissue at 1 cm depth. A temperature drop of only 1°C was observed at a depth of 3 cm. An even better distribution was obtained when skin surface was cooled. Skin surface and tissue at a depth of 3 cm were elevated to the same temperature while the tissue at depth of 2 cm was raised to a temperature 1°C higher.