Development of coaxial-slot antenna for interstitial microwave hyperthermia

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・We have proposed to replace some elements of the coaxial-slot antenna array with parasitic elements to control the shape of SAR (Specific Absorption Rate) distributions. Coaxial-dipole applicator has sleeves on both sides of the single ring slot in its structure. Those sleeves are effective in restricting electrical field to distal area of the antennas.・The current distribution of coaxial-slot antenna has been derive by using moment method. This technique takes account of a dielectric cover and mutual between antenna elements that had ever been neglected.・Numerical simulation technique for near electric field of interstitial microwave antennas has been developed, and we have specified the behavior of SAR for the first time. In antenna array, dependencies of SAR distributions on arrangement of elements, feeding power and feeding phase for each element have been explicated. The mechanism of hot spot appearance nearby body surface has been clarified.・Experimental results with muscle-equivalent standard phantom developed in our laboratory have agreed with the above simulated results. This phantom has been recognized as the standard for microwave hyperthermia by the QA Committee in the Japanese Society of Hyperthermic Oncology.・For evaluation of the heating performance of hyperthermia applicators, the normalized SAR distribution [%] has been used as an index so far, which is unsuitable for microwave antenna. We have proposed the area of 43-centigrade at 10 minutes after the start of hyperthermia treatment as an index of heating characteristics evaluation considering the heat tolerance. Unmistakable correspondence between SAR value [W/kg] and therapeutic temperature has been confirmed if blood flow rate is identified. Temperature distributions have been calculated with finite-difference method.・For multiple coaxial-slot antenna that has more than one ring slot, current simulation by using moment method and transmission line theory has been proposed.