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mặc dù nhiệt độ vào thời điểm này vượt quá 70 C mà không có kiểm soát. Hơn nữa, nhiệt độ tại điểm quan sát # 2, được đặt 5,0 mm từ trục ăng ten, vượt quá nhiệt độ thấp nhất điều trị (42 C). Hình 5,36 cho thấy sự phân bố nhiệt độ tính toán trong các máy bay quan sát được xác định trong hình 5,34. | 194 Antenna Issues in Microwave Thermal Therapies 30 15 0 -15 -30 -30 -15 0 15 30 -30 -15 0 15 30 x mm x mm a Observation plane 1 b Observation plane 2 Figure 5.36 Calculated temperature distributions around the bile duct. although the temperature at this point exceeds 70 C without the control. Moreover the temperature at observation point 2 which is placed 5.0 mm from the antenna axis exceeds the lowest therapeutic temperature 42 C . Figure 5.36 shows the calculated temperature distributions in the observation planes defined in Figure 5.34. In this figure the white dotted lines indicate 42 C which is the lowest temperature for the treatment. These temperature distributions for which the minimum size of heating region by the on-off feeding control is chosen are the results at the steady state. From Figure 5.36 the diameter of effective heating region the region higher than 42 C is approximately 15 mm in the x-y plane. The heating pattern in the axial direction of the antenna can be controlled by shifting the antenna. 5.5 Summary In recent years various types of medical applications of microwaves have been widely investigated and reported. In particular minimally invasive microwave thermal therapies using thin antennas are of a great interest. Among them are interstitial microwave hyperthermia and microwave coagulation therapy for medical treatment of cancer cardiac catheter ablation for ventricular arrhythmia treatment thermal treatment of benign prostatic hypertrophy. In this chapter after describing the principle of hyperthermic treatment for cancer some heating schemes using microwave techniques were explained. Then a coaxial-slot antenna which is one of the thin coaxial antennas and array applicators composed of several coaxial-slot antennas were introduced. Moreover some fundamental characteristics of the coaxial-slot antenna and the array applicators such as the SAR and temperature distributions around the antennas inside the human body and the current .
