| BackgroundEsophageal carcinoma is one of the most malignant neoplasms in digestive organs. Patients with early stage are mainly treated by surgery alone and will have a 90% to 100% survival at 5 years, while for the most patients with Middle-late stage are treated by chemotherapy and radiotherapy and only have a 25% to 30% survival at 5 years. The main treatment failures are local recurrences and metastasis. So, how to enhance the curative effect of medium-term and advanced esophageal carcinoma is a much-talked-about subject in medical community. As one of the treatments for esophageal carcinoma, intracavitary hypothermia has played an important role and drawn more and more peoples` attention. According to the latest documents, hypothermia combined with surgery,chemotherapy and radiotherapy increase the clinical complete response and long-term survival. At present, the structure of applicators used in intracavitary hyperthermia for esophageal carcinoma is single grade coaxial cable structure, and their effective heating length is 10cm at most. So, for the lesions that are longer than 10cm, these applicators can not meet the requirements. Besides, due to the uneven distribution of heat sent out from the applicator, the temperature difference aggravates as the time goes on. Therefore, how to increase the microwave intracavitary applicator's effective heating length? How to make the heat distribution more homogeneous? These problems are needed to be solved in order to improve the quality of intracavitary hypothermia of esophageal carcinoma.Objective1. The aim of this study is to explore if the method of"Moving the microwave applicator to and fro while heating"could increase the effective heating length and make the heat distribution more homogeneous.2. To explore the influence of matching relation between heating power,moving distance and moving speed on the heat distribution.Material and Methods1. The microwave radiator antenna, a single grade coaxial cable structure, is 1.5 meters long and 2 millimeters in diameter and its effective heating length is about 4cm.Set the maximum output power at 10w.The moving distances of the radiator antenna are divided into three groups:6cm,8 cm,10cm. Start the microwave hyperthermia machine and move the radiator antenna to and fro in the plastic conduit at a constant speed of 6 centimeters per second with a distance of 6cm for 2minutes continually. Then record the color display on the liquid crystal thin film and the temperature values obtained by the fiber-optic temperature measuring line immediately, and then draw out the SAR. Using the same method, measure the color display and SAR distribution when the moving distance is 8 cm,10 cm, respectively.2. Remaining the heating power at 10W, measure the color display and SAR distribution when the moving distance is 6cm,8cm,10cm respectively with the moving speed increasing to 12cm per second for 2 minutes.3. Adjusting the heating power to 20W and keeping the moving speed at 12cm per second for 2minutes, measure the color display and SAR when the moving distance is 6cm,8cm,10cm respectively with the same method.Results1. The radiator antenna's effective heating length is about 4 cm when it works with a fixed position. How, the effective heating length increases to 8.8cm,11cm and 12.5cm respectively when the radiator is moved to and fro with a distances of 6cm,8cm and 10cm at a constant speed of 6cm per second with the microwave hyperthermia machine's maximum output power set at 10W. Besides, the heat distribution is more homogeneous than that when the radiator antenna works with a fixed position.2. Keeping the heating power at 10W and raising the moving speed of the radiator antenna to 12cm per second for 2minutes, the highest temperature value is 42.6℃,40.4℃,39.6℃respectively when the radiator's moving distance is 6cm,8cm and 10cm. Besides, the temperature rises faster and the heat distribution is more homogeneous than that of moving speed at 6 cm per second.3. Keeping the moving speed of the radiator antenna at 12cm per second and adjusting the heating power to 20W for 2minutes, the highest temperature value is 46.6℃,43.8℃,42.6℃respectively when the radiator's moving distance is 6cm,8cmand 10cm. Moreover, the temperature rises faster and the values are higher than that of heating power set at 10W.Conclusions1. The heat distribution of the microwave hyperthermia radiator used in our experiment is like"Peaks form"in the axial direction and is like"Concentric shape"in the radial direction.2. No matter how much the power is, as the time goes on, the overheating points appear. So, it is difficult to achieve uniform temperature distribution using the continuous heating without changing the antenna's position.3. It's feasible to increase the effective heating length and make the heat distribution more homogeneous by moving the radiator antenna to and fro at some constant speed. In this experiment, the effective heating length increases to 8.8cm,11cm and 12.5cm when the moving distance is 6cm,8cm and 10cm respectively. But the effective heating length obtained by changing the radiator antenna's position is not equal to the geometric sum of its inherent effective heating length and the moving distance.4. The matching relation between moving distance,moving speed and heating power plays a significant role in the uniformity of heat distribution. When the moving distance and moving speed remain unchanged, the greater the power is, the faster the temperature rises. Similarly, when the moving distance and heating power remain unchanged, the faster the moving speed is, the faster the temperature rises and the more homogeneous the heat distribution is. It requires increasing the moving speed and heating power when the moving distance increases in order to make the heat rise more rapidly and the heat distribution more homogeneous.5. The microwave radiator antenna is the key device in hyperthermia. However, the manufacturer barely provides the SAR of the radiator antenna or the difference between the provided SAR and the SAR obtained from actual measurement is enormous. So, it is necessary to survey the heat distribution of the microwave radiator antenna before we carry out a treatment in the clinic. |
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