Numerical Study On Microwave Heat-Therapy Of Benign Prostatic Hyperpasia

Benign Prostatic Hyperplasia (BPH) is a common disease of the urinary system, which afflicts the elderly. As the development of microwave technology, microwave hyperthermia of benign prostatic hyperplasia has been a common method of clinical therapy. Clinically, microwave heat-therapy need to reach the following two goals:(1) Enough microwave energy should be transferred to the target tissue and the temperature rises to a certain value to kill the abnormal tissue. (2) Normal tissue will not be injured during therapy. It will not cause the surface of the skin burned or other accidents. Therefore, microwave heat-therapy of benign prostatic hyperplasia is numerically studied through establishing mathematics physics model based on electromagnetic field theory and bio-heat transfer theory.In theoretical research, this paper introduces the distribution and calculation methods of electromagnetic field in near field and far field firstly. Then, the general formula of human tissues specific absorption rate is derived from the classical electro dynamics, which involves the Pointing vector and Maxwell equation.In the numerical simulation, aiming at the specific process of heating the prostate of the WR-intracavaty microwave therapeutic device, mathematics physics model is established by COMSOL Multiphysics to analyse the temperature distribution and electromagnetic energy distribution during therapy. The simulation results show that microwave energy is centralizedly distributed near the source. And microwave energy attenuates more quickly along the radial direction than axial direction. Meanwhile, the area of high temperature in the prostate is also distributed near the slot of microwave antenna. It displays a symmetrical distribution about the center of slot, which is in accordance with the SAR distribution.Then, the influences of microwave power (P), blood perfusion ratio (Wb), the temperature of cooling water (Tf) and heat transfer coefficient (h) on the thermal field distribution in the prostate are discussed. The results show that different values of these parameters not only impact the value of peak temperature but also change the position of it. Also, it can be found different blood flow will influence the time that the temperature field approaches stable. As for the different patients with BPH, the prostatic blood flow rate is usually different. To determine the optimal solution for them, orthogonal experiment design method is used in this paper. It is designed with three factors and three values including microwave power (P), the temperature of cooling water (Tf) and heat transfer coefficient (h). P is 35W,45W,55W. Tf is 10℃,15℃,20℃. h is 50W/(m2·℃),150W/(m2·℃),257W/(m2·℃). The following conclusions are drawn:1) when prostatic blood flow rate is 10mL/min/100g, the optimal solution is P=35W, Tf=10℃, h=257W/(m2·℃). The urethra isn't damaged and the thermal penetration in the prostate is 9.7mm.2) when prostatic blood flow rate is 30mL/min/100g, the optimal solution is P=55W, Tf=10℃, h=257W/(m2·℃). The urethra isn't damaged and the thermal penetration in the prostate is 9.4mm.3) when prostatic blood flow rate is 30mL/min/100g, the optimal solution is P=55W, Tf=15℃, h=257W/(m2·℃). The urethra isn't damaged and the thermal penetration in the prostate is 6.6mm.The temperature field, electric field, magnetic field and SAR can be successfully predicted by numerical study on microwave heat-therapy of benign prostatic hyperplasia. It has a great guidance on the design of scheme. Meanwhile, for the different patients with BPH, the severity of illness is variable. Therefore, further study should focus on the research on therapy process in accordance with severity. Through this work, more targeted heat-therapy parameters will be obtained.