Research On The Method And Device For Monitoring The Output Power Attenuation Of Microwave Hyperthermia Apparatus

Microwave hyperthermia has been made more widely used in clinical treatmentof tumor. The microwave output power is an important parameter in microwavehyperthermia apparatus. The accuracy of output power is directly related to the clinicsafety and efficacy. Usually, the output power of microwave hyperthermia apparatushas one to one relationship with the anode current of magnetron. So the microwavepower can be achieved by measuring the magnetron anode current. But in actual use,the aging of the microwave magnetron would cause the original scaling functionrelationship changes,which inevitably leads to the power measurement error, thenresults in decreasing clinic efficacy, and even medical Malpractice. Therefore,monitoring the output power attenuation any time and correcting the actual outputpower in time is particularly important. However, the existed method and process ofmicrowave power calibration is very cumbersome and complex. Once the relationshipbetween the output power and magnetron anode current changed, it is difficult tore-calibration in the hospital scene. This would be very detrimental to the clinicalapplication of microwave hyperthermia apparatus.To solve this problem, a half-wave dipole antenna is combined with a low-barrierSchottky diode to build a microwave power sensor. The spatial distribution of outputmicrowave power density of the microwave hyperthermia apparatus is investigated byusing this sensor. A conclusion is drawn that the spatial distribution of outputmicrowave power density is stable in time domain. Then the microwave power sensoris fixed in front of microwave radiator. The voltage of microwave power sensor ismeasured at different microwave power levels. Finally, the output microwave poweras a function of the voltage value of microwave power sensor is confirmed and theresults are stored in MCU system. With this relationship, the output power attenuationof the microwave hyperthermia apparatus can be easily monitored by measuringvoltage of microwave power sensor.From this point of view, with a single-ship computer ADuC832produced byAnalog Device Inc, a device for monitoring and calibrating the output microwavepower has been designed and developed，in which including hardware and softwareparts. The hardware part consists of power signal acquisition circuit, amplifier, A/Dconversion circuit, microcontroller circuits, LCD display and keyboard circuits. The software part is divided into several program modules, which are LCD programmodules, keyboard scanner module, signal acquisition program modules, mainprogram module. The power calibration program and power measurement program areincluded in main program module. Through a large number of experiments using thedeveloped equipment in full range to measuring the actual output power of microwavehyperthermia apparatus, the maximal measurement error is less than5%. This methodwill be used for technical staff to correct the output power of microwave hyperthermiaapparatus in time, and therefore to insure safety and effectivity in microwavehyperthermia.