開發適用於游離腔之微小電流即時量測系統

Implementation of a Real-Time Current Measuring System for Ionizing Chamber Use

洪榮鴻(Rong-Hung Hung)

指導教授 ： 鐘太郎

國立清華大學/電機資訊學院/電機工程學系/碩士(2014年)

摘要

近年來治療癌症的方式越來越多元，其中放射治療可分為光子治療與質子治療，對此醫院中都配備品保儀器，例如以小型游離腔室搭配量測儀器，作為輻射量測工具。劑量是由帶電粒子(電荷)及電流轉換而來，如果可以量測出電流的強弱，就可以推算出應施打的劑量，因目前核研所的量測儀器以電流積分器為核心架構，價格昂貴、積分時間長。本論文就是致力於開發一套以轉阻放大器為核心，適用於游離腔之微小電流即時量測系統，此系統可降低系統開發成本及量測時間。
本系統有使用到的硬體架構有圓球型游離腔、轉阻放大器、ADC、MCU(MSP430)、RS-232轉USB連接器及一台PC，當放射源穿過游離腔，會游離出正離子和電子，游離腔內殼有高壓板，易於電荷收集而形成電流，電流經轉阻放大器轉為電壓訊號，ADC將類比電壓轉為數位電壓，驅動硬體指令由MSP430控制，訊號經RS-232轉USB連接器傳回電腦，DAQ系統使用Labview軟體，控制資料擷取與分析，並即時顯示波形及溫度監測。
系統建構完成後，先使用電流源做測試，再到核研所實際以X光為放射源做量測，分別調控X光機的管電壓及管電流，管電壓設定為80kV、100kV、120kV、150kV，管電流設定為5mA、10mA、15mA、20mA、25mA、30mA，皆可正常量測到游離腔的電流，經校正後和核研所量測儀器做比較，誤差最多為1%左右，證明使用本系統確實適用於游離腔之微小電流即時量測系統。

關鍵字

游離腔 ； 微小電流量測 ； MSP430 ； Labview

並列摘要

There are many treatment options for cancer, with the primary ones including surgery, chemotherapy, radiation therapy, etc. In this study, we pay great attention to radiation therapy, which is a kind of particle therapy. Some quality assurance instruments, such as ionizing chamber associated with measuring instruments, are used for radiation measurement use. With the measurement of the weak current output from the ionizing chamber, the radiation dose can be estimated. The central architecture in the measuring instrument is current integrator. While current integrators are usually expansive and slow, in this thesis, a low-cost real-time current measuring system for ionizing chamber using trans-impedance amplifier as central architecture is proposed.
The proposed system includes a trans-impedance amplifier (TIA), a MSP430 board, and a PC. TIA detects and converts the received ionized electrons in the ionizing chamber generated by radiation beam into voltage signal. Then, the analog to digital converter (ADC) on the MSP430 board converts the analog voltage signal into digital form. In the end, the digital voltage signal is transmitted to the PC via RS-232 to USB interface. A control program is developed for MSP430 to control the data acquisition task while a Labview-based DAQ/GUI program is developed on PC, which displays real-time waveform and detects temperature.
The proposed system is tested and justified with the discrepancy smaller than 1%. The experimental result show that our system has achieved the anticipated goal and can run in a practical situation.

並列關鍵字

Ionization Chamber ； Current Measuring

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