應用於質子治療之射束監測系統的特性研究

Performance Study of a Beam Monitoring System for Proton Therapy

戴淑眞(Shu-Jhen Dai)

指導教授 ： 林宗泰

國立中央大學/理學院/物理學系/碩士(2011年)

摘要

在未來幾年，質子治療中心將在台灣開始營運。一個可靠的射束監控系統對於質子治療設備的日常運作是不可或缺的。透過客製化電路，標準的16通道條型游離室以及多層法拉第杯遂用於此一目的。在本研究中，我們主要針對深度對劑量的分布、射束的剖面劑量以及射束的能量作量測。
在核能研究所以及日本東北大學迴旋加速器及同位素中心，我們對條型游離室的基本性能進行量測。利用不同厚度丙烯腈－丁二烯－苯二烯共聚物（ＡＢＳ），可以得到深度對劑量的分布曲線（布拉格曲線），實驗數據與Geant4模擬的結果相當吻合。因為條型的設計，空間上射束隨深度擴張的情形也可以被觀察到。另外利用Ｘ和Ｙ方向交替排列的六個游離室，已經初步可以得到類３－Ｄ的射束在不同深度剖面圖。
我們利用多層法拉第杯量測出日本東北大學迴旋加速器及同位素中心使用的射束能量。方法是利用一組相同的射束能量與能量範圍通過不同厚度的銅塊，將多層法拉第杯量測到的數據，透過最大似然法則與Geant4模擬結果相比較，得到最好的結果為77.8 ± 0.1 MeV，這結果與日本東北大學利用核磁共振探針量測到的結果相當吻合。

關鍵字

質子治療 ； 射束監控系統

並列摘要

Proton therapy facilities will be in operation in Taiwan in few years. It is important to have a reliable beam monitoring system for daily operation. A prototype 16-channel strip ionization chamber with custom-design readout electronics and a multi-layer Faraday cup have been developed for this purpose. In this study, three aims are measuring the depth-dose distribution, beam profile and beam energy.
The characteristics and performance of the ionization chamber have been studied using the beam at the Institute of Nuclear Energy Research (INER) and the Cyclotron and Radioisotope Center (CYRIC) of Tohoku University. The depth-dose distributions (Bragg curve) of protons in Acrylonitrile Butadiene Styrene (ABS) are obtained and the results agree with the Geant4 simulation well. Beam spread with depth is measured. The quasi 3-D beam profile with 80 MeV proton beam at CYRIC are measured by six ionization chambers arranged in X- and Y-direction alternatively.
Beam energy used at CYRIC is measured with the multi-layer Faraday cup (MLFC). A set of beam energy and its spread, by passing the beam through copper block with various thicknesses, is measured with the MLFC. The method of maximum likelihood is used to fit the data with the GEANT4 simulation. The best result obtained is 77.8 ± 0.1 MeV, which agrees well with the NMR probe measurement.

並列關鍵字

proton therapy ； beam monitoring system

參考文獻

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