Evaluation of Neutron Dose Distribution for the Cyclotron

醫用迴旋加速器誘發中子之劑量評估

丁健益(Chien-Yi Ting)；賴律翰(Lu-Han Lai)；林招膨(Jao-Perng Lin)

迴旋加速器 ； 中子劑量 ； 氣泡式偵檢器 ； Cyclotron ； Neutron Dose ； Bubble Detector

台灣應用輻射與同位素雜誌

9卷3期（2013 / 09 / 01）

715 - 719

英文

正子斷層掃描（Positron Emission Tomography, PET）所需的短半衰期放射性藥物由迴旋加速器（Cyclotron）生產，國內目前有十座迴旋加速器在負責生產。迴旋加速器在製造放射性藥物時，過程中質子射束撞擊靶除了產生γ、β輻射，亦額外產生中子。此中子輻射若輕忽不加以注意容易使工作人員直接或間接造成體外輻射劑量。本研究主要評估迴旋加速器運轉時所誘發中子劑量。研究儀器為氣泡式偵檢器，此偵檢器為國際輻射防護委員會（International Commission on Radiological Protection, ICRP）所推薦之中子劑量計，量測方法為分別佈點於迴旋加速器周圍四個方向並劃分為A、B、C、D區域，總共12個偵測點。研究結果顯示，最大之中子劑量為A區，劑量率為9.6 μSv/h。數據結果指出，迴旋加速器室中子等價劑量分佈為距離平方的倒數。透過本研究結果可瞭解中子劑量分佈與方向性、距離的關係，此研究結果可供國內迴旋加速器中心輻射安全評估做為參考。

There are ten medical cyclotrons in the production of radiopharmaceuticals in Taiwan. The radiopharmaceuticals were obtained from the nuclear reaction when the target is bombarded with a proton beam. This reaction produces the neutron field around the cyclotron. The neutrons that were emitted from (p, n) reactions directly or indirectly caused hazard to the health of medical personnel and the public. We aim to evaluation of neutron dose distribution for the medical cyclotron. The bubble detectors were used to measure the dose contributed from neutron, which is sensitive to neutrons. The method of bubble detectors were used to evaluate the dose distributions contributed by neutrons in the cyclotron room during the operation. Bubble detectors were positioned at twelve points located along four directions around the cyclotron, respectively.The dose distribution of neutrons in the cyclotron room was estimated by using bubble detectors. The maximum neutron dose rate of 9.6 μSv h^(-1) appeared at A area. The result of data indicate that the neutron dose distribution decrease with the inverse square of the distance. The neutron equivalent dose decreased with increased distance to cyclotron. By means of the results of this measurement, neutron doses contributed from different directions and from different distances in the medial cyclotron room were realized in this study.