Ito Kimiteru, Nakata Yasuhiro, Matsuda Hiroshi, Sato Noriko
Department of Radiology, National Center of Neurology and Psychiatry.
Kaku Igaku. 2011 May;48(2):109-19.
In Japan, positron emission tomography has prevailed as a useful procedure for detecting malignancy, myocardial viability, and epileptic foci. Consequently, compact medical cyclotrons have been installed in many hospitals. However, reports about the dismantling or decommissioning of compact medical cyclotrons are rare. This report describes the series of steps involved in the decommissioning of a compact medical cyclotron that had been used to produce radioactively tagged substances over a period of fifteen years at the National Center of Neurology and Psychiatry in Japan. Additionally, this report describes the manner in which the radioactive waste was disposed.
The plan to decommission the cyclotron was comprised of three phases: a preliminary survey, the dismantling work, and a reports after the dismantling. We complied with the guidelines for the disposal of radioactive waste published by the Ministry of Education, Culture, Sports, Science and Technology.
The most radioactive material was the vacuuming foil used in the window of the target chamber, with a dose rate of 17 microSv/h (gamma rays) and 20 x 10(3) cpm (beta rays). The detected radionuclides were mainly 22Na, 57Co, 60Co and 65Zn. The total numbers of radioactive waste containers were thirteen 200 l containers and one 50 l container. We suspect that the long shutdown period of the cyclotron (more than one year) contributed to the decay of the radioactive waste because the amount of containers was smaller than the initial estimation.
The shutdown period of a cyclotron may play a significant role in reducing the amount of radioactive waste.
在日本，正电子发射断层扫描已成为检测恶性肿瘤、心肌活力和癫痫病灶的一种有用方法。因此，许多医院都安装了紧凑型医用回旋加速器。然而，关于紧凑型医用回旋加速器拆除或退役的报道却很少。本报告描述了日本国立神经精神中心一台紧凑型医用回旋加速器退役过程中所涉及的一系列步骤，该回旋加速器在15年的时间里一直用于生产放射性标记物质。此外，本报告还描述了放射性废物的处置方式。
回旋加速器退役计划包括三个阶段：初步调查、拆除工作以及拆除后的报告。我们遵守了文部科学省发布的放射性废物处置指南。
放射性最强的物质是靶室窗口使用的真空箔，剂量率为17微希沃特/小时（γ射线）和20×10³计数/分钟（β射线）。检测到的放射性核素主要有²²Na、⁵⁷Co、⁶⁰Co和⁶⁵Zn。放射性废物容器总数为13个200升容器和1个50升容器。我们怀疑回旋加速器的长时间停机（超过一年）导致了放射性废物的衰变，因为容器数量比最初估计的要少。
回旋加速器的停机时间可能在减少放射性废物量方面发挥重要作用。
