Standardization of Activation Evaluation for Decommissioning of Medical Cyclotron

Over the past several decades, various types of accelerators have been installed and operated worldwide, mainly for nuclear research and radioisotope production. Among them, the cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in the United States in 1934. It has been the best source of high-energy beams for nuclear physics experiments for the past several decades, and has been used to produce various radioisotopes used in diagnostic imaging such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), as well as in brachytherapy and alpha particle therapy. However, cyclotrons are being dismantled and decommissioned domestically and internationally due to reaching their design life or due to aging, accidents, or other reasons, and there is no standardized technical or administrative procedure for this, so there is a growing need for standardization for safe decommissioning. Therefore, I will briefly review the activation assessment methods and procedures that should be given priority when ecommissioning various types of cyclotron facilities. In this study, I examined the general decommissioning procedures related to the radioactivity assessment that must precede a cyclotron facility producing PET radiotracers (C11, N13, O15, F18) used in medical institutions in Korea, and presented four methods to evaluate the radioactivity level: Monte Carlo computer simulation, γ spectroscopy, neutron fluence estimation by sampling, and profile analysis using concrete boring. In addition, I presented a radiation measurement method and procedure using a conversion factor as a general method to grasp the overall radioactivity status of a cyclotron prior to establishing a decommissioning plan.