Radioactivation Investigation for Concrete in Synchrotron-Type Proton Therapy Facilities

다국어 초록 (Multilingual Abstract)

Background: This study aimed to investigate the activation characteristics of concrete in synchrotron-type proton therapy facilities for future decommissioning. The larger synchrotron-type proton therapy facilities have a greater potential impact on decontamination than the cyclotron proton therapy facilities investigated in our previous study. Specific activity levels in the concrete after 30 years of operation in synchrotron-type proton therapy facilities were predicted from the measured thermal neutron fluence rates on the concrete during the operation to compare them with the clearance level. Materials and Methods: The investigations were conducted in the synchrotron-type proton therapy facilities at Medipolis Proton Therapy Research Center and Proton Medical Research Center, University of Tsukuba Hospital. The thermal neutron fluence rates on the concrete during the operation were measured by three different methods: using 24Na radioactivity produced in concrete, thermoluminescence dosimeters, and Au foils. Results and Discussion: The specific activity levels in the concrete throughout the synchrotron proton therapy facilities were negligible compared with the clearance level. The specific activity level of concrete in the accelerator room in synchrotron-type proton therapy facilities where an accelerator controls the proton energy was much lower than that in cyclotron-type proton therapy facilities where a degrader controls the proton energy. Conclusion: Concrete does not need to be treated as radioactive waste when decommissioning synchrotron-type proton therapy facilities.