As novel radiation therapy method,proton FLASH therapy can protect healthy organs surrounding tumor targets and improve treatment efficiency.However,the ultra-high dose rate of the proton beam during the patient treatment process may become a potential risk to radiation safety.It is necessary to evaluate the radiation safety under the proton FLASH treatment conditions before conducting clinical studies.In this study,a gantry treatment room of the superconducting cyclotron proton therapy system was selected for the investigation.And both transmission proton FLASH therapy and Bragg peak proton FLASH therapy scenarios were set up in the treatment room.According to the layout of the treatment room and the directions of the proton beams,a number of interested areas outside the radiation shielding were selected for the radiation measurement.Considering the short irradiation time and the ultra-high dose rate of proton FLASH therapy is not appropriate for ideal radiation measurement conditions,in this study the proton beam intensity was adjusted and the irradiation time was extended.Two radiation detectors were used to perform neutron and X/γ dose rates measurements at all interested areas.During the study,the linear relationship between the ambient dose-equivalent rate and the proton beam intensity was explored and verified,and the assessment of annual effective dose for all interested areas based on the actual measurements of the neutron and X/γ dose rates under different clinical FLASH irradiation conditions was carried out.The results indicated that the cumulative effective dose to the staff members outside the shielding layers is acceptable for the FLASH treatment in the gantry treatment room with controllable delivery time of ultra-high dose rate proton beam.
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