Abstract: Objective To analyze and determine the shielding protection design project of a rebuilt accelerator radiotherapy room,and to estimate and verify the radiation level of the focus area outside the room,so as to provide experimental basis for the scientific design of radiation protection of therapy room. Methods From 2020 to 2023,A 10 MV accelerator and the treatment room to be rebuilt were used as the research objects,the shielding width of primary radiation beam and the dose rate of the attention points outside the accelerator room were estimated and detected by means of the calculation methods provided by IAEA 47,NCRP 151 and GBZ/T 201.2-2011 "Radiation shielding specification for radiation therapy room Part 2：Electronic linear accelerator radiation therapy room",etc. An X/γ dose rate meter typed 6150 AD b/H/ was used to verify the radiation level of attention area outside the machine room,and analyzed and the measurement data were evaluated according to relevant technical specifications and standards. Results A normal X-ray simaulating positioning machine room was transformed into an accelerator radiotherapy room with a maximum X-ray of 10 MV,and the shielding design of the accelerator radiotherapy room was determined. The dose rates from the primary radiation beam zone outside the south wall,the north wall and the roof of the room were 1.67,0.30 and 1.65 μSv/h,respectively. The theoretical calculated dose rates from the primary radiation beam zone outside the wall were almost consistent with the measured values,and the measured values in the second radiation beam zone outside the wall were all in the background radiation levels. The measured dose rate outside the protective door were all lower than 2.5 μSv/h,and the measured dose rate on the surface of the door body was about 4 times of the theoretical calculated value. Conclusion It is reasonable and feasible to change the area of simulating positioning machine into an accelerator treatment room,the shielding design of the protective door and its effect verification are the key points of radiation protection and appropriate measures should be taken to effectively reduce the radiation level outside the protective door.

Key words: Accelerator, Radiotherapy room, Protection design, Radiation protection