Bunker shielding design scheme for low energy medical linear accelerator: Comparison between Chinese and international radiation shielding standards for radiotherapy facilities

Objective: To calculate and compare the three shielding schemes for a low energy medical linear accelerator according to different Chinese and foreign radiation shielding standards, with a view to provide reference for revising and improving the Chinese national standards. Methods: For a regular bunker with 6 MV X-ray linear accelerator to treat an average of 125 patients (90% with IMRT technology) per day, the corresponding shielding schemes are calculated according to NCRP report 151 (America), IRR 17 legislation (British) and Chinese national standard GBZ/T 201, respectively. The concrete shielding thickness required for the points of concern, and their influence on the indoor usable area, the indoor floor height, and the roof load-bearing in each scheme were evaluated and compared. Results: The values of concrete shielding thickness required for points A and B (secondary barrier of the primary wall), C and D (primary barrier of the primary wall), E (secondary barrier of the side wall), F (primary barrier of the roof) and G (secondary barrier of the roof) according to NCRP 151 report and IRR 17 legislation were 79, 105, 136, 166, 104, 137, 76 cm and 94, 126, 183, 189, 119, 175, 92 cm, respectively. The values of concrete shielding thickness according to the Chinese national standard GBZ/T 201 for these points were 117, 133, 207, 227, 121, 175, 94 cm, respectively, significantly higher than the foreign values, especially about the primary beam. At the same time, GBZ/T standard were significantly decreased the indoor usable area and floor height of the treatment room were 11.24% and 7.13%, respectively, less than those calculated under NCRP report 115, especially with the roof load-bearing increased by 25.20%. Conclusions: GBZ/T achieved the thickest shielding requirement, especially, the primary shielding were significantly increased according to the instantaneous dose rate limit required by the current national standard. (authors)