Measurement and analysis on distribution of radiation field dose inside the treatment room of TaiChi Pro multimodal integrated digital radiotherapy system

Objective:To examine the leakage radiation dose from the accelerator module's primary beam self-shielding,as well as stray radiation levels and distribution in the treatment room across various planes for the innovative X/γmultimodal radiotherapy system,TaiChi Pro,which is the world's first digitally integrated system that combines a linear accelerator,multi-source rotational focused gamma knife,and multi-modal image guidance,in order to formulate treatment room safety strategies and estimate additional radiation doses to patients. Methods:The TaiChi Pro multi-mode integrated radiotherapy system was utilized with a 6 MV X-ray accelerator in the flatten-filter free(FFF)treatment mode.The system has a primary radiation beam self-shielding,and an isocenter dose rate of 800 cGy/min.For detection points in various planes,an x,y,z coordinate system was established with the isocenter as the origin.To simulate the situation of patient,water-equivalent phantom was employed.The ambient dose equivalent and ambient dose equivalent rate at detection points in the radiation field were measured using thermoluminescence dosimeters. Results:The self-shielding area achieved a maximum dose of 114.0 mGy at 1 m distance from the target point after 3 min of cumulative irradiation.The leakage radiation ratios at all points remained below 0.5％,fulfilling the self-shielding design requirements.Regarding the couch,the highest radiation was observed in the opposite direction of the beam at the target point.The stray radiation on the treatment bed plane resulted in an ambient dose equivalent that did not exceed 0.5％of the ambient dose equivalent at the central point. Conclusion:The levels and distribution patterns of stray and leakage radiation inside the TaiChi Pro treatment room meet the requirements of the relevant national standard.The measured values of indoor radiation levels and distribution are very useful for room shielding design and personnel protection.