医学放射工作人员眼晶体剂量计校准方法研究

Eye lens is very sensitive to ionizing radiation. Excessive radiation exposure can cause lens opacities, cataract and even blindness. Based on lots of epidemiological studies, ICRP and IAEA have recommended that the threshold value for the absorbed dose to the eye lens is 0.5 Gy and the annual dose limit for the eye lens should be reduced to 20 mSv. The monitoring for the eye lens doses of occupational works is strongly recommended. Nowadays, the eye lens dosemeter especially dedicated to measurements of Hp(3) have been developed in the worldwide and the studies about calibration methods of eye lens dosemeters are ongoing. However, these calibrations cannot be proceeded in China. This project proposes to establish the conversion coefficient standard database by Monter Carlo simulations, calculations and verfications of the conversion coefficient Hp(3)/Kair of three phantoms under the conditions of various incident angles, different photon monoenergies and radiation qualities of X/γ reference radiation. Furthermore, this project also focuses on establishing the backscatter factor standard database and gaining the abilities of eye lens dosemeters calibration by simulations and experiments of the backscatter factor of three phantoms under the conditions of various incident angles and different radiation qualities of X/γ reference radiation. Finally, in order to provide protections for medical radiation workers, a secondary standard equipment used to calibrate eye lens dosemeter will be designed according to X/γ radiation fields in medical applications.

眼晶体对电离辐射非常敏感，过量的辐射照射会引起眼晶状体混浊、白内障甚至失明。对流行病学研究证据评议后，ICRP和IAEA认为眼晶体吸收剂量阈值为0.5 Gy，眼晶体年当量剂量限值降低至20 mSv，必须对放射工作人员眼晶体剂量进行监测。国际上已研制了专用于测量眼晶体剂量Hp(3)的剂量计，正在开展眼晶体剂量计校准方法研究，国内尚不能对眼晶体剂量计进行校准。本项目通过Monte Carlo程序模拟计算并验证不同入射角度与不同单能光子辐射、X/γ参考辐射的不同辐射质照射条件下，三种模体的Hp(3)/Kair转换系数，建立转换系数标准数据库。通过模拟计算和实验验证不同入射角度与不同辐射质照射条件下，三种模体的反散射因子，建立反散射因子标准数据库，建立眼晶体剂量计校准参考辐射场，具备校准能力。根据医用X/γ辐射场特点，设计用于校准眼晶体剂量计的次级标准仪器，为医学放射工作人员的健康提供保障。

眼晶体对电离辐射非常敏感，ICRP和IAEA建议眼晶体年当量剂量限值降低至20 mSv，国际上正在开展眼晶体剂量计校准方法研究。本项目基于Geant4程序实现了眼晶体剂量当量Hp(3)、比释动能K、相对偏差R的模拟计算、建立了不同入射角度与不同单能光子辐射、X/γ参考辐射的不同辐射质照射条件下，三种模体的转换系数Hp(3)/Kair标准数据库，设计并制作了三种模体的实物水体模，根据模拟计算和实验测量，建立了三种模体的反散射因子标准数据库，中国辐射防护研究院现已具备X/γ参考辐射场中眼晶体剂量计的校准能力。初步设计了直接测量眼晶体剂量当量Hp(3)、可校准眼晶体剂量计的次级标准电离室，可为医学放射工作人员的健康提供保障。