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在中国计量科学研究院医用加速器实验室,用自制的三维水箱测量系统对水吸收剂量绝对测量条件下的光子辐射场的剂量学参数开展了研究。基于这套三维水箱测量系统测量了加速器机架90°、源皮距SSD=1 000 mm、辐射野面积100 mm×100 mm实验条件下的6 MV光子辐射野均整曲线及百分剂量分布曲线,通过与常规商用三维水箱测量系统的相应测量结果进行对比后发现,本工作的研究方案基本可行。结合开展加速器光子水吸收剂量绝对测量研究的具体需求,从6 MV光子辐射野均整曲线中分析得出了水下深度100 mm处,直径60 mm范围内INLINE方向的均整性和对称性分别为100.5%、100.1%,CROSSLINE方向均整性和对称性分别为101.1%、101.4%,满足开展光子水吸收剂量测量的基本条件。
The dosimetry parameters of photon radiation field under the condition of absolute measurement of absorbed dose of water were studied in the medical accelerator laboratory of China National Institute of Metrology with a homemade three-dimensional water tank measuring system. Based on the three-dimensional water tank measurement system, the 6 MV photon emission field average curve and the percentage dose distribution curve of accelerator frame at 90 °, source skin distance SSD = 1 000 mm and radiation field area 100 mm × 100 mm were measured. By comparing with the corresponding measurement results of conventional commercial three-dimensional water tank measuring system, it is found that the research scheme of this work is basically feasible. According to the specific requirements of absolute measurement of absorbed dose of accelerator photon water, the average and symmetry of INLINE direction at 100 mm underwater depth and 60 mm diameter were analyzed respectively from the average curvature curve of 6 MV photon radiation, and they were 100.5 %, 100.1%. The homogeneity and symmetry of CROSSLINE direction were 101.1% and 101.4%, respectively, which satisfied the basic conditions for measuring the absorbed dose of photon water.