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目的:分析对比医用直线加速器中心轴光子绝对剂量输出的长期稳定性特点。方法:选取3台Varian加速器,以最新IAEA TRS-398报告中推荐的水中直接剂量法监测15个月内的剂量输出,用SPSS和Sigma Plot软件进行统计分析。结果:在390条数据中,超过±2%允差有7次(1.79%)。偏差主要分布在-0.2%~1.2%,最大+2.55%。同一加速器均整模式下不同能量输出稳定性差异显著(P<0.05),但无临床意义(<1 c Gy量级)。不同加速器的均整模式输出稳定性显著依赖于机龄(P<0.05),与机型无关,而非均整模式(FFF)间差异不显著。结论:包括较新的True Beam FFF模式在内的Varian加速器中心轴绝对剂量输出的长期稳定性良好,错误率为1%~2%。放疗中心可以晨检仪和标准水箱测量相结合的方法,监测并及时纠正该偏差。
Objective: To analyze and compare the long-term stability of photon absolute dose output in the central axis of a medical linear accelerator. METHODS: Three Varian accelerators were selected to monitor the 15-month dose output using the in-water direct dose method recommended in the latest IAEA TRS-398 report. Statistical analyzes were performed using SPSS and Sigma Plot software. Results: Of the 390 data, over ± 2% tolerances were seven (1.79%). Deviations are mainly distributed in -0.2% ~ 1.2%, maximum + 2.55%. There was significant difference (P <0.05) in the stability of different energy outputs in the same accelerator mode but no clinical significance (<1 c Gy). The output stability of the homogenous model with different accelerators depends significantly on the age (P <0.05), but not on the model, but not on the non-uniform mode (FFF). Conclusion: The long-term stability of the absolute dose output of the Varian accelerator central axis, including the newer True Beam FFF modes, is good with an error rate of 1% -2%. The radiotherapy center can monitor and correct the deviation in time by combining the morning gage with the standard water tank measurement.