目的:探讨和比较瓦里安(Varian)2100C/D与医科达(Elekta) Synergy直线加速器配备的多叶准直器的半影特性,为临床设野提供参数供参考.方法:利用CRS 三维水箱和PTW电离室测量6MV和10MVX线的射野离轴比曲线,测量从4 cm×4 cm到20 cm×20 cm各方野的半影;同时针对两种加速器多叶准直器的设计特点,分析利用不同准直器形成射野对半影宽度的影响.结果:(1)对于不同能量和不同大小射野,设野时靶区外扩的范围应综合半影大小等因素;(2) Varian 2100C/D加速器采用准直器三层结构,采用“MLC+JAW”方式形成射野能减少半影,即应注意形成射野时JAW必须跟随MLC; (3) Elekta Synergy加速器形成射野时MLC方向半影较大,重要器官可采用JAW来保护.%Objective: To evaluate the penumbra characteristic of the multi-leaf collimator in the Varian 2100C/D and Elekta Synergy linear accelerator, the result can be used as clinical reference. Methods: The penumbra was derived from beam profiles measured in water using PTW ion chamber with CRS water phantom. The penumbra width was measured for field sizes from 4x4 cm2, to 20x20 cm2.According to different features of collimators, variations of penumbra were investigated for different kinds of field-defining methods. Results: (1) Field margins (distance between field edge and the PTV outline) should be set according to both X-ray energy and field size (2) The MLC system in Varian linear accelerator is used as a tertiary collimator, 'MLC+ Jaw' fields should be used for field-defining. (3) The penumbra width is bigger in 'MLC 'dimension than that in 'Jaw' dimension for Elekta Synergy accelerator, organ at risk can be better shielded by JAW.
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