摘要 目的 研究Delta-4对MLC细小位置误差的探测敏感性。方法 利用瓦里安Trubeam型直线加速器配置EPID对MLC模拟细小位置偏差能力进行测量。设置2.0 cm (x)×6.0 cm (y)、7.0 cm (x)×6.0 cm (y)2个射野,MLC的x1、x2方向同时分别外扩0.1、0.2、0.3……0.9 mm和1.0、2.0……5.0 mm,使用3 mm 3%、2.5 mm2.5%、2 mm 2%、1.5 mm1.5%和1 mm1%标准γ分析。分析Delta-4测量的相对应剂量分布与TPS计算MLC位置不变时的剂量分布间差异。结果 Trubeam型直线加速器MLC具有移动丝米级位置能力。2.0 cm (x)×6.0 cm (y)射野2.5 mm2.5%标准下γ通过率100%,在MLC的x1、x2方向各打开0.3 mm时γ通过率下降至95.9%,打开0.5 mm时γ通过率下降至89.4%。7.0 cm (x)×6.0 cm (y)射野1.5 mm1.5%标准下γ通过率为96.5%,x1、x2方向各打开0.3 mm时γ通过率下降至95%以下,在打开3.0 mm内γ通过率都>90%。结论 适当提高γ分析标准有可能会改善Delta-4探测MLC位置细小偏差的敏感性,但不能对所有MLC丝米级位置误差探测出来。对不同大小射野,建议Delta-4选择不同分析标准。
Abstract：Objective To study the detective sensitivity for position of multi-leave collimators (MLC) using Delta-4. Methods First,the small positional deviation of MLC was simulated and measured using the linac (Varian,Trubeam) equipped with EPID.Then,two beam fields 2.0 cm (x)×6.0 cm (y),7.0 cm (x)×6.0 cm (y) were designed,the x1 and x2 of MLC were expanded 0.1 mm,0.2 mm,0.3 mm...0.9 mm and 1.0 mm,2.0...5.0 mm to external simultaneously,different parameters of 3 mm/3%,2.5 mm/2.5%,2 mm/2%,1.5 mm/1.5% and 1 mm/1% were used in Gamma analysis to analyze the difference between dose distribution detected by Delta-4 and original dose distribution with unexpanded MLC position derived from TPS. Results For 2.0 cm (x)×6.0 cm (y) beam field,the pass rate of original dose distribution was 100%,and that decreased to 95.5% when x1,x2 of MLC were expanded 0.3 mm to external,and decreased to 89.4% when expanded 0.5 mm at 2.5 mm/2.5% statistical standards. For 7.0 cm (x)×6.0 cm (y) beam field,the pass rate of original dose distribution was 96.5%,and that decreased to less than 95% when x2,x2 of MLC were expanded 0.3 mm to external,and passing rate was above 90% when MLC expanded less than 0.5 mm at 1.5 mm/1.5% statistical standards. Conclusions For MLC’s positional deviation in decimillimeter level,raise standards of Gamma analysis properly may improve the capability of Delta-4 for detecting small positional deviation,but it won’t detect all the positional deviation of MLC in decimillimeter level. For different size of beam field,it is proposed to use different analytical standards for Delta-4.
Ni Xinye,Gao Liugang,Lin Tao. Study of sensitivity for detecting small positional deviation of MLC by 3D Detector array Delta-4[J]. Chinese Journal of Radiation Oncology, 2016, 25(2): 168-171.
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