Objective:To study the effect of the conjunction area in accelerator carbon fiber treatment couch on radio-therapy dosage.Methods:The dose of X-ray penetrating and avoiding the conjunction area in carbon fiber treatment couch were measured by using two-dimensional ionization chamber matrix (MatriXX).Effect of the conjunction area in carbon fi-ber treatment couch on X-ray dose of different gantry angles were analyzed.Gamma pass rates for ten VMAT radiotherapy plans with X-ray penetrating or avoiding the conjunction area were compared.Results:Great attenuation of X-ray could be observed when the X-ray penetrated the conjunction area in carbon fiber treatment couch especially with the gantry angle between 110°~180°.The attenuation range was between front 3cm and back 11cm at the extended boundaries of the treat-ment couch.When the gantry angle was between 116°~180°,the dose deviation of some measurement points exceeded 10%. At 145°gantry angle,the max deviation reached 24.2%.In the VMAT radiotherapy plans of ten real patients,the Gamma pass rate of X-ray penetrating the conjunction area in carbon fiber couch reduced significantly compared with that of X-ray avoiding the conjunction area (t=4.349,P =0.002).Conclusion:The conjunction area in accelerator carbon fiber treatment couch could reduce radiotherapy dosage significantly.The body position of radiotherapy should avoid the radiation fields penetrating the conjunction area in carbon fiber treatment couch.If it can't be avoided,ray attenuation caused by the conjunc-tion area should be considered in the design of radiotherapy plan.%目的：探讨加速器碳纤维治疗床结合部对调强放疗剂量的影响。方法：利用二维平板电离室矩阵，测量6MV X 射线穿射过碳纤维治疗床延长板结合部和避开结合部后的剂量。分析不同机架角度下治疗床结合部对 X 射线剂量的影响。比较实例放疗计划穿射与避开结合部的治疗计划的验证通过率。结果：二维矩阵电离室实测结果显示，射野处于110°～180°机架角范围，穿射结合部位后射线会产生较大衰减，结合部衰减范围集中在延长板分界向床头方向3cm，床尾方向11cm 的范围。116°～180°机架角，部分测量点剂量偏差值超过10％。145°机架角时测量点最大偏差值达24．2％。10例实例测量 VMAT 治疗计划中，射野穿透结合部的 Gamma 通过率较避开结合部显著降低（t ＝4．349，P ＝0．002）。结论：加速器碳纤维治疗床延长板结合部可显著降低放疗剂量。在放射治疗摆位应尽可能避免治疗射野穿射碳纤维治疗床结合部，无法避免时，应将其产生的射线衰减考虑在治疗计划的设计中。
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