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目的：探索体部肿瘤放疗患者在模拟定位与放疗时床轴距变化对后野治疗深度的影响。方法将50例体部肿瘤放疗患者随机分成观察组与对照组，观察组患者在模拟定位及放疗时采用真空垫固定，对照组体部肿瘤患者仰卧于床板无其他固定装置。测量两组患者模拟定位及放疗时床轴距的数值及其差值变化，观察床轴距变化对体部肿瘤放疗患者后野治疗深度的影响。结果观察组在模拟定位与放疗时的床轴距差值较对照组小，两组床轴距差值的差异有统计学意义，<0.05。结论采用真空垫固定后放疗时，治疗床下沉程度更接近模拟定位时床板下沉度，床轴距变化对放疗时后野治疗深度影响减少，治疗更准确。“,”Objective To explore the ef ect of couch-to-isocentre distance change in simulation and radiotherapy for patients with body tumor on posterior beam depth.Methods 50 cases of patients with body tumor that treated in our department were randomly divided into two groups.The observation group used vacuum bag.The control group took supine position on the bed only.Analysed the change of couch-to-isocentre distance between the two grops when simulating and during the radiotherapy.Results The change of couch-to-isocentre distance when simulating and treating in observation group was not obvious when it was compared to control group. The dif erence between the two grops was statistical y significant.Conclusion The downward distance change of accelerater table and simulator bed in observation group is not obvious when treating with vacuum bag. The ef ect of couch-to-isocentre distance change on posterior beam depth is reduced and the radiotherapy accuracy is improved.