Objective To establish a method using electronic portal imaging device(EPID)to acquire the setup errors and to calculate the margin of planning volume for neck and upper thoracic esophageal cancer in radiotherapy. Methods Twenty-five patients with neck and upper thoracic esophageal cancer were fixed by head-neck-shouder thermoplastic mask. Setup errors in X,Y and Z direction were calculated by comparing the position offset of the relevant osscous marks between DDR and EPI. According to the formulation,the size of MPTV with or without consideration of organ motion was calculated as well. Results The standard deviations of systematic errors(Σ)were 0.85mm,1.37mm and 0.94mm at X,Y and Z direction, respectively,The standard deviations of random errors(σ)were 0.95mm,0.74mm and 0.89mm at X,Y and Z direction, respectively,Without consideration of organ motion,the sizes of MPTV were 3.84mm,3.94mm and 2.97mm at X,Y and Z direction,respectively,with consideration of organ motion,the sizes of MPTV were 7.1mm,7.67mm and 7.19mm at X, Yand Z direction. Conclusion Through the retrospective analysis of the setup errors of twenty-five patients with neck and upper thoracic esophageal cancer,actually measuring the value of MPTV is more reasonable in planning the radiotherapy regime.%目的：用电子射野影像验证系统（EPID）测量分析颈、胸上段食管癌适形调强放疗的摆位误差，以制定合适的适形调强放疗计划。方法25例行适形调强放射治疗的颈、胸上段食管癌患者，制作头颈肩热塑膜，通过应用EPID比较计划射野参考图像（DRR）和实际射野验证图像（EPI）相关骨性标记的位置偏移，计算出三维方向的摆位误差，并由公式MPTV=2.5Σ+0.7σ分别计算出不考虑与考虑靶区内扩边的具体MPTV值。结果25例患者在X、Y、Z轴上的摆位系统误差标准差（Σ）分别为0.85mm、1.37mm、0.94mm，摆位随机误差标准差（σ）分别为0.95mm、0.74mm、0.89mm。不考虑靶区内扩边的MPTV值分别为3.84mm、3.94mm、2.97mm，考虑靶区内扩边的MPTV值的为7.1mm、7.67mm、7.19mm。结论通过回顾性分析25例颈、胸上段食管癌患者适形调强放疗的摆位误差，实测MPTV的大小，从而使制定适形调强放疗计划更具科学性。
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