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目的:探讨宫颈癌患者体质量指数(BMI)对调强放疗摆位误差的影响，以及在不考虑旋转误差、靶区及邻近器官变化的情况下不同BMI宫颈癌患者放疗的最佳体位。方法:将90例宫颈癌患者根据BMI分为过轻组(BMI≤18.4 kg/mn 2)、正常组(18.5 kg/mn 2≤BMI≤23.9 kg/mn 2)和超重组(BMI≥24 kg/mn 2)，每组各30例。每组内又分为仰卧位(15例)和俯卧位(15例)两种体位固定方式。获取90例宫颈癌患者共2 250组CBCT数据，记录并分析每组内摆位误差大小，并根据公式Mn PTV＝2.5Σ＋0.7σ计算最佳体位靶区外扩边界值。n 结果:不考虑BMI分组情况下，仰卧位和俯卧位在n x、n y、n z轴向的摆位误差差异均无统计学意义(n P>0.05)。考虑BMI情况下，过轻组中仰卧位在n x、n y轴向的摆位误差小于俯卧位(n P0.05)，其对应的仰卧位Mn PTV为4.76、4.27、5.73 mm；正常组中仰卧位和俯卧位n x、n y轴向的摆位误差差异无统计学意义(n P>0.05)，但n z轴向的摆位误差俯卧位小于仰卧位，其对应的俯卧位Mn PTV为6.42、10.21、4.91 mm；超重组中仰卧位和俯卧位在x、n z轴向的摆位误差差异无统计学意义(n P>0.05)，但n y轴向的摆位误差俯卧位小于仰卧位，其对应的俯卧位Mn PTV为5.88、5.26、5.32 mm。n 结论:不考虑旋转误差、靶区及邻近器官变化情况下，BMI≤18.4时固定方式选择仰卧位较好，BMI≥18.5时固定方式选择俯卧位较合适。“,”Objective:To investigate the effect of body mass index (BMI) on setup errors in intensity-modulated radiotherapy for cervical cancer and explore the optimal position for patients with different BMI without taking into account the rotation error and the changes in target area and adjacent organs.Methods:A total of 90 patients were divided into three groups according to their BMI: light weight group (BMI≤18.4 kg/mn 2), normal weight group (18.5 kg/mn 2≤BMI≤23.9 kg/mn 2) and overweight group (BMI≥24 kg/mn 2). Thirty patients were assigned into each group including15 patients in the supine position and 15 patients in the prone position. In total, 2 250 sets of CBCT scan data of 90 patients were obtained. The setup errors were recorded and analyzed in each group. The margins of the optimal position were calculated according to the formula of Mn PTV=2.5+ 0.7.n Results:When BMI was not taken into account, there was no significant difference in the setup errors between the supine and prone positions in the x, y and z directions (all n P>0.05). When BMI was considered, the setup error in the supine position were significantly smaller than those in the prone position in the x and y directions in the light weight group, whereas there was no significant difference in the setup errors between the supine and prone positions in the z direction (n P>0.05). The corresponding Mn PTV in the supine position was 4.76, 4.27 and 5.73 mm, respectively. In the normal weight group, there was no significant difference in the setup errors between the supine and prone positions in the x and y directions (both n P>0.05), whereas the setup error in the prone position was smaller than that in the supine position in the z direction. The corresponding Mn PTV in the prone position were 6.42, 10.21 and 4.91 mm, respectively. In the overweight group, there was no significant difference in the setup errors between the supine and prone positions in the x and z directions (all n P>0.05), whereas the setup error in the prone position was smaller than that in the supine position in the y direction. The corresponding Mn PTV in the prone position were 5.88, 5.26 and 5.32 mm, respectively.n Conclusions:Without taking into account the rotation error and the changes in target area and adjacent organs, when the BMI≤18.4, the supine position is recommended. When the BMI≥18.5, it is better to choose the prone position.