Abstract: Objective　To explore the correlation and difference of the lower neck and lower vertebral body of nasopharyngeal carcinoma in the same direction, to provide the basis for improving the accuracy of neck positioning, and to provide ideas for improving the head-neck-shoulder fixation device. Methods　A total of 80 patients with nasopharyngeal carcinoma who received Varian Vital Beam linac radiation therapy were randomly selected in Sun Yat-sen University Cancer Prevention and Treatment Center from January to December 2021, and their 1 120 cone beam CT (CBCT) images were retrospectively analyzed. The correlations and differences of two different matching regions in the linear translation directions of left-right (LR), head-foot (SI), and anterior-posterior (AP) and in the axial rotation directions of transverse rotation Roll, sagittal rotation Pitch, coronal rotation RTN were analyzed. Pearson correlation analysis was used for the correlation analysis, Wilcoxon signed rank test or paired sample t test was used for the measurement data. Results　In the linear translation directions of the lower neck and lower vertebral body, there was a moderate correlation in the LR direction (r=0.692, P<0.001), and there was no statistically significant difference (P>0.05); there was a moderate correlation in the SI direction (r=0.623, P<0.001), and there was a statistically significant difference (t=-2.967, P=0.003); there was a strong correlation in the AP direction (r=0.894, P<0.001), and there was a statistically significant difference (t=-5.965, P<0.001). In the axial rotation directions of the lower neck and lower vertebral body, there was a moderate correlation in the sagittal rotation Pitch direction (r=0.655, P<0.001), and there was a statistically significant difference (t=5.228, P<0.001); there was a moderate correlation in the coronal rotation RTN direction (r=0.594, P<0.001), and there was no statistically significant difference (P>0.05); there was a strong correlation in the transverse rotation Roll direction (r=0.758, P<0.001), and there was a statistically significant difference (Z=-2.985, P=0.003). Conclusions　The correlation of the lower neck and the lower vertebral body is strong, so the lower vertebral body can be used as the reference to correct the lower neck error, but the difference caused by rotation error should be paid attention to. It is suggested to pay attention to correcting and guiding the patients' lying posture when positioning, and ensure that the position is consistent with the mask, to reduce the rotation error of the neck.

Key words: Correlation and difference, Lower neck error, Image guidance, Linearity error and rotation error

摘要： 目的　探索鼻咽癌下颈部和下椎体的同方向的相关性与差异性，为提高颈部摆位精准度提供依据以及对改良头颈肩固定装置提供思路。方法　随机选取2021年1月至12月中山大学肿瘤防治中心80例接受Varian Vital Beam直线加速器放射治疗的鼻咽癌患者，回顾性分析1 120次锥形束CT（cone beam CT，CBCT）图像分别在两个不同匹配区域线性平移方向中左右LR、头脚SI、前后AP以及轴向旋转方向中横断旋转Roll、矢状旋转Pitch、冠状旋转RTN 6个方向摆位误差的同方向的相关性与差异性。相关性分析采用Pearson相关性分析；计量资料采用Wilcoxon带符号秩检验或配对样本t检验。结果　在线向平移方向下颈部与下椎体同方向上，左右LR存在中等相关（r=0.692，P<0.001），差异无统计学意义（P>0.05）；头脚SI存在中等相关（r=0.623，P<0.001），差异有统计学意义（t=-2.967，P=0.003）；前后AP存在强相关（r=0.894，P<0.001），差异有统计学意义（t=-5.965，P<0.001）。在轴向旋转方向下颈部与下椎体同方向上，矢状旋转Pitch存在中等相关（r=0.655，P<0.001），差异有统计学意义（t=5.228，P<0.001）；冠状旋转RTN存在中等相关（r=0.594，P<0.001），差异无统计学意义（P>0.05）；横断旋转Roll存在强相关（r=0.758，P<0.001），差异有统计学意义（Z=-2.985，P=0.003）。结论　下颈部和下椎体相关性较强，可以用下椎体为基准校正下颈部误差，但要注意旋转误差造成的差异性。建议摆位时注意纠正并指导患者平躺姿势，确保体位和面罩吻合度，减少颈部的旋转误差。

关键词: 相关性与差异性, 下颈部误差, 图像引导, 线性误差与旋转误差