摘要目的:比较使用头颈肩热塑网罩和颈胸一体热塑体膜固定的乳腺癌改良根治术后放疗患者锁骨上下区的摆位误差。方法:回顾性分析2019年6至12月中国医学科学院北京协和医学院肿瘤医院放疗科收治的40例女性乳腺癌改良根治术后患者[中位年龄46（29~68）岁]的锁骨上下区靶区的锥形束CT（CBCT）图像，其中19例使用头颈肩热塑网罩进行体位固定（头颈肩网罩组，128次CBCT图像），21例使用颈胸一体架膜进行体位固定（颈胸一体膜组，143次CBCT图像）。分析2组患者锁骨上下区的摆位误差，并分别测量肩锁关节的位置移动幅度 ΔX、 ΔY、 ΔZ和三维空间位移 d。应用公式计算临床靶区至计划靶区（PTV）的外放边界值。将所有患者分成体重指数（BMI）<24 kg/m 2组（13例，86次CBCT扫描）和BMI≥24 kg/m 2组（27例，185次CBCT扫描），分析比较2组的摆位误差。2组之间的比较采用独立样本 t检验。 结果:头颈肩网罩组和颈胸一体膜组在锁骨上下区的平移摆位误差分别为左右方向：（1.78±2.40） mm和（2.26±1.91） mm（ t=0.687， P=0.496）、头脚方向：（2.88±2.44） mm和（2.29±1.89） mm（ t=2.249， P=0.030）、腹背方向：（2.48±1.79） mm和（1.66±2.00） mm（ t=0.998， P=0.325）；在矢状面的旋转摆位误差分别为（0.91±0.61）度和（0.67±0.53）度，差异有统计学意义（ t=3.555， P=0.001）。头颈肩网罩组和颈胸一体膜组在肩锁关节的位置移动幅度 ΔX、 ΔY、 ΔZ的平均值分别为3.65、4.61、3.11 mm和2.32、1.97、1.63 mm，三维空间位移 d的平均值分别为7.36 mm和4.03 mm。头颈肩网罩组和颈胸一体膜组锁骨上下区在左右方向、头脚方向和腹背方向的PTV外放边界值分别为6.1、8.9、7.5 mm和7.0、7.0、5.5 mm。BMI<24 kg/m 2组和BMI≥24 kg/m 2组患者在3个方向的平移和旋转摆位误差的差异均无统计学意义（ t=-1.103~0.938，均 P>0.05）。 结论:对于乳腺癌改良根治术后行锁骨上下区放疗的患者，相比头颈肩网罩固定，使用颈胸一体膜固定在头脚方向的摆位误差更小，而且对肩锁关节的体位固定效果更优。

abstractsObjective:To compare the setup errors of breast cancer patients who received postmastectomy radiotherapy (PMRT) with head/neck and shoulder thermoplastic mask and integral cervicothoracic mask.Methods:A retrospective analysis was performed on 40 female breast cancer patients (median age 46 (29-68) years) who treated with PMRT in Cancer Hospital, Chinese Academy of Medical Sciences, Peking Union Medical College from June to December 2019. The supra/infraclavicular nodal region was irradiated with intensity-modulated radiotherapy technique and chest wall ± internal mammary chain were irradiated with electrons. A total of 271 cone beam CT (CBCT) images of the supra/infraclavicular nodal region were analyzed retrospectively. One hundred and twenty eight CBCT images were from 19 patients immobilized with head/neck and shoulder thermoplastic mask, and 143 CBCT images were from 21 patients immobilized with integral cervicothoracic thermoplastic mask. The setup errors of the two groups were analyzed, and the movement amplitude ΔX, ΔY, ΔZ and three-dimensional displacement d of acromioclavicular joint were measured. According to van Herk's formula, M PTV=2.5∑+0.7σ, the margin from clinical target volume to planning target volume (PTV) is calculated. According to whether body mass index (BMI)≥24 kg/m 2, the patients were divided into two groups to analyze whether there was statistical difference of the setup errors. The differences were compared by independent sample t test. Results:The translational setup errors of the supra/infraclavicular nodal region for head/neck and shoulder and integral cervicothoracic thermoplastic mask groups in the left-right, superior-inferior, and anterior-posterior directions were as follows: (1.78±2.40) mm and (2.26±1.91) mm ( t=0.687, P=0.496); (2.88±2.44) mm and 2.29±1.89 mm ( t=2.249, P=0.030); (2.48±1.79) mm and (1.66±2.00) mm ( t=0.998, P=0.325), respectively; the rotational setup errors in the sagittal directions were (0.91±0.61)° and (0.67±0.53)°, and the difference was statistically significant ( t=3.555, P=0.001). The arithmetic mean of movement amplitude of the acromioclavicular joint ( ΔX, ΔY, and ΔZ ) were 3.65, 4.61, 3.11 mm and 2.32, 1.97, 1.63 mm in the X, Y, and Z directions, respectively. The arithmetic mean of three-dimensional displacement dwere 7.36 mm and 4.03 mm, respectively. The calculated PTV margin in the left-right, superior-inferior, and anterior-posterior directions with head/neck and shoulder and integral cervicothoracic mask groups were 6.1, 8.9, and 7.5 mm and 7.0, 7.0, and 5.5 mm, respectively. No significant difference was found between the BMI<24 and BMI≥24 kg/m 2 groups in translation and rotation setup errors in the three directions ( t=-1.103 to 0.938, all P>0.05). Conclusions:The integral cervicothoracic mask system for patients who received PMRT in the supra/infraclavicular nodal region after the modified radical mastectomy provides smaller setup errors than the head and neck-shoulder thermoplastic mask system in the superior-inferior direction. This system also has remarkable body position fixation effects on the acromioclavicular region.