Abstract: 【Abstract】 Objective To measure the setup-error in the intensity modulated radiation therapy after breast-conserving operation using the Thorawedge breast bracket. Methods Patients of 10 cases were applied with the Thorawedge breast bracket for positioning and intensity modulated radiation therapy after breast-conserving operation. Technicians set up with the setup signs and screened using the electronic portal imaging device (EPID), and the error was analyzed through comparing the portal film with the digitally reconstructed radiographs (DRR) in the MOSAIQ system. Result The setup errors were (3.29±1.58）mm in left-right direction,（2.38±1.36）mm in cranial-caudal direction,（3.51±3.05）mm in anterior-posterior direction. The percentage of the setup errors exceed 5mm were 18.8％，12.5％，31.3％in three directions. Conclusion There exists some extent of setup error in the intensity modulated radiation therapy after breast-conserving operation using the Thorawedge breast bracket. We can use EPID on-line to correct the setup error in order to improve the setup precision.

摘要： 目的 研究乳腺癌保乳术后调强放疗患者使用Thorawedge乳腺托架作体位固定的临床摆位误差。方法 选取10例在我院进行乳腺癌保乳术后调强放疗患者，均使用Thorawedge乳腺托架作体位固定的，每天技术员根据患者体表标记线完成摆位后，使用电子射野影像系统（Electronic Portal Imaging Device ，EPID）进行拍片，拍摄正侧位片共100幅图像，所获得的图像在MOSAIQ系统利用Image Review与治疗计划标准射野数字重建（Digitally Reconstructed Radiograph ，DRR）图像进行比较，测出患者在左右、头脚、前后三个方向的摆位误差。结果 该10例患者的摆位误差在左右方向、头脚方向和前后方向平均摆位误差分别为：3.29±1.58mm，2.38±1.36mm，3.51±3.05mm，三个方向上摆位误差大于5mm 的百分率分别为18.8％，12.5％，31.3％。结论 在乳腺癌保乳术后调强放疗使用Thorawedge乳腺托架，摆位时应使用EPID系统进行实时摆位误差纠正，提高摆位精度。

关键词: 乳腺癌, 调强放疗, 乳腺托架, 摆位误差, Breast Cancer, IMRT, Breast Bracket, Setup Error