Abstract: Objective　To analyze the error of simulated reduction verification in breast cancer patients before radiotherapy and to explore the necessity of simulated reduction verification before radiotherapy. Methods　One hundred and seventy-four breast cancer patients who received radiotherapy in Sun Yat-sen University Cancer Center from November 2020 to November 2021 were randomly selected for the retrospective study, with a total of 870 cone beam CT (CBCT) placement errors. The breast cancer patients who underwent X-ray simulation reduction verification before radiotherapy were set as group A; the breast cancer patients without simulated reduction verification were set as group B, and CBCT was used for postural verification during the treatment. The postural error data after CBCT calibration for the first treatment and the time required for the first treatment (the time in group A was the simulation reset verification time plus the first treatment time, and the time in group B was the first treatment time) were recorded and observed. The independent-sample t test analysis was conducted respectively. Results　The errors in the SI direction of the head and foot between group A and group B were (0.07±0.33) cm and (0.15±0.43) cm, with a statistical difference (t=3.575, P<0.001); there were no statistical differences in the left and right LR and anterior and posterior AP directions (both P>0.05). In the analysis of the first treatment time, the time of group A was much shorter than that of group B [(17.73±2.87) min vs. (34.51±3.28) min], with a statistical difference (t=48.480, P<0.001). According to the formula M_PTV=2.5∑+0.7σ, the external boundaries of group A and group B in all directions were calculated as below: LR 7.6 mm and 7.9 mm, SI 7.6 mm and 10.6 mm, and AP 10.2 mm and 10.7 mm. Conclusions　The repeatability of the patients in group A in the SI direction of the head and foot was better than that in group B after being verified by simulated reduction before radiotherapy; in the analysis of the first treatment time, the time of the patients in group A was much shorter than that in group B, and the time of the patients maintaining the treatment position was shortened. Reposition verification before upper breast cancer radiotherapy can improve the precision of radiotherapy and reduce the patients' positional uncertainty caused by a long single treatment time.

Key words: Simulation reset verification, CBCT, Breast cancer, Treatment time

摘要： 目的　分析乳腺癌患者放疗前有无模拟复位验证的误差并探讨放疗前模拟复位验证的必要性。方法　回顾性随机选择2020年11月至2021年11月在中山大学肿瘤防治中心接受放疗的乳腺癌患者174名（年龄20～60岁），共870次锥形束CT（cone beam CT，CBCT）摆位误差数据。把放疗前进行X线模拟复位验证的乳腺癌患者分为A组，无模拟复位验证的乳腺癌患者分为B组，治疗实施时使用CBCT进行体位验证。记录并观察首次治疗CBCT校准后的体位误差数据与首次治疗所需的时间（A组为模拟复位验证时间加首次治疗时间，B组为首次治疗时间），分别进行独立样本t检验分析。结果　A组与B组在头脚（SI）方向误差分别为（0.07±0.33）cm、（0.15±0.43）cm，两组比较差异有统计学意义（t=3.575，P<0.001）；而左右（LR）与前后（AP）方向比较，差异均无统计学意义（均P>0.05）。在首次治疗时间的分析中，A组时间远小于B组［（17.73±2.87）min比（34.51±3.28）min］，差异有统计学意义（t=48.480，P<0.001）。通过外放边界公式M_PTV=2.5∑+0.7σ计算出A组与B组在各个方向的外扩边界，A组与B组LR分别为7.6 mm、7.9 mm，SI分别为7.6 mm、10.6 mm，AP分别为10.2 mm、10.7 mm。结论　A组患者放疗前通过模拟复位验证后在SI方向重复性优于B组；在首次治疗时间的分析中，A组患者的时间远小于B组，患者治疗体位保持的时间缩短，在临床上乳腺癌放疗前进行复位验证可提高放疗的精确度，并且减少患者因单次治疗时间过长而引起的体位不确定性。

关键词: 模拟复位验证, CBCT, 乳腺癌, 治疗时间