基于Halcyon加速器研究乳腺托架倾角对于保乳术后放疗摆位误差的影响

目的比较乳腺癌保乳术后患者采用不同乳腺托架俯仰角度的摆位误差,根据误差结果分别计算靶区各向外放值,为选择最适托架俯仰角提供依据。方法选取2019年12月至2020年4月,使用瓦里安Halcyon加速器治疗的乳腺癌保乳术后患者24例,所有患者均使用乳腺托架固定,根据托架俯仰角度随机分为0°组12例(A组)和7.5°组12例(B组)。患者每次治疗前均行MV-CBCT扫描,并与计划CT图像的刚性配准,获得患者三个方向的摆位误差,采用SPSS18.0软件分析两组数据是否存在统计学差异,采用独立样本t检验或用秩检验,以P<0.05作为差异有统计学意义。根据Margin公式分别计算两组CTV-PTV外扩距离。结果A、B两组三个维度摆位误差取绝对值后均值±标准差依次为:(0.28±0.24)cm、(0.31±0.28)cm(x);(0.37±0.26)cm、(0.53±0.34)cm(y);(0.38±0.31)cm、(0.46±0.35)cm(z);A、B两组三方向CTV-PTV外放距离分别为:0.49 cm和0.64 cm(x);0.55 cm和0.80 cm(y);0.52 cm和0.60 cm(z)。结论乳腺托架0°组三方向摆位误差均值全部小于7.5°组;临床工作中,建议在条件允许的情况下优先选择0倾斜角乳腺托架。此外,两种托架角度均出现较多奇异值的情况,表明对于乳腺癌保乳术后患者,采用Halcyon加速器每次治疗前的位置验证可显著提高治疗精度。

Study on the Effect of Breast Bracket Tilt Angle on Radiotherapy Setup Error after Breast Conserving Surgery Based on Halcyon Accelerator

Objective To compare the setup accuracy of different breast bracket angles after postoperative radiotherapy for breast cancer,so as to provide a reference for PTV projection.Methods A total of 24 breast cancer patients treated with Varian Halcyon accelerator from December 2019 to April 2020 were selected.All patients were fixed with breast brackets and randomly divided into group A(0°)and group B(7.5°)according to bracket Angle.All patients were matched with the CT images after MV-CBCT scan by rigid registration,and the setup errors of three orientations were obtained.Independent sample T-test or calibration T-test were performed according to whether the variance of the two groups of data was homogeneous.And calculating the CTV-PTV expansion distance of two groups.Results The mean±SD of group A and B in the three orientations of x,y and z were as follows:(0.28±0.24)cm,(0.31±0.28)cm;(0.37±0.26)cm,(0.53±0.34)cm;(0.38±0.31)cm,(0.46±0.35)cm.The variance of x and y directions was not homogeneous(P<0.05),and the corrected t-test was performed,while the independent sample t-test was performed in the z direction.The difference in y and z orientations was statistically significant(P<0.05).The CTV-PTV expansion distance of group A and B are 0.49 and 0.64 cm(x);0.55 and 0.80 cm(y);0.52 and 0.60 cm(z).Conclusion The mean setup errors of three orientations in the 0°group were less than that in the 7.5°group,and the 0°mode of the breast bracket had good repeatability.In clinical work,it is suggested that 0°brackets should be preferred if conditions permit.The use of both brackets presented more singular values,and the MV-CBCT verification before each treatment of Halcyon was of great value for postoperative radiotherapy of breast cancer patients.