自由呼吸状态下X线平片和CBCT在EB-PBI摆位误差测定与校正的比较研究

Comparison of orthogonal kilovolt X-ray images and cone-beam CT matching results in setup error assessment and correction for EB-PBI during free breathing

目的 对比研究EB-PBI患者自由呼吸状态下正交X线平片和CBCT测得的摆位误差、摆位残差的差异.方法 选择保乳术后EB-PBI患者19例,基于校正前后CBCT图像、正交X线平片分别获取三维方向摆位误差及校正后摆位残差.Wilcoxon符号秩和检验两种方法差异.结果 CBCT、正交X线平片的分次间摆位误差的系统误差仅前后方向不同（-1.2、2.0 mm,P=0.005）,随机误差在三维方向均相近（P=0.948、0.376、0.314）.与正交X线平片相比CBCT降低了前后方向摆位残差（系统误差-0.2、0.5 mm,P=0.008,随机误差0.5、1.3 mm,P=0.002）.校正前后CBCT的摆位误差在前后方向均明显小于X线平片（系统误差-1.4、5.6 mm,P=0.003,随机误差0.0、3.2mm,P=0.003）.结论 与CBCT相比,正交X线平片增加了发现前后方向摆位误差的能力,但CBCT的摆位残差降低更明显.对EB-PBI患者X线平片获取时间短、辐射量低且摆位验证精度可信,适用于IGRT或摆位误差分析.

Objective To compare the differences in setup error （SE） assessment and correction between the orthogonal kilovolt X-ray images and CBCT in EB-PBI patients during free breathing. Methods Nineteen patients after breast conserving surgery EB-PBI were recruited. Interfraction SE was acquired using orthogonal kilovolt X-ray setup images and CBCT, after on-line setup correction, calculate the residual error and compare the SE, residual error and setup margin （SM） quantified for orthogonal kilovolt X-ray images and CBCT. Wilcoxon sign-rank test was used to evaluate the differences. Results The CBCT based SE （systematic error, Y~） was smaller than the orthogonal kilovolt X-ray images based E in AP direction （ -1.2 mm vs 2. 00 mm; P = 0. 005 ）, and there was no statistically significant differences for three dimensional directions in random error （cr） （ P = 0. 948,0. 376,0. 314 ）. After on-line setup correction, CBCT decreases setup residual error than the orthogonal kilovolt X-ray imagesin AP direction （ E ： - 0. 20 mm vs 0. 50 mm, P = 0. 008 ; cr ： 0.45 mm vs 1.34 mm, P = 0. 002 ）. And also the CBCT based SM was smaller than orthogonal kilovolt X-ray images based SM in AP direction （ E ： - 1.39 mm vs 5.57 mm, P = 0. 003 ;cr ：0. 00 mm vs 3.2 mm, P = 0. 003 ）. Conclusions Compared with kilovolt X-ray images, CBCT underestimate the setup error in the AP direction, but decreases setup residual error significantly. An image- guided radiotherapy and setup error assessment using kilovolt X-ray images for EB-PBI plans was feasible.