基于3DCBCT/4DCBCT保乳术后VMAT摆位误差测量与校正的比较研究

目的 探讨保乳术后自由呼吸状态下基于3DCBCT和4DCBCT测定的乳腺VMAT摆位误差间及摆位残差间差异。方法 选择保乳术后外照射患者20例,全部行4DCT扫描并勾画靶区,应用MONACO v5.10计划系统制定WMAT计划。分次治疗前隔次采集4DCBCT和3DCBCT图像各5次,将CBCT图像与计划CT图像配准,实施在线校正后再次采集CBCT图像,比较两种测量方法间摆位误差和摆位残差的差异。摆位误差和摆位残差间两两比较行配对t检验。结果 校正前基于4DCBCT测得的三维方向摆位误差均显著大于基于3DCBCT测得值(P=0.035、0.018、0.040)。校正后左右和前后方向基于3DCBCT获取的随机误差更小(0.5±0.39) mm∶(0.7±0.30) mm,P=0.005;(0.9±1.09) mm∶(1.2±0.48) mm,P=0.000]),前后方向基于3DCBCT获取的总摆位残差更小(0.2±0.33) mm∶(0.6±0.63) mm,P=0.000]。校正前后在前后方向基于4DCBCT测量值计算的摆位边界显著大于基于3DCBCT获得的(P=0.002)。结论 相对于3DCBCT,在三维方向上4DCBCT监测摆位误差的能力更强;两种方式在校正随机误差方面的效能相似,通过校正均能达到较为满意的体位重复度并缩小靶区外扩边界。

Comparison of 3DCBCT and 4DCBCT matching results in setup error assessment and correction for breast irradiation after breast-conserving surgery

Objective To compare the differences in setup error ( SE) assessment and correction between three-dimensional cone-beam computed tomography ( 3DCBCT ) and four-dimensional CBCT ( 4 DCBCT ) in breast irradiation patients during free breathing after breast-conserving surgery . Methods Twenty patients with breast cancer after breast-conserving surgery were recruited for external beam breast irradiation and 4DCBCT and 3DCBCT simulation. The target volumes were delineated. Volumetric modulated arc therapy plans were designed using the MONACO v510 treatment planning system. 3DCBCT and 4DCBCT images were collected alternately five times each before breast irradiation. The CT images were matched, and the interfraction SEs were acquired. After online setup correction, the residual errors were calculated, and the SEs, systematic errors, and random errors were compared. The paired t test was used for comparison between groups. Results The SEs acquired by 4DCBCT were significantly larger than those acquired by 3DCBCT in three directions ( P=0035, 0018, 0040 ) . After online setup correction, the random errors based on 3DCBCT were significantly smaller than those based on 4DCBCT in left-right and anterior-posterior ( AP ) directions ( 0.5± 039 mm vs. 0.7± 030 mm, P=0005;0.9± 109 mm vs. 1.2± 048 mm, P=0000) , and the residual errors based on 3DCBCT were also significantly smaller than those based on 4DCBCT in AP direction (0.2±033 mm vs. 0.6±063 mm, P=0000). The setup margins based on 4DCBCT was significantly larger than those based on 3DCBCT in AP direction both before and after online setup correction (P=0002). Conclusions Compared with 3DCBCT, 4DCBCT has more advantages in monitoring the SEs in three directions. Both 3DCBCT and 4DCBCT have similar efficacy in random error correction. The satisfying position repeatability and minimized target volume margins will be achieved by online setup correction.