Li Winnie, Moseley Douglas J, Bissonnette Jean-Pierre, Purdie Thomas G, Bezjak Andrea, Jaffray David A
Princess Margaret Hospital, University of Toronto, Ontario, Canada.
Med Dosim. 2010 Winter;35(4):287-96. doi: 10.1016/j.meddos.2009.09.003. Epub 2009 Oct 29.
We report the setup reproducibility of thoracic and upper gastrointestinal (UGI) radiotherapy (RT) patients for 2 immobilization methods evaluated through cone-beam computed tomography (CBCT) image guidance, and present planning target volume (PTV) margin calculations made on the basis of these observations. Daily CBCT images from 65 patients immobilized in a chestboard (CB) or evacuated cushion (EC) were registered to the planning CT using automatic bony anatomy registration. The standardized region-of-interest for matching was focused around vertebral bodies adjacent to tumor location. Discrepancies >3 mm between the CBCT and CT datasets were corrected before initiation of RT and verified with a second CBCT to assess residual error (usually taken after 90 s of the initial CBCT). Positional data were analyzed to evaluate the magnitude and frequencies of setup errors before and after correction. The setup distributions were slightly different for the CB (797 scans) and EC (757 scans) methods, and the probability of adjustment at a 3-mm action threshold was not significantly different (p = 0.47). Setup displacements >10 mm in any direction were observed in 10% of CB fractions and 16% of EC fractions (p = 0.0008). Residual error distributions after CBCT guidance were equivalent regardless of immobilization method. Using a published formula, the PTV margins for the CB were L/R, 3.3 mm; S/I, 3.5 mm; and A/P, 4.6 mm), and for EC they were L/R, 3.7 mm; S/I, 3.3 mm; and A/P, 4.6 mm. In the absence of image guidance, the CB slightly outperformed the EC in precision. CBCT allows reduction to a single immobilization system that can be chosen for efficiency, logistics, and cost. Image guidance allows for increased geometric precision and accuracy and supports a corresponding reduction in PTV margin.
我们报告了通过锥形束计算机断层扫描（CBCT）图像引导评估的两种固定方法用于胸部和上消化道（UGI）放疗（RT）患者时的设置重复性，并基于这些观察结果给出了计划靶区（PTV）边界的计算。对65例采用胸板（CB）或抽空垫（EC）固定的患者的每日CBCT图像，使用自动骨性解剖配准法与计划CT进行配准。匹配的标准化感兴趣区域集中在肿瘤位置附近的椎体周围。在放疗开始前校正CBCT和CT数据集之间>3 mm的差异，并用第二次CBCT进行验证以评估残余误差（通常在初始CBCT 90秒后进行）。分析位置数据以评估校正前后设置误差的大小和频率。CB（797次扫描）和EC（757次扫描）方法的设置分布略有不同，在3 mm行动阈值处的调整概率无显著差异（p = 0.47）。在10%的CB分次和16%的EC分次中观察到在任何方向上设置位移>10 mm（p = 0.0008）。无论固定方法如何，CBCT引导后的残余误差分布是等效的。使用已发表的公式，CB的PTV边界为：左右方向（L/R）3.3 mm；前后方向（S/I）3.5 mm；上下方向（A/P）4.6 mm，EC的PTV边界为：L/R 3.7 mm；S/I 3.3 mm；A/P 4.6 mm。在没有图像引导的情况下，CB在精度上略优于EC。CBCT允许简化为单一的固定系统，可根据效率、后勤和成本进行选择。图像引导可提高几何精度和准确性，并支持相应减小PTV边界。
