Purpose. The purpose of this work was to report on the geometric uncertainty for patients treated with multi-leaf collimator (MLC) tracking for lung SABR to verify the accuracy of the system. Methods. Seventeen patients were treated as part of the MLC tracking for lung SABR clinical trial using electromagnetic beacons implanted around the tumor acting as a surrogate for target motion. Sources of uncertainties evaluated in the study included the surrogate-target positional uncertainty, the beam-surrogate tracking uncertainty, the surrogate localization uncertainty, and the target delineation uncertainty. Probability density functions (PDFs) for each source of uncertainty were constructed for the cohort and each patient. The total PDFs was computed using a convolution approach. The 95% confidence interval (CI) was used to quantify these uncertainties. Results. For the cohort, the surrogate-target positional uncertainty 95% CIs were 2.5 mm (−2.0/3.0 mm) in left-right (LR), 3.0 mm (−1.6/4.5 mm) in superior–inferior (SI) and 2.0 mm (−1.8/2.1 mm) in anterior–posterior (AP). The beam-surrogate tracking uncertainty 95% CIs were 2.1 mm (−2.1/2.1 mm) in LR, 2.8 mm (−2.8/2.7 mm) in SI and 2.1 mm (−2.1/2.0 mm) in AP directions. The surrogate localization uncertainty minimally impacted the total PDF with a width of 0.6 mm. The target delineation uncertainty distribution 95% CIs were 5.4 mm. For the total PDF, the 95% CIs were 5.9 mm (−5.8/6.0 mm) in LR, 6.7 mm (−5.8/7.5 mm) in SI and 6.0 mm (−5.5/6.5 mm) in AP. Conclusion. This work reports the geometric uncertainty of MLC tracking for lung SABR by accounting for the main sources of uncertainties that occurred during treatment. The overall geometric uncertainty is within 6.0 mm in LR and AP directions and 6.7 mm in SI. The dominant uncertainty was the target delineation uncertainty. This geometric analysis helps put into context the range of uncertainties that may be expected during MLC tracking for lung SABR (ClinicalTrials.gov registration number: NCT02514512).

目的。这项工作的目的是报告接受肺 SABR 多叶准直器 (MLC) 跟踪治疗的患者的几何不确定性，以验证系统的准确性。方法。17 名患者被视为 MLC 跟踪肺 SABR 临床试验的一部分，使用植入肿瘤周围的电磁信标作为目标运动的替代物。研究中评估的不确定性来源包括替代目标位置不确定性、波束替代跟踪不确定性、替代定位不确定性和目标描绘不确定性。为队列和每位患者构建了每个不确定性来源的概率密度函数 (PDF)。使用卷积方法计算总 PDF。95% 置信区间 (CI) 用于量化这些不确定性。结果。对于该队列，替代目标位置不确定性 95% CI 在左右 (LR) 中为 2.5 mm (-2.0/3.0 mm)，在上下 (SI) 中为 3.0 mm (-1.6/4.5 mm) 和 2.0 mm (-1.8/2.1 mm) 前后 (AP)。光束替代跟踪不确定性 95% CI 在 LR 中为 2.1 mm (-2.1/2.1 mm)，在 SI 中为 2.8 mm (-2.8/2.7 mm)，在 AP 方向上为 2.1 mm (-2.1/2.0 mm)。替代定位不确定性对宽度为 0.6 mm 的总 PDF 的影响最小。目标描绘不确定性分布 95% CI 为 5.4 mm。对于总 PDF，LR 中的 95% CI 为 5.9 mm (-5.8/6.0 mm)，SI 中为 6.7 mm (-5.8/7.5 mm)，AP 中为 6.0 mm (-5.5/6.5 mm)。结论。这项工作通过考虑治疗期间发生的主要不确定性来源，报告了 MLC 跟踪肺 SABR 的几何不确定性。LR 和 AP 方向的整体几何不确定度在 6.0 mm 以内，SI 方向的整体几何不确定度在 6.7 mm 以内。主要的不确定性是目标描绘的不确定性。这种几何分析有助于将 MLC 跟踪肺 SABR 期间可能预期的不确定性范围纳入上下文（ClinicalTrials.gov 注册号：NCT02514512）。