Purpose: Trajectory log files are increasingly being utilized clinically for machine and patient specific QA. The process of converting the DICOM-RT plan to a deliverable trajectory by the linac control software introduces some uncertainty that is inherently incorporated into measurement-based patient specific QA but is not necessarily included for trajectory log file-based methods. Roughly half of prior studies have included this uncertainty in the analysis while the remaining studies have ignored it, and it has yet to be quantified in the literature. Methods: We collected DICOM-RT files from the treatment planning system and the trajectory log files from four TrueBeam linear accelerators for 25 IMRT and 10 VMAT plans. We quantified the DICOM-RT Conversion to Trajectory Residual (DCTR, difference between ‘planned’ MLC position from TPS DICOM-RT file and ‘expected’ MLC position (the deliverable MLC positions calculated by the linac control software) from trajectory log file) and compared it to the discrepancy between actual and expected machine parameters recorded in trajectory log files. Results: RMS of the DCTR was 0.0845 mm (range of RMS per field/arc: 0.0173–0.1825 mm) for 35 plans (114 fields/arcs) and was independent of treatment technique, with a maximum observed discrepancy at any control point of 0.7255 mm. DCTR was correlated with MLC velocity and was consistent over the course of treatment and over time, with a slight change in magnitude observed after a linac software upgrade. For comparison, the RMS of trajectory log file reported delivery error for moving MLCs was 0.0205 mm, thus DCTR is about four times the recorded delivery error in the trajectory log file. Conclusion: The uncertainty introduced from the conversion process by the linac control software from DICOM-RT plan to a deliverable trajectory is 3–4 times larger than the discrepancy between actual and expected machine parameters recorded in trajectory log files. This uncertainty should be incorporated into the analysis when using trajectory log file-based methods for analyzing MLC performance or patient-specific QA.

目的：轨迹日志文件越来越多地在临床上用于机器和患者特定的 QA。通过直线加速器控制软件将 DICOM-RT 计划转换为可交付轨迹的过程引入了一些不确定性，这些不确定性固有地包含在基于测量的患者特定 QA 中，但不一定包含在基于轨迹日志文件的方法中。大约一半的先前研究在分析中包含了这种不确定性，而其余研究则忽略了它，并且尚未在文献中对其进行量化。方法：我们从治疗计划系统中收集了 DICOM-RT 文件，并从四个 TrueBeam 直线加速器中收集了 25 个 IMRT 和 10 个 VMAT 计划的轨迹日志文件。我们量化了 DICOM-RT 到轨迹残差的转换（DCTR，来自 TPS DICOM-RT 文件的“计划”MLC 位置与来自轨迹日志文件的“预期”MLC 位置（由直线加速器控制软件计算的可交付 MLC 位置）之间的差异）和将其与轨迹日志文件中记录的实际和预期机器参数之间的差异进行比较。结果：对于 35 个计划（114 个视野/弧），DCTR 的 RMS 为 0.0845 毫米（每个视野/弧的 RMS 范围：0.0173-0.1825 毫米）并且与治疗技术无关，在任何控制点观察到的最大差异为 0.7255 毫米。DCTR 与 MLC 速度相关，并且在治疗过程中和随着时间的推移保持一致，在 linac 软件升级后观察到的幅度略有变化。相比之下，轨迹日志文件的 RMS 报告移动 MLC 的传递误差为 0.0205 毫米，因此 DCTR 大约是轨迹日志文件中记录的传递误差的四倍。结论：直线加速器控制软件从 DICOM-RT 计划到可交付轨迹的转换过程中引入的不确定性比轨迹日志文件中记录的实际和预期机器参数之间的差异大 3-4 倍。当使用基于轨迹日志文件的方法来分析 MLC 性能或特定于患者的 QA 时，应将这种不确定性纳入分析中。