弥合差距：Varian TrueBeam 直线加速器的双站点 MLC 间隙匹配研究
Closing the gap: A two-site MLC matching study for Varian TrueBeam Linear Accelerators
AI总结：
本研究通过四种方法协调四台TrueBeam加速器的MLC间隙校准，调整后TS1和TS5接近参考范围，并优化RayStation偏移参数提升VMAT计划通过率至94.8%以上。
AI中文摘要：
目的：表征并协调四台射束匹配的 TrueBeam 加速器的多叶准直器（MLC）间隙校准，并评估一个通用的治疗计划系统模型。方法：研究了四台 Millennium 120 TrueBeams：TS1（2016 年安装）、TS5（2021 年）、TS6 和 TS7（2024 年）。间隙校准通过 RayStation 扫描间隙测量、塞尺、基于 EPID 的 Stakitt Fence 测试以及叶片分辨率的机器性能检查（MPC）进行评估。TS1 和 TS5 在维修模式下进行了调整，TS5 还调整了 MLC 中心线偏移。十个临床 VMAT 计划以及六个先前在未调整的参考机器上采集的计划，使用 ArcCHECK 1220 进行测量，并与 RayStation 中 0.053 和 0.065 cm x 偏移量处计算的剂量进行比较。结果：2024 年的机器具有更宽的基线间隙。所有四种方法均记录到 TS1 和 TS5 的变化方向一致，且与预测值相差在 0.060 mm 以内。调整后，TS1 和 TS5 落在 TS6/TS7 的扫描间隙和 Stakitt 范围内，但在塞尺上读数更宽。在 TS5 上进行的传统栅栏测试未记录到变化。提高 RayStation x 偏移参数使 TS1 的平均局部 3%/2 mm 通过率从 92.3% 提高到 94.8%，TS5 从 93.2% 提高到 95.6%；所有 24 个计划-标准对在未调整的机器上均有所改善。结论：机械、EPID 和扫描间隙 MLC 间隙测量对 MLC 调整响应一致，使 TS1 和 TS5 向本地参考范围靠拢。所有全局 3%/2 mm ArcCHECK 测量均超过 TG-218 的 95% 限值。
英文摘要：
Purpose: To characterise and harmonise multileaf collimator (MLC) gap calibrations across four beam-matched TrueBeams and assess a common planning-system model. Methods: Four Millennium 120 TrueBeams were studied: TS1 (installed 2016), TS5 (2021), TS6 and TS7 (2024). Gap calibration was assessed by RayStation sweeping-gap measurement, feeler gauge, the EPID-based Stakitt Fence test, and a leaf-resolved Machine Performance Check (MPC). TS1 and TS5 were adjusted in service mode, TS5 also for MLC centreline offset. Ten clinical VMAT plans, and six acquired earlier on an unadjusted reference machine, were measured with an ArcCHECK 1220 against doses computed at 0.053 and 0.065 cm x-offsets in RayStation. Results: The 2024 machines had wider baseline gaps. All four methods registered the TS1 and TS5 changes in the same direction and within 0.060 mm of predictions. After adjustment TS1 and TS5 lay within the TS6/TS7 sweeping-gap and Stakitt ranges but read wider on the feeler gauge. A conventional picket-fence test on TS5 registered no change. Raising the RayStation x-offset parameter increased mean local 3%/2 mm pass rates from 92.3% to 94.8% on TS1 and 93.2% to 95.6% on TS5; all 24 plan-criterion pairs improved on the unadjusted machine. Conclusions: Mechanical, EPID, and sweeping gap MLC gap measurements responded consistently to the MLC adjustment, moving TS1 and TS5 towards the local reference range. Every global 3%/2 mm ArcCHECK measurement exceeded the TG-218 95% limit.
