Evaluating IMRT and VMAT dose accuracy: Practical examples of failure to detect systematic errors when applying a commonly used metric and action levels
Evaluating IMRT and VMAT dose accuracy: Practical examples of failure to detect systematic errors when applying a commonly used metric and action levels
复制标题
DOI：
10.1118/1.4826166
复制
发表时间：
2013-11-01
期刊：
影响因子：
3.8
通讯作者：
Feygelman, Vladimir
中科院分区：
文献类型：
--
作者：
Nelms, Benjamin E.;Chan, Maria F.;Feygelman, Vladimir
用途：本研究（1）检查了各种现实情况，其中广泛接受的IMRT/VMAT剂量测定准确性评价方法未检测到系统误差，以及（2）深入研究以识别故障模式及其相应的检测、诊断和缓解方法。详细介绍这些案例研究的主要目标是探索不同的，更敏感的方法和指标，可以更有效地用于评估剂量算法，输送系统和QA devices.Methods的准确性：作者提出了七个现实世界的案例研究，代表各种组合的治疗计划系统（TPS），直线加速器，输送方式，和系统错误类型。这些案例研究对于可能用作IMRT或VMAT调试测试套件的一部分的内容是典型的，其复杂性各不相同。根据TG-119说明对每个射束和/或复合计划剂量测定QA的伽马通过率和行动水平进行分析。然后，对每一个案例进行了深入的分析与先进的诊断方法（剂量剖面检查、基于EPID的测量、剂量差异模式分析、3D测量引导剂量重建和剂量网格检查）和更灵敏的度量（2%局部标准化/2 mm DTA和估计的DVH比较）。对于这些病例研究，IMRT每射束分析的常规3%/3 mm伽马通过率超过99%，复合计划剂量分析的通过率范围为93.9%至100%，远高于TG-119的作用水平，分别为90%和88%。然而，所有病例都有系统性错误，只有使用先进的诊断技术和更敏感的指标才能发现。系统误差造成了可变但值得注意的影响，包括估计的目标剂量覆盖率损失高达5.5%，局部剂量偏差高达31.5%。错误类型包括TPS模型设置、算法限制以及TPS中QA体模的建模和对齐。大多数的错误是可纠正的检测和诊断后，和不可纠正的错误提供了有用的信息，系统的局限性，这是另一个关键要素systemcommissions.Conclusions：许多形式的相关系统错误可以去未被检测到的IMRT/VMAT调试时，目前流行的指标。如果使用替代方法和度量来代替（或除了）常规度量，则这些错误更有可能被检测到，并且只有一旦它们被检测到，它们才能被正确地诊断并从系统中根除。消除系统误差不仅是最终用户调试的目标，也是制造商产品验证的目标。对于任何无法消除的系统误差，检测和量化它们非常重要，因为这将有助于物理学家了解系统的局限性，并与制造商合作进行改进。总之，IMRT和VMAT调试以及产品确认沿着将受益于3%/3 mm通过率作为主要性能指标的淘汰，以及采用而不是更严格的公差、更勤奋的诊断和更彻底的分析。(C)2013年美国医学物理学家协会。
Purpose: This study (1) examines a variety of real-world cases where systematic errors were not detected by widely accepted methods for IMRT/VMAT dosimetric accuracy evaluation, and (2) drills-down to identify failure modes and their corresponding means for detection, diagnosis, and mitigation. The primary goal of detailing these case studies is to explore different, more sensitive methods and metrics that could be used more effectively for evaluating accuracy of dose algorithms, delivery systems, and QA devices.Methods: The authors present seven real-world case studies representing a variety of combinations of the treatment planning system (TPS), linac, delivery modality, and systematic error type. These case studies are typical to what might be used as part of an IMRT or VMAT commissioning test suite, varying in complexity. Each case study is analyzed according to TG-119 instructions for gamma passing rates and action levels for per-beam and/or composite plan dosimetric QA. Then, each case study is analyzed in-depth with advanced diagnostic methods (dose profile examination, EPID-based measurements, dose difference pattern analysis, 3D measurement-guided dose reconstruction, and dose grid inspection) and more sensitive metrics (2% local normalization/2 mm DTA and estimated DVH comparisons).Results: For these case studies, the conventional 3%/3 nun gamma passing rates exceeded 99% for IMRT per-beam analyses and ranged from 93.9% to 100% for composite plan dose analysis, well above the TG-119 action levels of 90% and 88%, respectively. However, all cases had systematic errors that were detected only by using advanced diagnostic techniques and more sensitive metrics. The systematic errors caused variable but noteworthy impact, including estimated target dose coverage loss of up to 5.5% and local dose deviations up to 31.5%. Types of errors included TPS model settings, algorithm limitations, and modeling and alignment of QA phantoms in the TPS. Most of the errors were correctable after detection and diagnosis, and the uncorrectable errors provided useful information about system limitations, which is another key element of system commissioning.Conclusions: Many forms of relevant systematic errors can go undetected when the currently prevalent metrics for IMRT/VMAT commissioning are used. If alternative methods and metrics are used instead of (or in addition to) the conventional metrics, these errors are more likely to be detected, and only once they are detected can they be properly diagnosed and rooted out of the system. Removing systematic errors should be a goal not only of commissioning by the end users but also product validation by the manufacturers. For any systematic errors that cannot be removed, detecting and quantifying them is important as it will help the physicist understand the limits of the system and work with the manufacturer on improvements. In summary, IMRT and VMAT commissioning, along with product validation, would benefit from the retirement of the 3%/3 mm passing rates as a primary metric of performance, and the adoption instead of tighter tolerances, more diligent diagnostics, and more thorough analysis. (C) 2013 American Association of Physicists in Medicine.