Australian Clinical Dosimetry Service, ARPANSA, Melbourne, Australia.
Imaging and Radiation Oncology Core Houston QA Center, MD Anderson Cancer Center, Houston, TX, USA.
Med Phys. 2019 Dec;46(12):5878-5887. doi: 10.1002/mp.13800. Epub 2019 Oct 25.
Consistency between different international quality assurance groups is important in the progress toward similar standards and expectations in radiotherapy dosimetry around the world, and in the context of consistent clinical trial data from international trial participants. This study compares the dosimetry audit methodology and results of two international quality assurance groups performing a side-by-side comparison at the same radiotherapy department, and interrogates the ability of the audits to detect deliberately introduced errors.
A comparison of the core dosimetry components of reference and non-reference audits was conducted by the Imaging and Radiation Oncology Core (IROC, Houston, USA) and the Australian Clinical Dosimetry Service (ACDS, Melbourne, Australia). A set of measurements were conducted over 2 days at an Australian radiation therapy facility in Melbourne. Each group evaluated the reference dosimetry, output factors, small field output factors, percentage depth dose (PDD), wedge, and off-axis factors according to their standard protocols. IROC additionally investigated the Electron PDD and the ACDS investigated the effect of heterogeneities. In order to evaluate and compare the performance of these audits under suboptimal conditions, artificial errors in percentage depth dose (PDD), EDW, and small field output factors were introduced into the 6 MV beam model to simulate potential commissioning/modeling errors and both audits were tested for their sensitivity in detecting these errors.
With the plans from the clinical beam model, almost all results were within tolerance and at an optimal pass level. Good consistency was found between the two audits as almost all findings were consistent between them. Only two results were different between the results of IROC and the ACDS. The measurements of reference FFF photons showed a discrepancy of 0.7% between ACDS and IROC due to the inclusion of a 0.5% nonuniformity correction by the ACDS. The second difference between IROC and the ACDS was seen with the lung phantom. The asymmetric field behind lung measured by the ACDS was slightly (0.3%) above the ACDS's pass (optimal) level of 3.3%. IROC did not detect this issue because their measurements were all assessed in a homogeneous phantom. When errors were deliberately introduced neither audit was sensitive enough to pick up a 2% change to the small field output factors. The introduced PDD change was flagged by both audits. Similarly, the introduced error of using 25° wedge instead of 30° wedge was detectible in both audits as out of tolerance.
Despite different equipment, approach, and scope of measurements in on-site audits, there were clear similarities between the results from the two groups. This finding is encouraging in the context of a global harmonized approach to radiotherapy quality assurance and dosimetry audit.
在全球范围内，不同国际质量保证组织之间的一致性对于放射治疗剂量学达到类似标准和期望非常重要，对于来自国际试验参与者的一致临床试验数据也是如此。本研究比较了两个国际质量保证组织在同一放射治疗部门进行的并排比较的剂量学审核方法和结果，并探讨了审核检测到故意引入错误的能力。
由美国休斯顿的成像和放射肿瘤学核心（IROC）和澳大利亚临床剂量服务（ACDS）对参考和非参考审核的核心剂量学组件进行了比较。在墨尔本的一家澳大利亚放射治疗机构进行了为期两天的一组测量。每个组都根据其标准协议评估参考剂量、输出因子、小射野输出因子、百分深度剂量（PDD）、楔形板和离轴因子。IROC 还研究了电子 PDD，而 ACDS 则研究了不均匀性的影响。为了评估和比较在次优条件下这些审核的性能，将人工误差引入到 6MV 射束模型中的百分深度剂量（PDD）、EDW 和小射野输出因子中，以模拟潜在的调试/建模误差，并测试这两个审核检测这些误差的灵敏度。
对于临床射束模型的计划，几乎所有结果都在容差内，并且处于最佳通过水平。两个审核之间发现了很好的一致性，因为几乎所有的发现都与它们一致。只有两个结果在 IROC 和 ACDS 的结果之间存在差异。由于 ACDS 包含了 0.5%的不均匀性校正，参考 FFF 光子的测量结果与 ACDS 和 IROC 之间存在 0.7%的差异。IROC 和 ACDS 之间的第二个差异是在肺体模中看到的。ACDS 测量的肺后面的不对称射野略高于 ACDS （最佳）水平 3.3%（0.3%）。IROC 没有检测到这个问题，因为他们的测量都是在均匀体模中进行的。当故意引入误差时，两个审核都没有足够的灵敏度来检测小射野输出因子的 2%变化。两个审核都标记了引入的 PDD 变化。同样，使用 25°楔形板而不是 30°楔形板的引入误差在两个审核中都被检测到超出容差。
尽管现场审核的设备、方法和测量范围不同，但两个组的结果之间存在明显的相似性。在全球放射治疗质量保证和剂量学审核的协调方法背景下，这一发现令人鼓舞。
