Medical Physics Unit, Second Department of Radiology, Medical School, National and Kapodistrian University of Athens, University General Hospital "Attikon", Haidari, Athens, Greece.
Radiation Therapy Unit, Second Department of Radiology, Medical School, National and Kapodistrian University of Athens, University General Hospital "Attikon", Haidari, Athens, Greece.
Med Phys. 2022 Jul;49(7):4322-4334. doi: 10.1002/mp.15703. Epub 2022 May 23.
To determine the tolerance limit (TL) and action limit (AL) of gamma passing rates (%GP) for volumetric-modulated arc therapy (VMAT) patient-specific quality assurance (PSQA) according to the American Association of Physicists in Medicine (AAPM) Task Group (TG)-218 recommendations, and to comparatively evaluate the clinical relevance of 2D %GP and 3D %GP.
PSQA was performed for 100 head and neck (H&N) and 73 prostate cancer VMAT treatment plans. Measurements were acquired using a cylindrical water equivalent phantom, hollow in the center, allowing measurements with homogeneous or heterogeneous inserts. The LINAC-delivered dose distributions were compared to those calculated from the treatment planning system through the gamma index. TL and AL were determined through the computation of two-dimensional (2D) %GP using the recommended acceptance criteria. Dose-volume histograms were reconstructed from the measurements using a commercially available software to detect the dosimetric errors (%DE) between the compared dose distributions. Utilizing the estimated dose on the patient anatomy, structure-specific %GP (3D %GP) were calculated. The 3D %GP were compared to the 2D %GP ones based on their correlation with the %DE. Each metric's sensitivity was determined through receiver operator characteristic analysis.
TL and AL were in concordance with the universal ones, regarding the prostate cancer cases, but were lower for the H&N cases. Evaluation of %DE did not deem the plans unacceptable. The 2D %GP and the 3D %GP did not differ significantly regarding their correlation with %DE. For prostate plans, %GP sensitivity was higher than for H&N cases.
Determination of institutional-specific TL and AL allows the monitoring of the PSQA procedure, yet for plans close to the limits, clinically relevant metrics should be used before they are deemed unacceptable for the process to be of higher sensitivity and efficiency.
根据美国医学物理学家协会（AAPM）TG-218 建议，确定容积调制弧形治疗（VMAT）患者特定质量保证（PSQA）的伽马通过率（%GP）的公差限（TL）和行动限（AL），并比较 2D %GP 和 3D %GP 的临床相关性。
对 100 例头颈部（H&N）和 73 例前列腺癌 VMAT 治疗计划进行 PSQA。使用圆柱形水等效体模进行测量，体模中心为空心，允许使用均匀或不均匀的插入物进行测量。通过伽马指数比较 LINAC 传递的剂量分布与从治疗计划系统计算出的剂量分布。通过使用推荐的验收标准计算二维（2D）%GP 来确定 TL 和 AL。使用商业上可用的软件从测量结果重建剂量体积直方图，以检测比较剂量分布之间的剂量误差（%DE）。利用患者解剖结构上的估计剂量，计算结构特异性的 3D %GP（3D %GP）。根据与 %DE 的相关性，将 3D %GP 与 2D %GP 进行比较。通过接收者操作特性分析确定每个指标的灵敏度。
TL 和 AL 与前列腺癌病例的通用标准一致，但与 H&N 病例的标准相比有所降低。%DE 的评估并不认为计划不可接受。2D %GP 和 3D %GP 在与 %DE 的相关性方面没有显著差异。对于前列腺计划，%GP 的灵敏度高于 H&N 病例。
确定机构特定的 TL 和 AL 可以监测 PSQA 程序，但对于接近限制的计划，在认为该过程的灵敏度和效率更高之前，应使用临床相关指标。
