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首页> 外文期刊>Medical Physics >Image‐guided radiotherapy quality control: Statistical process control using image similarity metrics
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Image‐guided radiotherapy quality control: Statistical process control using image similarity metrics

机译：图像引导放射疗法质量控制：使用图像相似度量控制统计过程控制

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Purpose The purpose of this study was to demonstrate an objective quality control framework for the image review process. Methods and materials A total of 927 cone‐beam computed tomography ( CBCT ) registrations were retrospectively analyzed for 33 bilateral head and neck cancer patients who received definitive radiotherapy. Two registration tracking volumes ( RTV s) — cervical spine (C‐spine) and mandible — were defined, within which a similarity metric was calculated and used as a registration quality tracking metric over the course of treatment. First, sensitivity to large misregistrations was analyzed for normalized cross‐correlation ( NCC ) and mutual information ( MI ) in the context of statistical analysis. The distribution of metrics was obtained for displacements that varied according to a normal distribution with standard deviation of σ = 2 mm, and the detectability of displacements greater than 5 mm was investigated. Then, similarity metric control charts were created using a statistical process control ( SPC ) framework to objectively monitor the image registration and review process. Patient‐specific control charts were created using NCC values from the first five fractions to set a patient‐specific process capability limit. Population control charts were created using the average of the first five NCC values for all patients in the study. For each patient, the similarity metrics were calculated as a function of unidirectional translation, referred to as the effective displacement. Patient‐specific action limits corresponding to 5 mm effective displacements were defined. Furthermore, effective displacements of the ten registrations with the lowest similarity metrics were compared with a three dimensional (3DoF) couch displacement required to align the anatomical landmarks. Results Normalized cross‐correlation identified suboptimal registrations more effectively than MI within the framework of SPC . Deviations greater than 5 mm were detected at 2.8σ and 2.1σ from the mean for NCC and MI , respectively. Patient‐specific control charts using NCC evaluated daily variation and identified statistically significant deviations. This study also showed that subjective evaluations of the images were not always consistent. Population control charts identified a patient whose tracking metrics were significantly lower than those of other patients. The patient‐specific action limits identified registrations that warranted immediate evaluation by an expert. When effective displacements in the anterior–posterior direction were compared to 3DoF couch displacements, the agreement was ±1 mm for seven of 10 patients for both C‐spine and mandible RTV s. Conclusions Qualitative review alone of IGRT images can result in inconsistent feedback to the IGRT process. Registration tracking using NCC objectively identifies statistically significant deviations. When used in conjunction with the current image review process, this tool can assist in improving the safety and consistency of the IGRT process.
机译：目的本研究的目的是展示图像审查过程的客观质量控制框架。方法和材料总共927个锥形束计算断层扫描（CBCT）注册，用于33种接受明确放疗的双侧头部和颈部癌症患者进行了回顾性分析。定义了两个登记跟踪体积（RTV S） - 颈椎（C-SPINE）和下颌骨 - 在其中计算相似度量并用作治疗过程中的登记质量跟踪度量。首先，在统计分析的背景下分析对归一化互相关（NCC）和互信息（MI）对大错误分析的敏感性。获得测量标准的分布对于根据正常分布而变化的位移，标准偏差为σ= 2mm，并且研究了大于5mm的位移的可检测性。然后，使用统计过程控制（SPC）框架创建相似度量控制图来客观监控图像注册和审阅过程。使用来自前五个分数的NCC值创建特定于患者的控制图，以设定特定于患者的过程能力限制。使用该研究中所有患者的前五个NCC值的平均值创建人口控制图。对于每位患者，将相似度指标计算为单向翻译的函数，称为有效位移。定义了对应于5mm有效位移的患者特定的动作限制。此外，将具有最低相似度量的10个注册的有效位移与三维（3DOF）沙发位移进行比较，以对准解剖学标志。结果归一化交叉相关在SPC框架内比MI更有效地识别了次优注册。在2.8σ和2.1σ中分别从NCC和Mi的平均值检测大于5mm的偏差。使用NCC评估日常变异的患者特定控制图，并确定了统计上显着的偏差。本研究还表明，图像的主观评估并不总是一致的。人口控制图确定了患者，其跟踪度量明显低于其他患者。患者特定的行动限制了确定的注册，由专家提供立即评估。当前后方向上的有效位移与3Dof沙发位移进行比较时，该协议为C-Spine和下颌骨RTV的10名患者中的7例为±1 mm。结论IGRT图像单独的定性审查可能导致IGRT过程的反馈不一致。使用NCC的注册跟踪客观地识别统计上显着的偏差。当与当前的图像审查过程结合使用时，该工具可以帮助提高IGRT过程的安全性和一致性。

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