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Phys Med Biol. 2018 Feb 21;63(4):045026. doi: 10.1088/1361-6560/aa9dc2.
A prerequisite for adaptive dose-tracking in radiotherapy is the assessment of the deformable image registration (DIR) quality. In this work, various metrics that quantify DIR uncertainties are investigated using realistic deformation fields of 26 head and neck and 12 lung cancer patients. Metrics related to the physiologically feasibility (the Jacobian determinant, harmonic energy (HE), and octahedral shear strain (OSS)) and numerically robustness of the deformation (the inverse consistency error (ICE), transitivity error (TE), and distance discordance metric (DDM)) were investigated. The deformable registrations were performed using a B-spline transformation model. The DIR error metrics were log-transformed and correlated (Pearson) against the log-transformed ground-truth error on a voxel level. Correlations of r ⩾ 0.5 were found for the DDM and HE. Given a DIR tolerance threshold of 2.0 mm and a negative predictive value of 0.90, the DDM and HE thresholds were 0.49 mm and 0.014, respectively. In conclusion, the log-transformed DDM and HE can be used to identify voxels at risk for large DIR errors with a large negative predictive value. The HE and/or DDM can therefore be used to perform automated quality assurance of each CT-based DIR for head and neck and lung cancer patients.
自适应剂量跟踪在放射治疗中的一个前提是评估可变形图像配准（DIR）的质量。在这项工作中，使用 26 例头颈部和 12 例肺癌患者的真实变形场研究了各种量化 DIR 不确定性的指标。研究了与变形的生理可行性（雅可比行列式、调和能量（HE）和八面体剪切应变（OSS））和数值稳健性（逆一致性误差（ICE）、传递误差（TE）和距离不一致性度量（DDM））相关的度量。使用 B 样条变换模型进行可变形配准。将 DIR 误差指标进行对数变换，并在体素水平上与地面真实误差的对数变换进行相关（Pearson）。DDM 和 HE 的相关系数 r ⁇ ⁇ ⁇ 0.5。给定 DIR 容限阈值为 2.0mm 和负预测值为 0.90，DDM 和 HE 的阈值分别为 0.49mm 和 0.014。总之，对数变换的 DDM 和 HE 可用于识别存在大 DIR 误差风险的体素，且具有较大的负预测值。因此，HE 和/或 DDM 可用于对头颈部和肺癌患者的每个基于 CT 的 DIR 进行自动质量保证。
