Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
Med Phys. 2022 Jan;49(1):611-623. doi: 10.1002/mp.15375. Epub 2021 Dec 10.
We present a DVH overlay technique as a quality assurance (QA) metric for deformable image registration-based dose accumulation (DIR-DA). We use the technique to estimate the uncertainty in a DIR-DA for a revised treatment plan, and to compare two different DIR algorithms.
The required inputs to the DVH overlay workflow are deformably registered primary and secondary images, primary regions-of-interest (ROIs), and secondary dose distribution. The primary ROIs were forward warped to the secondary image, the secondary dose was inversely warped to the primary image, and the DVHs for each image were compiled. Congruent DVHs imply minimal inverse consistency error (ICE) within an ROI. For a pancreas case re-planned after 21 fractions of a 29-fraction course, the workflow was used to quantify dose accumulation error attributable to ICE, based on a hybrid contour-and-intensity-based DIR. The usefulness of the workflow was further demonstrated by assessing the performance of two DIR algorithms (one free-form intensity-based, FFIB, the other using normalized correlation coefficients, NCC, over small neighborhood patches) as applied toward kilovoltage computed tomography (kVCT)-to-megavoltage computed tomography (MVCT) registration and five-fraction dose accumulation of ten male pelvis cases.
For the re-planned pancreas case, when applying the DVH-overlay-based uncertainties the resulting accumulated dose remained compliant with all but two of the original plan objectives. Among the male pelvis cases, FFIB and NCC DIR showed good invertibility within the planning target volume (PTV), according to the DVH overlay QA results. NCC DIR exhibited better invertibility for the bladder and rectum compared with FFIB. However, compared with FFIB, NCC DIR exhibited less regional deformation for the bladder and a tendency for increased local contraction of the rectum ROI. For the five-fraction summations, ICE for the PTV V is comparable for both algorithms (FFIB 0.8 ± 0.7%, NCC 0.7 ± 0.3%). For the bladder and rectum V , ICE is greater for FFIB (1.8 ± 0.7% for bladder, 1.7 ± 0.6% for rectum) than for NCC (1.0 ± 0.3% for bladder, 1.0 ± 0.4% for rectum).
The DVH overlay technique identified instances in which a DIR exhibits favorable invertibility, implying low ICE in a DIR-based dose accumulation. Differences in the overlaid DVHs can also estimate dose accumulation errors attributable to ICE for given ROIs.
我们提出了一种剂量体积直方图（DVH）叠加技术，作为基于形变图像配准的剂量累加（DIR-DA）的质量保证（QA）指标。我们使用该技术来估计修订治疗计划的 DIR-DA 的不确定性，并比较两种不同的 DIR 算法。
DVH 叠加工作流程所需的输入包括可变形配准的主图像和次图像、主感兴趣区（ROI）和次剂量分布。将主 ROI 正向变形到次图像，将次剂量逆向变形到主图像，并编译每个图像的 DVH。一致的 DVH 意味着 ROI 内的逆一致性误差（ICE）最小。对于在 29 个分次疗程的 21 个分次后重新计划的胰腺病例，该工作流程用于根据混合轮廓和强度的 DIR 量化归因于 ICE 的剂量累加误差。通过评估两种 DIR 算法（一种基于自由形态强度的算法，FFIB，另一种使用小邻域补丁的归一化相关系数，NCC）在千伏 CT（kVCT）到兆伏 CT（MVCT）配准和十个男性骨盆病例的五次剂量累加中的性能，进一步证明了该工作流程的有用性。
对于重新计划的胰腺病例，当应用基于 DVH 叠加的不确定性时，累积剂量仍然符合原始计划目标的除两个之外的所有目标。在男性骨盆病例中，根据 DVH 叠加 QA 结果，FFIB 和 NCC DIR 在计划靶区（PTV）内表现出良好的可反转性。与 FFIB 相比，NCC DIR 对膀胱和直肠的可反转性更好。然而，与 FFIB 相比，NCC DIR 显示出膀胱的区域变形较少，直肠 ROI 局部收缩的趋势增加。对于五次剂量累加，两个算法的 PTV V 的 ICE 相当（FFIB 0.8±0.7%，NCC 0.7±0.3%）。对于膀胱和直肠 V ，FFIB 的 ICE 较大（膀胱 1.8±0.7%，直肠 1.7±0.6%），而 NCC 的 ICE 较小（膀胱 1.0±0.3%，直肠 1.0±0.4%）。
DVH 叠加技术确定了 DIR 表现出有利的可反转性的情况，这意味着基于 DIR 的剂量累加的 ICE 较低。给定 ROI 的叠加 DVH 的差异也可以估计归因于 ICE 的剂量累加误差。
