Validation of a deformable image registration technique for cone beam CT-based dose verification
Validation of a deformable image registration technique for cone beam CT-based dose verification
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DOI：
10.1118/1.4903292
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发表时间：
2015-01-01
期刊：
影响因子：
3.8
通讯作者：
Lu, H. -M.
中科院分区：
文献类型：
--
作者：
Moteabbed, M.;Sharp, G. C.;Lu, H. -M.
目的：随着放射治疗向更具适应性的技术发展，图像引导不仅在患者设置中，而且在监测输送剂量和使治疗适应患者变化方面发挥着越来越重要的作用。本研究旨在验证一种基于多模式可变形图像配准（IMRT）的前列腺治疗剂量评估方法：采用CT和锥形束计算机断层扫描（CBCT）扫描骨盆体模。使用两个逼真的基于患者的变形场对两个图像进行数字变形。然后将原始CT与变形CBCT配准，得到二次变形CT。配准质量被评估为恢复人工引起的变形的方法的能力。比较原发和继发变形CT图像以及矢量场，以评价配准方法的有效性及其用于剂量计算的适用性PLASTIMATCH，一种用于变形图像配准的免费开源软件。为了获得最佳的配准质量，采用了一种参数优化的B样条算法。通过基于体素的Hounsfield单位（HU）和矢量场比较进行几何图像评价。对于剂量测定评价，在原始CT图像上创建并优化IMRT治疗计划，并在两个扭曲图像上重新计算以进行比较。比较了两个翘曲图像中相同的翘曲结构的剂量体积直方图。重复此过程的幻影与充分，半满，空blader.Results：结果表明，平均HU之间的差异高达120注册和地面真实变形的CT图像。然而，当使用基于感兴趣区域（ROI）的校准曲线校准CBCT强度时，这些差异减少了60%。同样，在配准前校准CBCT时，平均向量场长度的平均差异从10.1 mm降至2.5 mm。结果表明，膀胱充盈水平没有依赖性。与在初次变形CT上计算的剂量相比，对于全膀胱场景，在有和没有CBCT校准的情况下，在二次变形CT上计算的剂量在所有器官上平均的平均剂量差异分别为0.2%和3.9%，在校准CBCT上直接计算的剂量差异为0.5%。伽玛分析的距离，以协议的2毫米和2%的规定剂量表明，通过率为100%的两种情况下，涉及校准CBCT和平均86%没有CBCT calibration.Conclusions：使用变形配准的计划CT图像，以评估IMRT剂量的基础上，每天CBCT是可行的。所提出的方法将使用计划CT和预处理CBCT数据提供准确的剂量分布，避免由CBCT不均匀性和伪影引入的额外不确定性。这是迈向未来前列腺图像引导自适应放射治疗的必要的第一步。(c)2015年美国医学物理学家协会。
Purpose: As radiation therapy evolves toward more adaptive techniques, image guidance plays an increasingly important role, not only in patient setup but also in monitoring the delivered dose and adapting the treatment to patient changes. This study aimed to validate a method for evaluation of delivered intensity modulated radiotherapy (IMRT) dose based on multimodal deformable image registration (DIR) for prostate treatments.Methods: A pelvic phantom was scanned with CT and cone-beam computed tomography (CBCT). Both images were digitally deformed using two realistic patient-based deformation fields. The original CT was then registered to the deformed CBCT resulting in a secondary deformed CT. The registration quality was assessed as the ability of the DIR method to recover the artificially induced deformations. The primary and secondary deformed CT images as well as vector fields were compared to evaluate the efficacy of the registration method and it's suitability to be used for dose calculation PLASTIMATCH, a free and open source software was used for deformable image registration. A B-spline algorithm with optimized parameters was used to achieve the best registration quality. Geometric image evaluation was performed through voxel-based Hounsfield unit (HU) and vector field comparison. For dosimetric evaluation, IMRT treatment plans were created and optimized on the original CT image and recomputed on the two warped images to be compared. The dose volume histograms were compared for the warped structures that were identical in both warped images. This procedure was repeated for the phantom with full, half full, and empty bladder.Results: The results indicated mean HU differences of up to 120 between registered and ground-truth deformed CT images. However, when the CBCT intensities were calibrated using a region of interest (ROI)-based calibration curve, these differences were reduced by up to 60%. Similarly, the mean differences in average vector field lengths decreased from 10.1 to 2.5 mm when CBCT was calibrated prior to registration. The results showed no dependence on the level of bladder filling. In comparison with the dose calculated on the primary deformed CT, differences in mean dose averaged over all organs were 0.2% and 3.9% for dose calculated on the secondary deformed CT with and without CBCT calibration, respectively, and 0.5% for dose calculated directly on the calibrated CBCT, for the full-bladder scenario. Gamma analysis for the distance to agreement of 2 mm and 2% of prescribed dose indicated a pass rate of 100% for both cases involving calibrated CBCT and on average 86% without CBCT calibration.Conclusions: Using deformable registration on the planning CT images to evaluate the IMRT dose based on daily CBCTs was found feasible. The proposed method will provide an accurate dose distribution using planning CT and pretreatment CBCT data, avoiding the additional uncertainties introduced by CBCT inhomogeneity and artifacts. This is a necessary initial step toward future image-guided adaptive radiotherapy of the prostate. (c) 2015 American Association of Physicists in Medicine.