Dept. of Radiation Oncology, Beaumont Health System, Royal Oak, MI, USA.
Elekta Inc., Maryland Heights, MO, 63043, USA.
Med Phys. 2018 Mar;45(3):1287-1294. doi: 10.1002/mp.12741. Epub 2018 Jan 20.
The purpose of this study was to investigate the clinical-relevant discrepancy between doses warped by pure image based deformable image registration (IM-DIR) and by biomechanical model based DIR (BM-DIR) on intensity-homogeneous organs.
Ten patients (5Head&Neck, 5Prostate) were included. A research DIR tool (ADMRIE_v1.12) was utilized for IM-DIR. After IM-DIR, BM-DIR was carried out for organs (parotids, bladder, and rectum) which often encompass sharp dose gradient. Briefly, high-quality tetrahedron meshes were generated and deformable vector fields (DVF) from IM-DIR were interpolated to the surface nodes of the volume meshes as boundary condition. Then, a FEM solver (ABAQUS_v6.14) was used to simulate the displacement of internal nodes, which were then interpolated to image-voxel grids to get the more physically plausible DVF. Both geometrical and subsequent dose warping discrepancies were quantified between the two DIR methods. Target registration discrepancy(TRD) was evaluated to show the geometry difference. The re-calculated doses on second CT were warped to the pre-treatment CT via two DIR. Clinical-relevant dose parameters and γ passing rate were compared between two types of warped dose. The correlation was evaluated between parotid shrinkage and TRD/dose discrepancy.
The parotid shrunk to 75.7% ± 9% of its pre-treatment volume and the percentage of volume with TRD>1.5 mm) was 6.5% ± 4.7%. The normalized mean-dose difference (NMDD) of IM-DIR and BM-DIR was -0.8% ± 1.5%, with range (-4.7% to 1.5%). 2 mm/2% passing rate was 99.0% ± 1.4%. A moderate correlation was found between parotid shrinkage and TRD and NMDD. The bladder had a NMDD of -9.9% ± 9.7%, with BM-DIR warped dose systematically higher. Only minor deviation was observed for rectum NMDD (0.5% ± 1.1%).
Impact of DIR method on treatment dose warping is patient and organ-specific. Generally, intensity-homogeneous organs, which undergo larger deformation/shrinkage during treatment and encompass sharp dose gradient, will have greater dose warping uncertainty. For these organs, BM-DIR could be beneficial to the evaluation of DIR/dose-warping uncertainty.
本研究旨在探讨基于纯图像的形变图像配准（IM-DIR）和基于生物力学模型的形变图像配准（BM-DIR）在剂量学上对均匀密度器官的临床相关差异。
本研究纳入了 10 名患者（5 名头颈部，5 名前列腺）。使用研究型形变图像配准工具（ADMRIE_v1.12）进行 IM-DIR。在 IM-DIR 之后，对经常包含陡峭剂量梯度的器官（腮腺、膀胱和直肠）进行 BM-DIR。简要来说，生成高质量的四面体网格，并将 IM-DIR 中的可变形矢量场（DVF）插值到体网格的表面节点作为边界条件。然后，使用有限元求解器（ABAQUS_v6.14）模拟内部节点的位移，然后将其插值到图像体素网格中，以获得更符合物理规律的 DVF。定量评估了两种 DIR 方法之间的几何和后续剂量扭曲差异。通过两种 DIR 将第二次 CT 上的计算剂量扭曲到预处理 CT。比较两种扭曲剂量的临床相关剂量参数和γ通过率。评估了腮腺收缩与 TRD/剂量差异之间的相关性。
腮腺体积缩小到治疗前的 75.7%±9%，TRD>1.5mm 的体积百分比为 6.5%±4.7%。IM-DIR 和 BM-DIR 的归一化平均剂量差异（NMDD）为-0.8%±1.5%，范围为-4.7%至 1.5%。2mm/2%通过率为 99.0%±1.4%。腮腺收缩与 TRD 和 NMDD 之间存在中度相关性。膀胱的 NMDD 为-9.9%±9.7%，BM-DIR 扭曲剂量普遍较高。直肠 NMDD 仅略有偏差（0.5%±1.1%）。
DIR 方法对治疗剂量扭曲的影响具有患者和器官特异性。一般来说，在治疗过程中发生较大变形/收缩且包含陡峭剂量梯度的均匀密度器官将具有更大的剂量扭曲不确定性。对于这些器官，BM-DIR 有助于评估 DIR/剂量扭曲不确定性。
