A patch-based pseudo-CT approach for MRI-only radiotherapy in the pelvis
A patch-based pseudo-CT approach for MRI-only radiotherapy in the pelvis
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DOI：
10.1118/1.4958676
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发表时间：
2016-08-01
期刊：
影响因子：
3.8
通讯作者：
Edmund, Jens M.
中科院分区：
文献类型：
--
作者：
Andreasen, Daniel;Van Leemput, Koen;Edmund, Jens M.
目的：在仅基于磁共振成像（MRI）的放射治疗中，有关组织电子密度的知识必须来自MRI。这可以通过将MRI扫描转换为所谓的伪计算机断层扫描（pCT）来实现。一个障碍是常规MRI扫描中的体素强度不是唯一地与电子密度相关。作者之前证明，基于贴片的方法可以使用传统的Ti加权MRI扫描产生准确的脑部pCT。该方法主要由局部补丁相似性驱动，并依赖于共同配准的MRI/CT扫描对的图谱数据库与待转换的MRI扫描之间的简单仿射配准。在这项研究中，作者研究了基于补丁的方法在骨盆中的适用性。该区域对于基于局部相似性的方法是具有挑战性的，因为患者间的变化更大。作者将该方法与基线pCT策略进行了基准测试，其中身体轮廓内的所有体素都被分配了水当量体积密度。此外，作者实现了一个并行近似补丁搜索策略，以加快pCT生成时间到一个更临床相关的level.Methods：数据包括10例前列腺患者的CT和T-1加权MRI扫描。使用近似补丁搜索算法以留一法生成pCT，并与使用频繁描述的度量（如逐体素平均绝对误差（MAE（VOX））和水等效路径长度偏差）的CT进行比较。此外，剂量测定的准确性进行了测试的体积调制弧治疗计划，使用剂量体积直方图（DVH）点偏差和伽玛指数analysis.Results：补丁为基础的方法有一个平均MAE，x为54 HU的中位偏差小于0.4%，在相关的DVH点和伽玛指数通过率为0.97，使用1%/1毫米的标准。基于补丁的方法在几乎所有指标中显示出比基线水pCT显著更好的性能。近似补丁搜索策略比蛮力搜索快70倍，平均预测时间为20.8 min。结论：作者表明，基于仿射配准和T-1加权MRI的补丁方法可以生成准确的骨盆pCT。pCT与CT之间的差异主要来源于气囊和身体轮廓的位置变化。(C)2016年美国医学物理学家协会。
Purpose: In radiotherapy based only on magnetic resonance imaging (MRI), knowledge about tissue electron densities must be derived from the MRI. This can be achieved by converting the MRI scan to the so-called pseudo-computed tomography (pCT). An obstacle is that the voxel intensities in conventional MRI scans are not uniquely related to electron density. The authors previously demonstrated that a patch-based method could produce accurate pCTs of the brain using conventional Ti-weighted MRI scans. The method was driven mainly by local patch similarities and relied on simple affine registrations between an atlas database of the co-registered MRI/CT scan pairs and the MRI scan to be converted. In this study, the authors investigate the applicability of the patch-based approach in the pelvis. This region is challenging for a method based on local similarities due to the greater inter-patient variation. The authors benchmark the method against a baseline pCT strategy where all voxels inside the body contour are assigned a water-equivalent bulk density. Furthermore, the authors implement a parallelized approximate patch search strategy to speed up the pCT generation time to a more clinically relevant level.Methods: The data consisted of CT and T-1-weighted MRI scans of 10 prostate patients. pCTs were generated using an approximate patch search algorithm in a leave-one-out fashion and compared with the CT using frequently described metrics such as the voxel-wise mean absolute error (MAE(VOX)) and the deviation in water-equivalent path lengths. Furthermore, the dosimetric accuracy was tested for a volumetric modulated arc therapy plan using dose volume histogram (DVH) point deviations and gamma-index analysis.Results: The patch-based approach had an average MAE,x of 54 HU; median deviations of less than 0.4% in relevant DVH points and a gamma-index pass rate of 0.97 using a 1%/1 mm criterion. The patch-based approach showed a significantly better performance than the baseline water pCT in almost all metrics. The approximate patch search strategy was 70x faster than a brute-force search, with an average prediction time of 20.8 min.Conclusions: The authors showed that a patch-based method based on affine registrations and T-1-weighted MRI could generate accurate pCTs of the pelvis. The main source of differences between pCT and CT was positional changes of air pockets and body outline. (C) 2016 American Association of Physicists in Medicine.