Department of Radiation Oncology, University Medical Center Utrecht, the Netherlands.
Department of Biomedical Engineering, Eindhoven University of Technology, the Netherlands.
Radiother Oncol. 2023 May;182:109506. doi: 10.1016/j.radonc.2023.109506. Epub 2023 Feb 2.
In MR-guided SBRT of pancreatic cancer, intrafraction motion is typically monitored with (interleaved) 2D cine MRI. However, tumor surroundings are often not fully captured in these images, and motion might be distorted by through-plane movement. In this study, the feasibility of highly accelerated 3D cine MRI to reconstruct the delivered dose during MR-guided SBRT was assessed.
A 3D cine MRI sequence was developed for fast, time-resolved 4D imaging, featuring a low spatial resolution that allows for rapid volumetric imaging at 430 ms. The 3D cines were acquired during the entire beam-on time of 23 fractions of online adaptive MR-guided SBRT for pancreatic tumors on a 1.5 T MR-Linac. A 3D deformation vector field (DVF) was extracted for every cine dynamic using deformable image registration. Next, these DVFs were used to warp the partial dose delivered in the time interval between consecutive cine acquisitions. The warped dose plans were summed to obtain a total delivered dose. The delivered dose was also calculated under various motion correction strategies. Key DVH parameters of the GTV, duodenum, small bowel and stomach were extracted from the delivered dose and compared to the planned dose. The uncertainty of the calculated DVFs was determined with the inverse consistency error (ICE) in the high-dose regions.
The mean (SD) relative (ratio delivered/planned) D of the GTV was 0.94 (0.06), and the mean (SD) relative D of the duodenum, small bowel, and stomach were respectively 0.98 (0.04), 1.00 (0.07), and 0.98 (0.06). In the fractions with the lowest delivered tumor coverage, it was found that significant lateral drifts had occurred. The DVFs used for dose warping had a low uncertainty with a mean (SD) ICE of 0.65 (0.07) mm.
We employed a fast, real-time 3D cine MRI sequence for dose reconstruction in the upper abdomen, and demonstrated that accurate DVFs, acquired directly from these images, can be used for dose warping. The reconstructed delivered dose showed only a modest degradation of tumor coverage, mostly attainable to baseline drifts. This emphasizes the need for motion monitoring and development of intrafraction treatment adaptation solutions, such as baseline drift corrections.
在胰腺肿瘤的磁共振引导 SBRT 中，通常使用（交错的）二维电影 MRI 来监测分次内运动。然而，这些图像通常不能完全捕捉肿瘤周围的情况，并且运动可能会受到平面内运动的扭曲。本研究评估了高度加速的 3D 电影 MRI 重建磁共振引导 SBRT 中递送剂量的可行性。
开发了一种用于快速、时间分辨的 4D 成像的 3D 电影 MRI 序列，其空间分辨率较低，可在 430ms 内实现快速容积成像。在 1.5TMR-Linac 上对胰腺肿瘤进行在线自适应磁共振引导 SBRT 的 23 个分次的整个射束照射期间采集 3D 电影。使用变形图像配准从每个电影动态提取三维变形向量场（DVF）。接下来，使用这些 DVF 来扭曲在连续电影采集之间的时间间隔内递送的部分剂量。扭曲后的剂量计划相加以获得总递送剂量。还根据各种运动校正策略计算了递送剂量。从递送剂量中提取了 GTV、十二指肠、小肠和胃的关键剂量体积直方图（DVH）参数，并与计划剂量进行了比较。在高剂量区域使用逆一致性误差（ICE）确定计算出的 DVF 的不确定性。
GTV 的平均（SD）相对（递送/计划）D 为 0.94（0.06），十二指肠、小肠和胃的平均（SD）相对 D 分别为 0.98（0.04）、1.00（0.07）和 0.98（0.06）。在肿瘤覆盖率最低的分次中，发现发生了明显的横向漂移。用于剂量扭曲的 DVF 具有较低的不确定性，平均（SD）ICE 为 0.65（0.07）mm。
我们使用快速、实时的 3D 电影 MRI 序列在上腹部进行剂量重建，并证明可以直接从这些图像中获取准确的 DVF 用于剂量扭曲。重建的递送剂量仅显示肿瘤覆盖率略有下降，主要归因于基线漂移。这强调了需要进行运动监测和开发分次内治疗自适应解决方案，例如基线漂移校正。
