Department of Radiation Oncology, LMU University Hospital, LMU Munich, Munich, Germany.
Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy.
Phys Med Biol. 2023 Nov 28;68(23). doi: 10.1088/1361-6560/acf6f0.
To experimentally validate a method to create continuous time-resolved estimated synthetic 4D-computed tomography datasets (tresCTs) based on orthogonal cine MRI data for lung cancer treatments at a magnetic resonance imaging (MRI) guided linear accelerator (MR-linac).A breathing porcine lung phantom was scanned at a CT scanner and 0.35 T MR-linac. Orthogonal cine MRI series (sagittal/coronal orientation) at 7.3 Hz, intersecting tumor-mimicking gelatin nodules, were deformably registered to mid-exhale 3D-CT and 3D-MRI datasets. The time-resolved deformation vector fields were extrapolated to 3D and applied to a reference synthetic 3D-CT image (sCT), while accounting for breathing phase-dependent lung density variations, to create 82 s long tresCTs at 3.65 Hz. Ten tresCTs were created for ten tracked nodules with different motion patterns in two lungs. For each dataset, a treatment plan was created on the mid-exhale phase of a measured ground truth (GT) respiratory-correlated 4D-CT dataset with the tracked nodule as gross tumor volume (GTV). Each plan was recalculated on the GT 4D-CT, randomly sampled tresCT, and static sCTimages. Dose distributions for corresponding breathing phases were compared in gamma (2%/2 mm) and dose-volume histogram (DVH) parameter analyses.The mean gamma pass rate between all tresCT and GT 4D-CT dose distributions was 98.6%. The mean absolute relative deviations of the tresCT with respect to GT DVH parameters were 1.9%, 1.0%, and 1.4% for the GTV,, and, respectively, 1.0% for the remaining nodules, and 1.5% for the lung. The gamma pass rate for the tresCTs was significantly larger (< 0.01), and the GTVdeviations with respect to the GT were significantly smaller (< 0.01) than for the sCT.The results suggest that tresCTs could be valuable for time-resolved reconstruction and intrafractional accumulation of the dose to the GTV for lung cancer patients treated at MR-linacs in the future.
为了在磁共振引导线性加速器（MR-linac）上对肺癌治疗进行实验验证，基于正交电影 MRI 数据创建连续时间分辨估计合成 4D-计算机断层摄影术（tresCT）的方法。在 CT 扫描仪和 0.35T MR-linac 上对呼吸猪肺模型进行扫描。在 7.3Hz 时，与肿瘤模拟明胶结节交叉的正交电影 MRI 系列（矢状/冠状方向）可变形地注册到 mid-exhale 3D-CT 和 3D-MRI 数据集。时间分辨变形向量场被外推到 3D，并应用于参考合成 3D-CT 图像（sCT），同时考虑到呼吸相位相关的肺密度变化，以在 3.65Hz 时创建 82 秒长的 tresCTs。在两个肺中，对于具有不同运动模式的十个跟踪结节，创建了十个 tresCTs。对于每个数据集，在测量的与呼吸相关的 4D-CT 数据集的 mid-exhale 相位上创建了基于跟踪结节作为大体肿瘤体积（GTV）的治疗计划。每个计划都在 GT 4D-CT、随机采样的 tresCT 和静态 sCT 图像上重新计算。比较了相应呼吸相位的剂量分布伽马（2%/2mm）和剂量体积直方图（DVH）参数分析。所有 tresCT 和 GT 4D-CT 剂量分布之间的平均伽马通过率为 98.6%。tresCT 相对于 GT DVH 参数的平均绝对相对偏差分别为 1.9%、1.0%和 1.4%，GTV 分别为 1.0%，其余结节为 1.5%，肺为 1.5%。tresCT 的伽马通过率明显更大（<0.01），而 GTV 相对于 GT 的偏差明显更小（<0.01）。结果表明，tresCT 对于未来在 MR-linac 上治疗肺癌患者的 GTV 剂量的时间分辨重建和分次内积累可能具有重要价值。
