Memorial Sloan Kettering Cancer Center, New York, NY, USA.
Department of Oncology and Radiotherapy & Department of Medical Physics, Turku University Hospital, Turku, Finland.
J Appl Clin Med Phys. 2021 Mar;22(3):207-215. doi: 10.1002/acm2.13205. Epub 2021 Feb 22.
To validate a synthetic computed tomography (sCT) software with continuous HUs and large field-of-view (FOV) coverage for magnetic resonance imaging (MRI)-only workflow of general pelvis anatomy in radiotherapy (RT).
An sCT software for general pelvis anatomy (prostate, rectum, and female pelvis) has been developed by Philips Healthcare and includes continuous HUs assignment along with large FOV coverage. General pelvis sCTs were generated using a two-stack T1-weighted mDixon fast-field echo (FFE) sequence with a superior-inferior coverage of 36 cm. Seventy-seven prostate, 43 rectum, and 27 gynecological cases were scanned by three different institutions. mDixon image quality and sCTs were evaluated for soft tissue contrast by using a confidence level scale from 1 to 5 for bladder, prostate/rectum interface, mesorectum, and fiducial maker visibility. Dosimetric comparison was performed by recalculating the RT plans on the sCT after rigid registration. For 12 randomly selected cases, the mean absolute error (MAE) between sCT and CT was calculated to evaluate HU similarity, and the Pearson correlation coefficients (PCC) between the CT- and sCT-generated digitally reconstructed radiographs (DRRs) were obtained for quantitative comparison. To examine geometric accuracy of sCT as a reference for cone beam CT (CBCT), the difference between bone-based alignment of CBCT to CT and CBCT to sCT was obtained for 19 online-acquired CBCTs from three patients.
Two-stack mDixon scans with large FOV did not show any image inhomogeneity or fat-water swap artifact. Fiducials, Foley catheter, and even rectal spacer were visible as dark signal on the sCT. Average visibility confidence level (average ± standard deviation) on the sCT was 5.0 ± 0.0, 4.6 ± 0.5, 3.8 ± 0.4, and 4.0 ± 1.1 for bladder, prostate/rectum interface, mesorectum and fiducial markers. Dosimetric accuracy showed on average < 1% difference with the CT-based plans for target and normal structures. The MAE of bone and soft tissue between the sCT and CT are 120.9 ± 15.4 HU, 33.4 ± 4.1 HU, respectively. Average PCC of all evaluated DRR pairs was 0.975. The average offset between CT and sCT as reference was (LR, AP, SI) = (0.19 ± 0.35, 0.14 ± 0.60, 0.44 ± 0.54) mm.
The continuous HU sCT software-generated realistic sCTs and DRRs to enable MRI-only planning for general pelvis anatomy.
验证一款适用于磁共振成像（MRI）仅流程的通用骨盆解剖学放疗的连续 Hounsfield 单位（HU）和大视场（FOV）覆盖范围的合成 CT（sCT）软件。
飞利浦医疗保健公司开发了一种用于通用骨盆解剖学（前列腺、直肠和女性骨盆）的 sCT 软件，它包括连续的 HU 赋值以及大 FOV 覆盖范围。使用上下覆盖范围为 36cm 的双堆叠 T1 加权 mDixon 快速场回波（FFE）序列生成通用骨盆 sCT。三个不同机构扫描了 77 例前列腺、43 例直肠和 27 例妇科病例。使用 1 到 5 的置信水平刻度评估 mDixon 图像质量和 sCT 的软组织对比度，用于膀胱、前列腺/直肠界面、直肠系膜和基准标记可视性。通过刚性配准后在 sCT 上重新计算放疗计划来进行剂量比较。对于 12 个随机选择的病例，计算 sCT 和 CT 之间的平均绝对误差（MAE），以评估 HU 相似性，并获得 CT 和 sCT 生成的数字重建射线照片（DRR）之间的 Pearson 相关系数（PCC），以进行定量比较。为了检查 sCT 的几何准确性作为锥形束 CT（CBCT）的参考，对于来自三个患者的 19 个在线采集的 CBCT，获取基于骨骼的 CBCT 与 CT 和 CBCT 与 sCT 的对准之间的差异。
具有大 FOV 的双堆叠 mDixon 扫描没有显示任何图像不均匀性或脂肪-水交换伪影。基准标记、 Foley 导管，甚至直肠间隔器在 sCT 上都显示为暗信号。sCT 上的平均可见性置信度（平均值±标准差）分别为膀胱 5.0±0.0、前列腺/直肠界面 4.6±0.5、直肠系膜 3.8±0.4 和基准标记 4.0±1.1。目标和正常结构的基于 CT 的计划的剂量准确性平均差异小于 1%。sCT 和 CT 之间的骨和软组织的 MAE 分别为 120.9±15.4HU 和 33.4±4.1HU。所有评估的 DRR 对的平均 PCC 为 0.975。以 CT 为参考的 sCT 的平均偏移量为（LR、AP、SI）=（0.19±0.35、0.14±0.60、0.44±0.54）mm。
连续 HU 的 sCT 软件生成了逼真的 sCT 和 DRR，可实现通用骨盆解剖学的 MRI 仅计划。
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