Division of Medical Radiation Physics, Department of Radiation Oncology, Medical University of Vienna, Vienna, Austria.
Division of Medical Radiation Physics, Department of Radiation Oncology, Medical University of Vienna, Vienna, Austria.
Z Med Phys. 2021 Feb;31(1):78-88. doi: 10.1016/j.zemedi.2020.10.004. Epub 2021 Jan 15.
Recent developments on synthetically generated CTs (sCT), hybrid MRI linacs and MR-only simulations underlined the clinical feasibility and acceptance of MR guided radiation therapy. However, considering clinical application of open and low field MR with a limited field of view can result in truncation of the patient's anatomy which further affects the MR to sCT conversion. In this study an acquisition protocol and subsequent MR image stitching is proposed to overcome the limited field of view restriction of open MR scanners, for MR-only photon and proton therapy.
12 prostate cancer patients scanned with an open 0.35T scanner were included. To obtain the full body contour an enhanced imaging protocol including two repeated scans after bilateral table movement was introduced. All required structures (patient contour, target and organ at risk) were delineated on a post-processed combined transversal image set (stitched MRI). The postprocessed MR was converted into a sCT by a pretrained neural network generator. Inversely planned photon and proton plans (VMAT and SFUD) were designed using the sCT and recalculated for rigidly and deformably registered CT images and compared based on D2%, D50%, V70Gy for organs at risk and based on D2%, D50%, D98% for the CTV and PTV. The stitched MRI and the untruncated MRI were compared to the CT, and the maximum surface distance was calculated. The sCT was evaluated with respect to delineation accuracy by comparing on stitched MRI and sCT using the DICE coefficient for femoral bones and the whole body.
Maximum surface distance analysis revealed uncertainties in lateral direction of 1-3mm on average. DICE coefficient analysis confirms good performance of the sCT conversion, i.e. 92%, 93%, and 100% were obtained for femoral bone left and right and whole body. Dose comparison resulted in uncertainties below 1% between deformed CT and sCT and below 2% between rigidly registered CT and sCT in the CTV for photon and proton treatment plans.
A newly developed acquisition protocol for open MR scanners and subsequent Sct generation revealed good acceptance for photon and proton therapy. Moreover, this protocol tackles the restriction of the limited FOVs and expands the capacities towards MR guided proton therapy with horizontal beam lines.
最近在合成 CT（sCT）、混合 MRI 直线加速器和仅 MRI 模拟方面的进展强调了 MR 引导放射治疗的临床可行性和可接受性。然而，考虑到具有有限视野的开放式和低场 MR 的临床应用可能导致患者解剖结构的截断，这进一步影响了 MR 到 sCT 的转换。在这项研究中，提出了一种采集协议和随后的 MR 图像拼接，以克服开放式 MR 扫描仪的有限视野限制，用于仅 MR 光子和质子治疗。
纳入了 12 例前列腺癌患者，这些患者均使用开放式 0.35T 扫描仪进行扫描。为了获得完整的身体轮廓，引入了一种增强成像协议，包括在双侧工作台移动后重复两次扫描。所有需要的结构（患者轮廓、靶区和危及器官）均在经过后处理的横向图像集（拼接 MRI）上进行描绘。将经过后处理的 MR 通过预先训练的神经网络生成器转换为 sCT。使用 sCT 设计反向计划的光子和质子计划（VMAT 和 SFUD），并针对刚性和可变形注册的 CT 图像进行重新计算，并根据危及器官的 D2%、D50%、V70Gy 以及根据 CTV 和 PTV 的 D2%、D50%、D98%进行比较。将拼接 MRI 与未截断的 MRI 与 CT 进行比较，并计算最大表面距离。使用股骨的 DICE 系数和整个身体的 DICE 系数，通过在拼接 MRI 和 sCT 上进行比较来评估 sCT 的勾画准确性。
最大表面距离分析显示，平均侧向不确定性为 1-3mm。DICE 系数分析证实了 sCT 转换的良好性能，即左股骨和右股骨以及整个身体分别获得了 92%、93%和 100%。光子和质子治疗计划中，变形 CT 和 sCT 之间的不确定性低于 1%，刚性注册 CT 和 sCT 之间的不确定性低于 2%。
为开放式 MR 扫描仪开发的新采集协议和随后的 sCT 生成，为光子和质子治疗提供了良好的接受度。此外，该协议解决了有限 FOV 的限制，并为具有水平射束线的 MR 引导质子治疗扩展了能力。
