Department of Clinical Research, University of Southern Denmark, Winsløwparken 19 3. Sal, 5000, Odense C, Denmark.
Laboratory of Radiation Physics, Department of Oncology, Odense University Hospital, Kløvervænget 19, Indgang 85, Pavillion, Stuen, 5000, Odense C, Denmark.
Radiat Oncol. 2020 Feb 7;15(1):32. doi: 10.1186/s13014-020-1482-y.
In this study we have evaluated the accuracy of automatic, deformable structure propagation from planning CT and MR scans for daily online plan adaptation for MR linac (MRL) treatment, which is an important element to minimize re-planning time and reduce the risk of misrepresenting the target due to this time pressure.
For 12 high-risk prostate cancer patients treated to the prostate and pelvic lymph nodes, target structures and organs at risk were delineated on both planning MR and CT scans and propagated using deformable registration to three T2 weighted MR scans acquired during the treatment course. Generated structures were evaluated against manual delineations on the repeated scans using intra-observer variation obtained on the planning MR as ground truth.
MR-to-MR propagated structures had significant less median surface distance and larger Dice similarity index compared to CT-MR propagation. The MR-MR propagation uncertainty was similar in magnitude to the intra-observer variation. Visual inspection of the deformed structures revealed that small anatomical differences between organs in source and destination image sets were generally well accounted for while large differences were not.
Both CT and MR based propagations require manual editing, but the current results show that MR-to-MR propagated structures require fewer corrections for high risk prostate cancer patients treated at a high-field MRL.
在这项研究中，我们评估了从计划 CT 和 MR 扫描自动、可变形结构传播的准确性，以便对 MR 直线加速器（MRL）治疗进行日常在线计划适应，这是最小化重新计划时间和降低由于时间压力而导致目标表示不准确的风险的重要因素。
对 12 例高危前列腺癌患者进行了治疗，包括前列腺和盆腔淋巴结，在计划 MR 和 CT 扫描上对靶区结构和危及器官进行了描绘，并使用可变形配准将其传播到治疗过程中获得的三个 T2 加权 MR 扫描中。使用在计划 MR 上获得的观察者内变异性作为金标准，对生成的结构在重复扫描上的手动描绘进行评估。
与 CT-MR 传播相比，MR-MR 传播的结构具有显著更小的中位表面距离和更大的 Dice 相似性指数。MR-MR 传播的不确定性与观察者内变异性的大小相似。对变形结构的视觉检查表明，源图像集和目标图像集中器官之间的小解剖差异通常可以很好地解释，而大的差异则不能很好地解释。
CT 和 MR 两种方法的传播都需要手动编辑，但目前的结果表明，对于在高场强 MRL 治疗的高危前列腺癌患者，MR-MR 传播的结构需要更少的修正。
