Grimbergen Guus, Eijkelenkamp Hidde, van Vulpen Jonna K, van de Ven Saskia, Raaymakers Bas W, Intven Martijn P W, Meijer Gert J
Department of Radiation Oncology, University Medical Center Utrecht, the Netherlands.
Phys Imaging Radiat Oncol. 2023 Mar 25;26:100434. doi: 10.1016/j.phro.2023.100434. eCollection 2023 Apr.
Online adaptive magnetic resonance (MR)-guided treatment planning for pancreatic tumors on 1.5T systems typically employs Cartesian 3D w magnetic resonance imaging (MRI). The main disadvantage of this sequence is that respiratory motion results in substantial blurring in the abdomen, which can hamper delineation accuracy. This study investigated the use of two motion-robust radial MRI sequences as main delineation scan for pancreatic MR-guided radiotherapy.
Twelve patients with pancreatic tumors were imaged with a 3D w scan, a Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER) scan (partially overlapping strips), and a 3D Vane scan (stack-of-stars), on a 1.5T MR-Linac under abdominal compression. The scans were assessed by three radiation oncologists for their suitability for online adaptive delineation. A quantitative comparison was made for gradient entropy and the effect of motion on apparent target position.
The PROPELLER scans were selected as first preference in 56% of the cases, the 3D w in 42% and the 3D Vane in 3%. PROPELLER scans sometimes contained a large interslice variation which would have compromised delineation. Gradient entropy was significantly higher in 3D w patient scans. The apparent target position was more sensitive to motion amplitude in the PROPELLER scans, but substantial offsets did not occur under 10 mm peak-to-peak.
PROPELLER MRI may be a superior imaging sequence for pancreatic MRgRT compared to standard Cartesian sequences. The large interslice variation should be mitigated through further sequence optimization before PROPELLER can be adopted for online treatment adaptation.
在1.5T系统上对胰腺肿瘤进行在线自适应磁共振（MR）引导的治疗计划通常采用笛卡尔三维加权磁共振成像（MRI）。该序列的主要缺点是呼吸运动会导致腹部出现明显模糊，这可能会妨碍勾画的准确性。本研究调查了使用两种运动稳健的径向MRI序列作为胰腺MR引导放疗的主要勾画扫描序列。
12例胰腺肿瘤患者在1.5T MR直线加速器下腹部加压的情况下，分别进行了三维加权扫描、周期性旋转重叠平行线增强重建（PROPELLER）扫描（部分重叠条带）和三维叶片扫描（星状堆叠）。三位放射肿瘤学家对这些扫描进行了评估，以确定其是否适合在线自适应勾画。对梯度熵以及运动对表观靶位置的影响进行了定量比较。
在56%的病例中，PROPELLER扫描被选为首选，三维加权扫描为42%，三维叶片扫描为3%。PROPELLER扫描有时包含较大的层间差异，这可能会影响勾画。三维加权患者扫描中的梯度熵显著更高。在PROPELLER扫描中，表观靶位置对运动幅度更敏感，但在峰峰值小于10mm时不会出现明显偏移。
与标准笛卡尔序列相比，PROPELLER MRI可能是胰腺MRgRT的一种更优成像序列。在将PROPELLER用于在线治疗适应性之前，应通过进一步的序列优化来减轻较大的层间差异。
