Grimbergen Guus, Eijkelenkamp Hidde, Heerkens Hanne D, Raaymakers Bas W, Intven Martijn P W, Meijer Gert J
Department of Radiation Oncology, University Medical Center Utrecht, the Netherlands.
Phys Imaging Radiat Oncol. 2021 Dec 21;21:1-5. doi: 10.1016/j.phro.2021.12.001. eCollection 2022 Jan.
Stereotactic body radiotherapy (SBRT) has been shown to be a promising therapy for unresectable pancreatic tumors. However, intrafraction motion, caused by respiratory motion and organ drift, is one of the main concerns for efficient dose delivery in ungated upper abdominal radiotherapy. The aim of this study was to analyze the intrafraction gross tumor volume (GTV) motion in a clinical cohort.
We included 13 patients that underwent online adaptive magnetic resonance (MR)-guided SBRT for malignancies in the pancreatic region (5 × 8 Gy). An abdominal corset was fitted in order to reduce the abdominal respiratory motion. Coronal and sagittal cine magnetic resonance images of the tumor region were made at 2 Hz during the entire beam-on time of each fraction. We used deformable image registration to obtain GTV motion profiles in all three directions, which were subsequently high-pass and low-pass filtered to isolate the motion caused by respiratory motion and baseline drift, respectively.
The mean (SD) respiratory amplitudes were 4.2 (1.9) mm cranio-caudal (CC), 2.3 (1.1) mm ventral-dorsal (AP) and 1.4 (0.6) mm left-right (LR), with low variability within patients. The mean (SD) maximum baseline drifts were 1.2 (1.1) mm CC, 0.5 (0.4) mm AP and 0.5 (0.3) mm LR. The mean (SD) minimum baseline drifts were -0.7 (0.5) mm CC, -0.6 (0.5) mm AP and -0.5 (0.4) mm LR.
Overall tumor motion during treatment was small and interfractionally stable. These findings show that high-precision ungated MR-guided SBRT is feasible with an abdominal corset.
立体定向体部放疗（SBRT）已被证明是治疗不可切除胰腺肿瘤的一种有前景的疗法。然而，由呼吸运动和器官漂移引起的分次内运动是无门控上腹部放疗中有效剂量递送的主要问题之一。本研究的目的是分析临床队列中的分次内大体肿瘤体积（GTV）运动。
我们纳入了13例接受在线自适应磁共振（MR）引导的胰腺区域恶性肿瘤SBRT（5×8 Gy）的患者。佩戴腹部束带来减少腹部呼吸运动。在每个分次的整个束流开启时间内，以2 Hz的频率采集肿瘤区域的冠状面和矢状面电影磁共振图像。我们使用可变形图像配准来获取所有三个方向上的GTV运动轮廓，随后分别进行高通和低通滤波，以分离由呼吸运动和基线漂移引起的运动。
平均（标准差）呼吸幅度在头足方向（CC）为4.2（1.9）mm，腹背方向（AP）为2.3（1.1）mm，左右方向（LR）为1.4（0.6）mm，患者内部的变异性较低。平均（标准差）最大基线漂移在CC方向为1.2（1.1）mm，AP方向为0.5（0.4）mm，LR方向为0.5（0.3）mm。平均（标准差）最小基线漂移在CC方向为 -0.7（0.5）mm，AP方向为 -0.6（0.5）mm，LR方向为 -0.5（0.4）mm。
治疗期间总体肿瘤运动较小且分次间稳定。这些发现表明，佩戴腹部束带进行高精度无门控MR引导的SBRT是可行的。
