Motion mitigation strategies are crucial for scanned particle therapy of mobile tumours in order to prevent geometrical target miss and interplay effects. We developed a patient-specific respiratory motion model based on simultaneously acquired time-resolved volumetric MRI and 2D abdominal ultrasound images. We present its effects on 4D pencil beam scanned treatment planning and simulated dose distributions. Given an ultrasound image of the liver and the diaphragm, principal component analysis and Gaussian process regression were applied to infer dense motion information of the lungs. 4D dose calculations for scanned proton therapy were performed using the estimated and the corresponding ground truth respiratory motion; the differences were compared by dose difference volume metrics. We performed this simulation study on 10 combined CT and 4DMRI data sets where the motion characteristics were extracted from 5 healthy volunteers and fused with the anatomical CT data of two lung cancer patients. Median geometrical estimation errors below 2 mm for all data sets and maximum dose differences of = 43.2% and = 16.3% were found. Moreover, it was shown that abdominal ultrasound imaging allows to monitor organ drift. This study demonstrated the feasibility of the proposed ultrasound-based motion modelling approach for its application in scanned proton therapy of lung tumours.

缓解运动的策略对于移动肿瘤的扫描粒子治疗至关重要，以防止几何目标丢失和相互作用。我们基于同时获取的时间分辨体积MRI和2D腹部超声图像，开发了针对患者的呼吸运动模型。我们介绍了其对4D铅笔束扫描治疗计划和模拟剂量分布的影响。给定肝脏和隔膜的超声图像，应用主成分分析和高斯过程回归来推断肺的密集运动信息。使用估计的和相应的地面真相呼吸运动进行扫描质子治疗的4D剂量计算；通过剂量差异量指标比较差异。我们对10个CT和4DMRI组合数据集进行了此模拟研究，其中从5名健康志愿者中提取了运动特征，并将其与两名肺癌患者的解剖CT数据融合在一起。所有数据集的中值几何估计误差低于2 mm，最大剂量差为发现＝ 43.2％和＝ 16.3％。此外，已表明腹部超声成像可以监测器官漂移。这项研究证明了所提出的基于超声的运动建模方法在肺肿瘤扫描质子治疗中的可行性。