背景:胃肠道(GI)运动是腹部目标放射治疗中分数内/分数间变异性和不确定性的主要来源之一。胃肠道运动模型可以改善对递送剂量的评估,并有助于发育,测试,并验证了可变形图像配准(DIR)和剂量累积算法。
目的:在人体解剖学的4D扩展心脏躯干(XCAT)数字体模中实现胃肠道运动。
方法:根据文献研究确定了胃肠道直径大幅度变化的运动模式,并且可能在时间尺度上持续存在,与在线自适应计划和放射治疗相当。搜索标准包括比计划风险容量扩展更大的幅度变化和数十分钟量级的持续时间。确定了以下模式:蠕动,有节奏的分割,高振幅传播收缩(HAPCs),和强直收缩。通过行进和站立的正弦波对蠕动和有节奏的分段进行建模。HAPC和强直收缩通过行进和平稳高斯波来建模。在时间和空间域的波频散是通过线性实现的,指数,和逆幂律函数。建模函数应用于参考XCAT库中定义的非均匀有理B样条曲面的控制点。GI运动与标准4D-XCAT体模中可用的心脏和呼吸运动相结合。默认模型参数是根据对10例接受1.5TMR直线加速器治疗的患者的电影MRI采集分析估算的。
结果:我们证明了生成逼真的4D多模态图像的能力,这些图像模拟了胃肠道运动并结合了呼吸和心脏运动。所有的运动模式,除了强直收缩,在我们的电影核磁共振成像采集分析中观察到。蠕动是最常见的。从电影MRI估计的默认参数用作模拟实验的初始值。结果表明,在接受立体定向放射治疗腹部目标的患者中,胃肠运动的影响可以与呼吸运动的影响相当或更大。
结论:数字体模提供了逼真的模型来帮助医学成像和放射治疗研究。胃肠运动性的增加将进一步促进发展,测试,磁共振引导放疗的DIR和剂量累积算法的验证。本文受版权保护。保留所有权利。
BACKGROUND: Gastrointestinal (GI) tract motility is one of the main sources for intra/inter-fraction variability and uncertainty in radiation therapy for abdominal targets. Models for GI motility can improve the assessment of delivered dose and contribute to the development, testing, and validation of deformable image registration (DIR) and dose-accumulation algorithms.
OBJECTIVE: To implement GI tract motion in the 4D extended cardiac-torso (XCAT) digital phantom of human anatomy.
METHODS: Motility modes that exhibit large amplitude changes in the diameter of the GI tract and may persist over timescales comparable to online adaptive planning and radiotherapy delivery were identified based on literature research. Search criteria included amplitude changes larger than planning risk volume expansions and durations of the order of tens of minutes. The following modes were identified: peristalsis, rhythmic segmentation, high amplitude propagating contractions (HAPCs), and tonic contractions. Peristalsis and rhythmic segmentations were modeled by traveling and standing sinusoidal waves. HAPCs and tonic contractions were modeled by traveling and stationary Gaussian waves. Wave dispersion in the temporal and spatial domain was implemented by linear, exponential, and inverse power law functions. Modeling functions were applied to the control points of the nonuniform rational B-spline surfaces defined in the reference XCAT library. GI motility was combined with the cardiac and respiratory motions available in the standard 4D-XCAT phantom. Default model parameters were estimated based on the analysis of cine MRI acquisitions in 10 patients treated in a 1.5T MR-linac.
RESULTS: We demonstrate the ability to generate realistic 4D multimodal images that simulate GI motility combined with respiratory and cardiac motion. All modes of motility, except tonic contractions, were observed in the analysis of our cine MRI acquisitions. Peristalsis was the most common. Default parameters estimated from cine MRI were used as initial values for simulation experiments. It is shown that in patients undergoing stereotactic body radiotherapy for abdominal targets, the effects of GI motility can be comparable or larger than the effects of respiratory motion.
CONCLUSIONS: The digital phantom provides realistic models to aid in medical imaging and radiation therapy research. The addition of GI motility will further contribute to the development, testing, and validation of DIR and dose accumulation algorithms for MR-guided radiotherapy.