Department of Radiation Oncology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California.
Department of Radiation Oncology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California.
Int J Radiat Oncol Biol Phys. 2018 Nov 15;102(4):885-894. doi: 10.1016/j.ijrobp.2018.05.012. Epub 2018 May 14.
To develop and validate a technique for radiation therapy gating using slow (≤1 frame per second) magnetic resonance imaging (MRI) and a motion model. Proposed uses of the technique include radiation therapy gating using T2-weighted images and conducting additional imaging studies during gated treatments.
The technique uses a physiologically guided breathing motion model to interpolate deformed target position between 2-dimensional (2D) MRI images acquired every 1 to 3 seconds. The model is parameterized by a 1-dimensional respiratory bellows surrogate and is continuously updated with the most recently acquired 2D images. A phantom and 8 volunteers were imaged with a 0.35T MRI-guided radiation therapy system. A balanced steady-state free precession sequence with a 2D frame rate of 3 frames per second was used to evaluate the technique. The accuracy and beam-on positive predictive value (PPV) of the model-based gating decisions were evaluated using the gating decisions derived from imaging as a ground truth. A T2-weighted gating offline proof-of-concept study using a half-Fourier, single-shot, turbo-spin echo sequence is reported.
Model-interpolated gating accuracy, beam-on PPV, and median absolute distances between model and image-tracked target centroids were, on average, 98.3%, 98.4%, and 0.33 mm, respectively, in the balanced steady-state free precession phantom studies and 93.7%, 92.1%, and 0.86 mm, respectively, in the volunteer studies. T2 model-interpolated gating in 6 volunteers yielded an average accuracy and PPV of 94.3% and 92.5%, respectively, and the mean absolute median distance between modeled and imaged target centroids was 0.86 mm.
This work demonstrates the concept of model-interpolated gating for MRI-guided radiation therapy. The technique was found to be potentially sufficiently accurate for clinical use. Further development is needed to accommodate out-of-plane motion and the use of an internal MR-based respiratory surrogate.
开发并验证一种使用慢速（每秒≤1 帧）磁共振成像（MRI）和运动模型的放射治疗门控技术。该技术的拟议用途包括使用 T2 加权图像进行放射治疗门控，并在门控治疗期间进行额外的成像研究。
该技术使用生理引导的呼吸运动模型，在每秒 1 到 3 秒采集的二维（2D）MRI 图像之间内插变形目标位置。该模型由一维呼吸波纹管替代物参数化，并使用最新采集的 2D 图像进行连续更新。使用 0.35T MRI 引导放射治疗系统对一个体模和 8 名志愿者进行了成像。使用具有每秒 3 帧的 2D 帧率的平衡稳态自由进动序列来评估该技术。使用源自成像的门控决策作为基准，评估基于模型的门控决策的准确性和射束导通阳性预测值（PPV）。报告了使用半傅里叶、单次激发、涡轮回波序列的 T2 加权门控离线概念验证研究。
在平衡稳态自由进动体模研究中，模型插值门控精度、射束导通 PPV 和模型与图像跟踪目标质心之间的中位数绝对距离平均分别为 98.3%、98.4%和 0.33 毫米，在志愿者研究中分别为 93.7%、92.1%和 0.86 毫米。在 6 名志愿者中进行的 T2 模型插值门控产生了平均精度和 PPV 分别为 94.3%和 92.5%，以及模型和成像目标质心之间的平均绝对中位数距离为 0.86 毫米。
这项工作证明了用于 MRI 引导放射治疗的模型插值门控的概念。该技术被发现具有足够的临床应用准确性。需要进一步开发以适应离轴运动和使用基于内部 MRI 的呼吸替代物。
