Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.
Int J Radiat Oncol Biol Phys. 2013 May 1;86(1):190-7. doi: 10.1016/j.ijrobp.2012.12.017. Epub 2013 Feb 12.
To investigate the time-resolved 3-dimensional (3D) internal motion throughout stereotactic body radiation therapy (SBRT) of tumors in the liver using standard x-ray imagers of a conventional linear accelerator.
Ten patients with implanted gold markers received 11 treatment courses of 3-fraction SBRT in a stereotactic body-frame on a conventional linear accelerator. Two pretreatment and 1 posttreatment cone-beam computed tomography (CBCT) scans were acquired during each fraction. The CBCT projection images were used to estimate the internal 3D marker motion during CBCT acquisition with 11-Hz resolution by a monoscopic probability-based method. Throughout the treatment delivery by conformal or volumetric modulated arc fields, simultaneous MV portal imaging (8 Hz) and orthogonal kV imaging (5 Hz) were applied to determine the 3D marker motion using either MV/kV triangulation or the monoscopic method when marker segmentation was unachievable in either MV or kV images. The accuracy of monoscopic motion estimation was quantified by also applying monoscopic estimation as a test for all treatments during which MV/kV triangulation was possible.
Root-mean-square deviations between monoscopic estimations and triangulations were less than 1.0 mm. The mean 3D intrafraction and intrafield motion ranges during liver SBRT were 17.6 mm (range, 5.6-39.5 mm) and 11.3 mm (2.1-35.5mm), respectively. The risk of large intrafraction baseline shifts correlated with intrafield respiratory motion range. The mean 3D intrafractional marker displacement relative to the first CBCT was 3.4 mm (range, 0.7-14.5 mm). The 3D displacements exceeded 8.8 mm 10% of the time.
Highly detailed time-resolved internal 3D motion was determined throughout liver SBRT using standard imaging equipment. Considerable intrafraction motion was observed. The demonstrated methods provide a widely available approach for motion monitoring that, combined with motion-adaptive treatment techniques, has the potential to improve the accuracy of radiation therapy for moving targets.
使用常规线性加速器的标准 X 射线成像仪，研究肝脏立体定向体部放射治疗（SBRT）中肿瘤的三维（3D）内部运动的时间分辨。
十名植入金标记的患者在常规线性加速器上的立体定向体架中接受了 3 分次 SBRT 的 11 个疗程。每次分割时都进行两次预处理和 1 次后处理锥形束 CT（CBCT）扫描。通过单目基于概率的方法，使用 CBCT 投影图像以 11Hz 的分辨率估计 CBCT 采集过程中的内部 3D 标记运动。在适形或容积调制弧形场的整个治疗过程中，应用同步 MV 门控成像（8Hz）和正交 kV 成像（5Hz），通过 MV/kV 三角测量或在 MV 或 kV 图像中无法进行标记分割时使用单目方法，确定 3D 标记运动。通过在可能进行 MV/kV 三角测量的所有治疗中也应用单目估计作为测试，量化单目运动估计的准确性。
单目估计与三角测量之间的均方根偏差小于 1.0mm。在肝脏 SBRT 期间，17.6mm（范围，5.6-39.5mm）和 11.3mm（2.1-35.5mm）分别为 17.6mm（范围，5.6-39.5mm）和 11.3mm（2.1-35.5mm）的分次内和场内运动范围。大的分次内基线偏移的风险与场内呼吸运动范围相关。与首次 CBCT 相比，标记的平均 3D 分次内位移为 3.4mm（范围，0.7-14.5mm）。3D 位移超过 8.8mm 的时间占 10%。
使用标准成像设备在整个肝脏 SBRT 过程中确定了高度详细的时间分辨内部 3D 运动。观察到相当大的分次内运动。所展示的方法为运动监测提供了一种广泛可用的方法，结合运动自适应治疗技术，有可能提高移动靶区放射治疗的准确性。
