Stevens M Tynan R, Parsons Dave D, Robar James L
Department of Medical Physics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada and Nova Scotia Cancer Centre, QEII Health Science Centre, Halifax, Nova Scotia B3H 2Y9, Canada.
Med Phys. 2016 May;43(5):2558. doi: 10.1118/1.4947295.
To demonstrate continuous kV x-ray monitoring of prostate motion using both stereoscopic and monoscopic localizations, assess the spatial accuracy of these techniques, and evaluate the dose delivered from the added image guidance.
The authors implemented both stereoscopic and monoscopic fiducial localizations using a room-mounted dual oblique x-ray system. Recently developed monoscopic 3D position estimation techniques potentially overcome the issue of treatment head interference with stereoscopic imaging at certain gantry angles. To demonstrate continuous position monitoring, a gold fiducial marker was placed in an anthropomorphic phantom and placed on the Linac couch. The couch was used as a programmable translation stage. The couch was programmed with a series of patient prostate motion trajectories exemplifying five distinct categories: stable prostate, slow drift, persistent excursion, transient excursion, and high frequency excursions. The phantom and fiducial were imaged using 140 kVp, 0.63 mAs per image at 1 Hz for a 60 s monitoring period. Both stereoscopic and monoscopic 3D localization accuracies were assessed by comparison to the ground-truth obtained from the Linac log file. Imaging dose was also assessed, using optically stimulated luminescence dosimeter inserts in the phantom.
Stereoscopic localization accuracy varied between 0.13 ± 0.05 and 0.33 ± 0.30 mm, depending on the motion trajectory. Monoscopic localization accuracy varied from 0.2 ± 0.1 to 1.1 ± 0.7 mm. The largest localization errors were typically observed in the left-right direction. There were significant differences in accuracy between the two monoscopic views, but which view was better varied from trajectory to trajectory. The imaging dose was measured to be between 2 and 15 μGy/mAs, depending on location in the phantom.
The authors have demonstrated the first use of monoscopic localization for a room-mounted dual x-ray system. Three-dimensional position estimation from monoscopic imaging permits continuous, uninterrupted intrafraction motion monitoring even in the presence of gantry rotation, which may block kV sources or imagers. This potentially allows for more accurate treatment delivery, by ensuring that the prostate does not deviate substantially from the initial setup position.
使用立体定位和单视定位演示对前列腺运动进行连续千伏（kV）X射线监测，评估这些技术的空间准确性，并评估附加图像引导所输送的剂量。
作者使用安装在机房的双斜X射线系统实施了立体定位和单视基准定位。最近开发的单视三维位置估计技术有可能克服在某些机架角度治疗头对立体成像的干扰问题。为了演示连续位置监测，将一个金基准标记物放置在一个拟人化体模中，并放置在直线加速器治疗床上。治疗床用作可编程平移台。治疗床按照一系列患者前列腺运动轨迹进行编程，这些轨迹体现了五个不同类别：稳定的前列腺、缓慢漂移、持续偏移、短暂偏移和高频偏移。在60秒的监测期内，使用140 kVp、每幅图像0.63 mAs、1 Hz的频率对体模和基准进行成像。通过与从直线加速器日志文件获得的真实情况进行比较，评估立体定位和单视三维定位的准确性。还使用体模中的光激励发光剂量计插入物评估成像剂量。
立体定位准确性根据运动轨迹在0.13±0.05至0.33±0.30毫米之间变化。单视定位准确性在0.2±0.1至1.1±0.7毫米之间变化。最大的定位误差通常在左右方向上观察到。两个单视视图之间的准确性存在显著差异，但哪个视图更好因轨迹而异。成像剂量根据在体模中的位置测量为2至15 μGy/mAs。
作者首次展示了在安装在机房的双X射线系统中使用单视定位。单视成像的三维位置估计允许即使在存在机架旋转可能阻挡kV源或成像器的情况下进行连续、不间断的分次内运动监测。通过确保前列腺不会大幅偏离初始设置位置，这有可能实现更精确的治疗输送。
