Department of Radiation Oncology, Stanford University, Stanford, California 94305, USA.
Int J Radiat Oncol Biol Phys. 2013 Jul 15;86(4):762-8. doi: 10.1016/j.ijrobp.2013.03.007. Epub 2013 Apr 19.
To assess the prostate intrafraction motion in volumetric modulated arc therapy treatments using cine megavoltage (MV) images acquired with an electronic portal imaging device (EPID).
Ten prostate cancer patients were treated with volumetric modulated arc therapy using a Varian TrueBeam linear accelerator equipped with an EPID for acquiring cine MV images during treatment. Cine MV images acquisition was scheduled for single or multiple treatment fractions (between 1 and 8). A novel automatic fiducial detection algorithm that can handle irregular multileaf collimator apertures, field edges, fast leaf and gantry movement, and MV image noise and artifacts in patient anatomy was used. All sets of images (approximately 25,000 images in total) were analyzed to measure the positioning accuracy of implanted fiducial markers and assess the prostate movement.
Prostate motion can vary greatly in magnitude among different patients. Different motion patterns were identified, showing its unpredictability. The mean displacement and standard deviation of the intrafraction motion was generally less than 2.0 ± 2.0 mm in each of the spatial directions. In certain patients, however, the percentage of the treatment time in which the prostate is displaced more than 5 mm from its planned position in at least 1 spatial direction was 10% or more. The maximum prostate displacement observed was 13.3 mm.
Prostate tracking and motion assessment was performed with MV imaging and an EPID. The amount of prostate motion observed suggests that patients will benefit from its real-time monitoring. Megavoltage imaging can provide the basis for real-time prostate tracking using conventional linear accelerators.
使用电子射野影像装置（EPID）获取的电影兆伏（MV）图像评估容积调强弧形治疗中的前列腺分次内运动。
10 例前列腺癌患者接受容积调强弧形治疗，使用配备 EPID 的瓦里安 TrueBeam 直线加速器在治疗期间获取电影 MV 图像。电影 MV 图像采集计划用于单次或多次治疗分次（1 至 8 次之间）。使用一种新的自动基准点检测算法，可以处理不规则多叶准直器孔径、射野边缘、快速叶片和龙门运动以及患者解剖结构中的 MV 图像噪声和伪影。分析了所有图像集（总共约 25000 张图像），以测量植入基准标记的定位准确性并评估前列腺运动。
不同患者的前列腺运动幅度差异很大。确定了不同的运动模式，表明其不可预测性。在每个空间方向上，分次内运动的平均位移和标准偏差通常小于 2.0±2.0mm。然而，在某些患者中，前列腺在至少 1 个空间方向上从计划位置位移超过 5mm 的治疗时间百分比为 10%或更高。观察到的最大前列腺位移为 13.3mm。
使用 MV 成像和 EPID 进行了前列腺跟踪和运动评估。观察到的前列腺运动量表明患者将受益于实时监测。兆伏成像可以为使用传统直线加速器进行实时前列腺跟踪提供基础。
