Department of Radiation Oncology, Leuven Cancer Institute, Belgium.
Radiother Oncol. 2011 Feb;98(2):181-6. doi: 10.1016/j.radonc.2010.12.019. Epub 2011 Feb 4.
Intrafractional motion consists of two components: (1) the movement between the on-line repositioning procedure and the treatment start and (2) the movement during the treatment delivery. The goal of this study is to estimate this intrafractional movement of the prostate during prostate cancer radiotherapy.
Twenty-seven patients with prostate cancer and implanted fiducials underwent a marker match procedure before a five-field IMRT treatment. For all fields, in-treatment images were obtained and then processed to enable automatic marker detection. Combining the subsequent projection images, five positions of each marker were determined using the shortest path approach. The residual set-up error (RSE) after kV-MV based prostate localization, the prostate position as a function of time during a radiotherapy session and the required margins to account for intrafractional motion were determined.
The mean RSE and standard deviation in the antero-posterior, cranio-caudal and left-right direction were 2.3±1.5 mm, 0.2±1.1 mm and -0.1±1.1 mm, respectively. Almost all motions occurred in the posterior direction before the first treatment beam as the percentage of excursions>5 mm was reduced significantly when the RSE was not accounted for. The required margins for intrafractional motion increased with prolongation of the treatment. Application of a repositioning protocol after every beam could decrease the 1cm margin from CTV to PTV by 2 mm.
The RSE is the main contributor to intrafractional motion. This RSE after on-line prostate localization and patient repositioning in the posterior direction emphasizes the need to speed up the marker match procedure. Also, a prostate IMRT treatment should be administered as fast as possible, to ensure that the pre-treatment repositioning efforts are not erased by intrafractional prostate motion. This warrants an optimized workflow with the use of faster treatment techniques.
分次内运动由两个部分组成：（1）在线重新定位过程与治疗开始之间的运动，以及（2）治疗过程中的运动。本研究的目的是估计前列腺癌放射治疗过程中前列腺的这种分次内运动。
27 例前列腺癌患者植入基准标记物，在五野调强放疗前进行了标记物匹配程序。对所有野，在治疗中获得图像，并进行处理以实现自动标记物检测。通过最短路径方法，结合随后的投影图像，确定每个标记物的五个位置。在基于千伏（kV）-兆伏（MV）的前列腺定位后，确定残余的摆位误差（RSE）、放疗过程中前列腺位置随时间的变化以及为补偿分次内运动所需的边界。
在前后、头脚和左右方向上，RSE 的平均值和标准差分别为 2.3±1.5mm、0.2±1.1mm 和-0.1±1.1mm。在第一束治疗射线之前，几乎所有的运动都发生在后方，因为当不考虑 RSE 时，超过 5mm 的运动幅度的百分比显著降低。分次内运动所需的边界随治疗时间的延长而增加。每次照射后应用重新定位方案可以将从 CTV 到 PTV 的 1cm 边界减少 2mm。
RSE 是分次内运动的主要贡献者。在线前列腺定位和患者在后方向上重新定位后的 RSE 强调需要加快标记物匹配过程。此外，前列腺调强放疗应尽快进行，以确保治疗前的重新定位努力不会因前列腺分次内运动而消除。这需要使用更快的治疗技术来优化工作流程。
