Bylund Kevin C, Bayouth John E, Smith Mark C, Hass A Curtis, Bhatia Sudershan K, Buatti John M
Department of Radiation Oncology, University of Iowa, Iowa City, IA, USA.
Int J Radiat Oncol Biol Phys. 2008 Nov 1;72(3):949-56. doi: 10.1016/j.ijrobp.2008.07.002.
Determine the degree of interfraction prostate motion and its components measured by using daily megavoltage (MV) cone beam computed tomography (CBCT) imaging.
A total of 984 daily MV CBCT images from 24 patients undergoing definitive intensity-modulated radiotherapy for localized prostate cancer were analyzed retrospectively. Pretreatment couch shifts, based on physician registration of MV CBCT to planning CT data sets, were used as a measure of daily interfraction motion. Off-line bony registration was performed to separate bony misalignment from internal organ motion. Interobserver and intraobserver variation studies were performed on 20 MV CBCT images.
Mean interfraction prostate motion was 6.7 mm, with the greatest single-axis deviation in the anterior-posterior (AP) direction. The largest positional inaccuracy was accounted for by systematic deviations in bony misalignment, whereas random deviations occurred from bony misalignment and internal prostate motion. In the aggregate, AP motion did not correlate with days elapsed since beginning therapy or on average with rectal size at treatment planning. Interobserver variation was greatest in the AP direction, decreased in experienced observers, and further decreased in intraobserver studies. Mean interfraction motion during the first 6 days of therapy, when used as a subsequent offset, reduced acceptable AP planning target volume margins by 50%.
The MV CBCT is a practical direct method of daily localization that shows significant interfraction motion with respect to conventional three-dimensional conformal and intensity-modulated radiotherapy margins, similar to that measured in other modalities.
确定通过每日兆伏（MV）锥形束计算机断层扫描（CBCT）成像测量的分次间前列腺运动程度及其组成部分。
回顾性分析了24例接受局限性前列腺癌根治性调强放疗患者的984张每日MV CBCT图像。基于将MV CBCT与计划CT数据集进行医生配准的治疗前治疗床移位，用作每日分次间运动的度量。进行离线骨配准以将骨错位与内部器官运动区分开。对20张MV CBCT图像进行了观察者间和观察者内变异研究。
分次间前列腺平均运动为6.7毫米，在前后（AP）方向上的单轴偏差最大。最大的位置误差是由骨错位的系统偏差引起的，而随机偏差则来自骨错位和前列腺内部运动。总体而言，AP运动与开始治疗后的天数或治疗计划时的直肠大小平均值均无相关性。观察者间变异在AP方向上最大，在经验丰富的观察者中减小，在观察者内研究中进一步减小。治疗前6天的分次间平均运动用作后续偏移量时，可接受的AP计划靶体积边缘减少了50％。
MV CBCT是一种实用的每日定位直接方法，相对于传统的三维适形和调强放疗边缘，显示出明显的分次间运动，类似于在其他模式中测量的运动。
