Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
Int J Radiat Oncol Biol Phys. 2012 May 1;83(1):400-7. doi: 10.1016/j.ijrobp.2011.05.049. Epub 2011 Oct 20.
When one is performing online setup correction for prostate positioning displacements prior to daily dose delivery, intrafraction motion can become a limiting factor to prostate targeting accuracy. The aim of this study was to quantify and characterize prostate intrafraction motion assessed by multiple kilovoltage (kV) and megavoltage (MV) imaging of implanted markers during treatment in a large patient group.
Intrafraction motion in the sagittal plane was studied by retrospective analysis of displacements of implanted gold markers on (nearly) lateral kV and MV images obtained at various time points during the treatment fractions (mean, 27 per patient) in 108 consecutive patients. The effective prostate motion in a fraction was defined as the time-weighted mean displacement.
Prostate displacements in the sagittal plane increased during the fraction (mean, 0.2 ± 0.2 mm/min). Forty percent of patients had a systematic (i.e., appearing in all fractions) effective displacement in the sagittal plane greater than 2 mm. Observed effective population mean-of-means (μeff) +/- systematic (Σeff) intrafraction motion (μ(eff) ± Σ(eff)) was 0.9 ± 1.1 mm and 0.6 ± 1.0 mm for the anterior-posterior and superior inferior directions, respectively. Corresponding random motion (σ(eff)) was 1.2 mm and 1.1 mm. Mean effective prostate motion in the first 5 fractions was predictive for mean effective displacement in the remaining fractions (p < 0.001).
For a large subgroup of patients, the systematic component of intrafraction prostate motion was substantial. Intrafraction motion correction prior to each beam delivery or offline corrections could likely be beneficial for the subgroup of patients with significant motion. The systematic component is well predicted by measurements in the initial fractions.
在每日剂量输送前对前列腺定位位移进行在线设置校正时，分次内运动可能成为前列腺靶区准确性的限制因素。本研究的目的是量化和描述在 108 例连续患者的治疗过程中，通过植入标记物的多次千伏（kV）和兆伏（MV）成像评估的前列腺分次内运动，并对其进行特征描述。
通过对治疗过程中各个时间点（每个患者平均 27 个）获得的几乎侧向 kV 和 MV 图像上植入的金标记物的位移进行回顾性分析，研究矢状面内的分次内运动。在一个分数内的有效前列腺运动被定义为时间加权平均位移。
在治疗过程中，前列腺在矢状面内的位移增加（平均 0.2 ± 0.2 mm/min）。40%的患者在矢状面内的系统（即在所有分数中均出现）有效位移大于 2 毫米。观察到的有效群体均值（μeff）±系统（Σeff）分次内运动（μ（eff）±Σ（eff））分别为 0.9 ± 1.1 毫米和 0.6 ± 1.0 毫米，用于前-后和上-下方向。相应的随机运动（σeff）为 1.2 毫米和 1.1 毫米。前 5 个分数的平均有效前列腺运动可预测剩余分数的平均有效位移（p < 0.001）。
对于很大一部分患者，分次内前列腺运动的系统成分是相当大的。在每次光束输送前进行分次内运动校正或离线校正，可能对具有显著运动的患者亚组有益。系统成分可以通过初始分数中的测量值很好地预测。
