School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
Int J Radiat Oncol Biol Phys. 2013 Mar 1;85(3):700-6. doi: 10.1016/j.ijrobp.2012.05.044. Epub 2012 Jul 12.
Correction for intrafraction prostate motion becomes important for hypofraction treatment of prostate cancer. The purpose of this study was to estimate an ideal planning margin to account for intrafraction prostate motion as a function of imaging and repositioning frequency in the absence of continuous prostate motion monitoring.
For 31 patients receiving intensity modulated radiation therapy treatment, prostate positions sampled at 10 Hz during treatment using the Calypso system were analyzed. Using these data, we simulated multiple, less frequent imaging protocols, including intervals of every 10, 15, 20, 30, 45, 60, 90, 120, 180, and 240 seconds. For each imaging protocol, the prostate displacement at the imaging time was corrected by subtracting prostate shifts from the subsequent displacements in that fraction. Furthermore, we conducted a principal component analysis to quantify the direction of prostate motion.
Averaging histograms of every 240 and 60 seconds for all patients, vector displacements of the prostate were, respectively, within 3 and 2 mm for 95% of the treatment time. A vector margin of 1 mm achieved 91.2% coverage of the prostate with 30 second imaging. The principal component analysis for all fractions showed the largest variance in prostate position in the midsagittal plane at 54° from the anterior direction, indicating that anterosuperior to inferoposterior is the direction of greatest motion. The smallest prostate motion is in the left-right direction.
The magnitudes of intrafraction prostate motion along the superior-inferior and anterior-posterior directions are comparable, and the smallest motion is in the left-right direction. In the absence of continuous prostate motion monitoring, and under ideal circumstances, 1-, 2-, and 3-mm vector planning margins require a respective imaging frequency of every 15, 60, and 240 to account for intrafraction prostate motion while achieving adequate geometric target coverage for 95% of the time.
在前列腺癌的少分次治疗中，分次内前列腺运动的校正变得非常重要。本研究的目的是在没有连续前列腺运动监测的情况下，估计一个理想的计划边缘，以作为成像和重新定位频率的函数来考虑分次内前列腺运动。
对 31 名接受调强放射治疗的患者进行了研究，在治疗过程中使用 Calypso 系统以 10 Hz 的频率对前列腺位置进行采样。利用这些数据，我们模拟了多种频率较低的成像方案，包括每 10、15、20、30、45、60、90、120、180 和 240 秒的间隔。对于每个成像方案，通过从该分次中的后续位移中减去前列腺位移来校正成像时间的前列腺位移。此外，我们进行了主成分分析以量化前列腺运动的方向。
对所有患者的每 240 和 60 秒的平均值进行直方图分析，前列腺的矢量位移在 95%的治疗时间内分别在 3 和 2mm 以内。对于 30 秒的成像，1mm 的矢量边缘可实现前列腺的 91.2%覆盖。对所有分次的主成分分析显示，前列腺位置在中矢状面的最大方差为 54°，从前方向开始，表明前上至后下是运动最大的方向。前列腺运动最小的方向是左右方向。
沿上下和前后方向的分次内前列腺运动幅度相当，运动最小的方向是左右方向。在没有连续前列腺运动监测的情况下，在理想情况下，1、2 和 3mm 的矢量计划边缘需要分别以每 15、60 和 240 秒的频率进行成像，以在 95%的时间内实现足够的几何靶区覆盖，从而考虑分次内前列腺运动。
