Tu and Yuen Center for Functional Onco-Imaging, Department of Radiological Sciences, University of California, Irvine, California, USA.
Int J Radiat Oncol Biol Phys. 2013 Oct 1;87(2):363-9. doi: 10.1016/j.ijrobp.2013.05.019. Epub 2013 Jul 9.
The objective of this work is to test the validity of the Gaussian approximation for prostate motion through characterization of its spatial distribution.
Real-time intrafraction prostate motion was observed using Calypso 4-dimensional (4D) nonradioactive electromagnetic tracking system. We report the results from a total of 1024 fractions from 31 prostate cancer patients. First, the correlation of prostate motion in right/left (RL), anteroposterior (AP), and superoinferior (SI) direction were determined using Pearson's correlation of coefficient. Then the spatial distribution of prostate motion was analyzed for individual fraction, individual patient including all fractions, and all patients including all fractions. The displacement in RL, AP, SI, oblique, or total direction is fitted into a Gaussian distribution, and a Lilliefors test was used to evaluate the validity of the hypothesis that the displacement is normally distributed.
There is high correlation in AP/SI direction (61% of fractions with medium or strong correlation). This is consistent with the longitudinal oblique motion of the prostate, and likely the effect from respiration on an organ confined within the genitourinary diaphragm with the rectum sitting posteriorly and bladder sitting superiorly. In all directions, the non-Gaussian distribution is more common for individual fraction, individual patient including all fractions, and all patients including all fractions. The spatial distribution of prostate motion shows an elongated shape in oblique direction, indicating a higher range of motion in the AP and SI directions.
Our results showed that the prostate motion is highly correlated in AP and SI direction, indicating an oblique motion preference. In addition, the spatial distribution of prostate motion is elongated in an oblique direction, indicating that the organ motion dosimetric modeling using Gaussian kernel may need to be modified to account for the particular organ motion character of prostate.
本研究旨在通过对前列腺运动的空间分布进行特征描述，检验前列腺运动的高斯近似的有效性。
采用 Calypso 四维（4D）非放射性电磁跟踪系统实时观察前列腺的分次内运动。我们报告了来自 31 例前列腺癌患者的总共 1024 个分次的结果。首先，使用 Pearson 相关系数确定了前列腺在右/左（RL）、前/后（AP）和上/下（SI）方向的运动相关性。然后，对单个分次、所有分次的单个患者和所有分次的所有患者的前列腺运动的空间分布进行了分析。RL、AP、SI、斜向或总方向的位移被拟合到高斯分布中，并使用 Lilliefors 检验评估了位移正态分布的假设的有效性。
AP/SI 方向的相关性很高（61%的分次具有中度或强相关性）。这与前列腺的纵向斜向运动一致，可能是由于呼吸作用导致位于生殖泌尿系统膈内的器官（直肠位于后方，膀胱位于上方）发生的运动。在所有方向上，单个分次、所有分次的单个患者和所有分次的所有患者中，非高斯分布更为常见。前列腺运动的空间分布在斜向方向上呈拉长形状，表明在 AP 和 SI 方向上的运动范围更大。
我们的结果表明，前列腺运动在 AP 和 SI 方向上具有高度相关性，表明存在斜向运动偏好。此外，前列腺运动的空间分布在斜向方向上呈拉长形状，表明在使用高斯核进行器官运动剂量学建模时，可能需要对前列腺的特定器官运动特征进行修正。
