Quantification of shape variation of prostate and seminal vesicles during external beam radiotherapy
Quantification of shape variation of prostate and seminal vesicles during external beam radiotherapy
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DOI：
10.1016/j.ijrobp.2004.09.023
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发表时间：
2005-01-01
影响因子：
7
通讯作者：
van Herk, M
中科院分区：
文献类型：
--
作者：
Deurloo, KEI;Steenbakkers, RJHM;van Herk, M
目的：已知前列腺在直肠充盈变化的影响下平移和旋转，并且许多研究已经解决了这些运动的幅度。然而，前列腺形状的变化也有报道。对于图像引导的放射治疗，必须知道平移、旋转和形状变化的相对大小，以便可以选择最合适的校正策略。然而，尚未对形状变化进行定量分析。因此，本文的目的是开发一种方法，以确定复杂的器官的形状变化，并将其应用于确定形状变化的GTV（总肿瘤体积）组成的前列腺和精囊。方法和材料：对于这项研究，19例前列腺癌患者的数据。每例患者接受计划计算机断层扫描（CT）扫描和8-12（平均11）重复CT扫描，在适形放疗过程中。一名观察者在所有扫描中描绘了GTV，并测量了体积变化。在匹配每个患者的平移和旋转的GTV后，构建覆盖概率矩阵，并采用50%等值面来确定平均GTV表面。计算平均GTV的每个点的平均GTV和个体GTV之间的周向距离，并以局部标准差（SD）表示其变化。所有19名患者的形状变化的局部SD通过匹配和变形的个人平均GTV映射到参考情况。对6例患者重复描绘GTV，以确定观察者内变异。最后，测量的形状变化进行校正观察者内的变化，以估计“真实的”形状variation.Results：没有显着的变化，GTV体积观察。测量的形状变化（包括轮廓变化）在囊泡尖端最大（SD = 2.0 mm），在前列腺左侧和右侧最小（SD = 1.0 mm），其他地方平均（SD = 1.5 mm）。在前列腺的左侧、右侧和颅侧，观察者内变化与测量的形状变化具有相同的数量级;其他地方较小。然而，观察者内变化的估计SD的准确度约为测量形状变化的估计SD准确度的一半，在“真实的”形状变化的估计中给出了最大0.6 mm SD的总体不确定性。在前列腺的左、右和头侧，“真实的”形状变化较小（SD
Purpose: The prostate is known to translate and rotate under influence of rectal filling changes and many studies have addressed the magnitude of these motions. However, prostate shape variations also have been reported. For image-guided radiotherapy, it is essential to know the relative magnitude of translations, rotations, and shape variation so that the most appropriate correction strategy can be chosen. However, no quantitative analysis of shape variation has been performed. It is, therefore, the purpose of this article to develop a method to determine shape variation of complex organs and apply it to determine shape variation during external beam radiotherapy of a GTV (gross tumor volume) consisting of prostate and seminal vesicles.Methods and Materials: For this study, the data of 19 patients with prostate cancer were used. Each patient received a planning computed tomography (CT) scan and 8-12 (11 on average) repeat CT scans that were made during the course of conformal radiotherapy. One observer delineated the GTV in all scans, and volume variations were measured. After matching the GTVs for each patient for translation and rotation, a coverage probability matrix was constructed and the 50% isosurface was taken to determine the average GTV surface. Perpendicular distances between the average GTV and the individual GTVs were calculated for each point of the average GTV, and their variation was expressed in terms of local standard deviation (SD). The local SDs of the shape variation of all 19 patients were mapped onto a reference case by matching and morphing of the individual average GTVs. Repeated delineation of the GTV was done for 6 patients to determine intraobserver variation. Finally, the measured shape variation was corrected for intraobserver variation to estimate the "real" shape variation.Results: No significant variations in GTV volume were observed. The measured shape variation (including delineation variation) was largest at the tip of the vesicles (SD = 2.0 mm), smallest at the left and right side of the prostate (SD = 1.0 mm), and average elsewhere (SD = 1.5 mm). At the left, right, and cranial sides of the prostate, the intraobserver variation was of the same order of magnitude as the measured shape variation; elsewhere it was smaller. However, the accuracy of the estimated SD for intraobserver variation was about half of the accuracy of the estimated SD for the measured shape variation, giving an overall uncertainty of maximum 0.6 mm SD in the estimate of the "real" shape variation. The "real" shape variation was small at the left, right, and cranial side of the prostate (SD