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评估不同千伏成像模式在部分乳腺照射设置中的夹子定位情况。

Evaluation of clip localization for different kilovoltage imaging modalities as applied to partial breast irradiation setup.

作者信息

Buehler Andreas, Ng Sook-Kien, Lyatskaya Yulia, Stsepankou Dzmitry, Hesser Jurgen, Zygmanski Piotr

机构信息

University Medical Centre Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, D-68167 Mannheim, Germany.

出版信息

Med Phys. 2009 Mar;36(3):821-34. doi: 10.1118/1.3075904.

Abstract

Surgical clip localization and image quality were evaluated for different types of kilovoltage cone beam imaging modalities as applied to partial breast irradiation (PBI) setup. These modalities included (i) clinically available radiographs and cone beam CT (CB-CT) and (ii) various alternative modalities based on partial/sparse/truncated CB-CT. An anthropomorphic torso-breast phantom with surgical clips was used for the imaging studies. The torso phantom had artificial lungs, and the attached breast phantom was a mammographic phantom with realistic shape and tissue inhomogeneities. Three types of clips of variable size were used in two orthogonal orientations to assess their in-/cross-plane characteristics for image-guided setup of the torso-breast phantom in supine position. All studies were performed with the Varian on-board imaging (OBI, Varian) system. CT reconstructions were calculated with the standard Feldkamp-Davis-Kress algorithm. First, the radiographs were studied for a wide range of viewing angles to characterize image quality for various types of body anatomy in the foreground/background of the clips. Next, image reconstruction quality was evaluated for partial/sparse/truncated CB-CT. Since these modalities led to reconstructions with strong artifacts due to insufficient input data, a knowledge-based CT reconstruction method was also tested. In this method, the input data to the reconstruction algorithm were modified by combining complementary data sets selected from the treatment and reference projections. Different partial/sparse/truncated CB-CT scan types were studied depending on the total are angle, angular increment between the consequent views (CT projections), orientation of the arc center with respect to the imaged breast and chest wall, and imaging field size. The central angles of the viewing arcs were either tangential or orthogonal to the chest wall. Several offset positions of the phantom with respect to the reference position were studied. The acquired and reconstructed image data sets were analyzed using home-built software focusing on the ability to localize clips in 3D. Streaking and leakage reconstruction artifacts and spatial distortions of breast surface were analyzed as well. Advantages and disadvantages of each kilovoltage CB imaging modality as applied to partial breast setup evaluation based on clips are presented. Because clips were found to be difficult to recognize in radiographs, 3D reconstructions were preferred. Even though it was possible to localize clips with about +/-1 mm accuracy based on reconstructions for short arcs of 40 degrees and incremental angle up to about 5 degrees, identification of clips in such reconstructions is difficult. Reconstructions obtained for arcs of as low as 80 degrees and incremental angle of as high as 3 degrees were suggested for easier clip identification. For more severely undersampled data, iterative CB-CT reconstruction is recommended to decrease the artifacts.

摘要

针对应用于部分乳腺照射(PBI)设置的不同类型千伏级锥束成像模式,评估了手术夹定位和图像质量。这些模式包括:(i)临床可用的X线片和锥束CT(CB-CT),以及(ii)基于部分/稀疏/截断CB-CT的各种替代模式。使用带有手术夹的拟人化躯干-乳房体模进行成像研究。躯干体模有仿真肺,附着的乳房体模是具有逼真形状和组织不均匀性的乳腺摄影体模。使用三种不同尺寸的夹子,以两个正交方向放置,以评估其在仰卧位的躯干-乳房体模图像引导设置中的平面内/平面交叉特征。所有研究均使用瓦里安机载成像(OBI,瓦里安)系统进行。采用标准的费尔德坎普-戴维斯-克雷斯算法进行CT重建。首先,研究了X线片在广泛视角下的情况,以表征夹子前景/背景中各种类型身体解剖结构的图像质量。接下来,评估了部分/稀疏/截断CB-CT的图像重建质量。由于这些模式因输入数据不足导致重建出现严重伪影,还测试了一种基于知识的CT重建方法。在该方法中,通过组合从治疗和参考投影中选择的互补数据集来修改重建算法的输入数据。根据总弧角、连续视图(CT投影)之间的角度增量、弧中心相对于成像乳房和胸壁的方向以及成像视野大小,研究了不同的部分/稀疏/截断CB-CT扫描类型。观察弧的中心角与胸壁相切或正交。研究了体模相对于参考位置的几个偏移位置。使用自制软件分析采集和重建的图像数据集,重点关注在三维空间中定位夹子的能力。还分析了条纹和泄漏重建伪影以及乳房表面的空间变形。介绍了每种千伏级CB成像模式应用于基于夹子的部分乳腺设置评估的优缺点。由于发现夹子在X线片中难以识别,因此首选三维重建。尽管基于40度短弧和高达约5度的增量角的重建可以以约±1毫米的精度定位夹子,但在这种重建中识别夹子很困难。建议采用低至80度的弧和高达3度的增量角进行重建,以便更轻松地识别夹子。对于欠采样更严重的数据,建议采用迭代CB-CT重建以减少伪影。

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