Quantification and correction of the scattered X-rays from a megavoltage photon beam to a linac-mounted kilovoltage imaging subsystem.
Quantification and correction of the scattered X-rays from a megavoltage photon beam to a linac-mounted kilovoltage imaging subsystem.
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DOI：
10.1259/bjro.20190048
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Mizowaki T
中科院分区：
文献类型：
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作者：
Iramina H;Nakamura M;Miyabe Y;Mukumoto N;Ono T;Hirashima H;Mizowaki T
量化和校正使用安装在直线上的千伏（kV）成像子系统获得的图像上的兆伏（MV）散射x射线（MV-scatter）。采用直线安装的平板探测器（FPD），仅在MV光束照射时激活FPD，即可获得包含MV散射的图像。使用6-，10-和15 MV带平坦滤波器（FF; 6X-FF, 10X-FF, 15X-FF），以及6-和10 MV不带FF （6X-FFF, 10X-FFF）。这些图是通过改变其中一个辐照参数而其他参数保持不变而获得的。将MV-scatter的平均像素值归一化为6X-FF参考条件（MV-scatter值）。利用这些值构建mv散射数据库。进行了一次全圆弧图像采集和两种方场尺寸（FSs）的mv散射校正实验。使用数据库进行基于测量和估计的校正。在每个角度下计算图像对比度。随着FS和剂量率的增大，mv散射增大。mv散射值因子根据FPD位置或准直器旋转而变化很大。在FS为10.0 × 10.0 cm2的情况下，未进行基于测量和基于估计的校正的图像对比度的中位相对误差范围分别为- 10.9至- 2.9、- 1.5至4.8和- 7.4至2.6。mv散射强烈依赖于FS、剂量率和FPD位置。mv散射校正提高了图像对比度。TrueBeam直线kV成像子系统上的MV散射与不同的MV光束参数有很大的关系，并且与场大小、剂量率和平板探测器位置密切相关。利用构建的数据库进行mv散射校正，提高了图像质量。
To quantify and correct megavoltage (MV) scattered X-rays (MV-scatter) on an image acquired using a linac-mounted kilovoltage (kV) imaging subsystem. A linac-mounted flat-panel detector (FPD) was used to acquire an image containing MV-scatter by activating the FPD only during MV beam irradiation. 6-, 10-, and 15 MV with a flattening-filter (FF; 6X-FF, 10X-FF, 15X-FF), and 6- and 10 MV without an FF (6X-FFF, 10X-FFF) were used. The maps were acquired by changing one of the irradiation parameters while the others remained fixed. The mean pixel values of the MV-scatter were normalized to the 6X-FF reference condition (MV-scatter value). An MV-scatter database was constructed using these values. An MV-scatter correction experiment with one full arc image acquisition and two square field sizes (FSs) was conducted. Measurement- and estimation-based corrections were performed using the database. The image contrast was calculated at each angle. The MV-scatter increased with a larger FS and dose rate. The MV-scatter value factor varied substantially depending on the FPD position or collimator rotation. The median relative error ranges of the contrast for the image without, and with the measurement- and estimation-based correction were −10.9 to −2.9, and −1.5 to 4.8 and −7.4 to 2.6, respectively, for an FS of 10.0 × 10.0 cm2. The MV-scatter was strongly dependent on the FS, dose rate, and FPD position. The MV-scatter correction improved the image contrast. The MV-scatters on the TrueBeam linac kV imaging subsystem were quantified with various MV beam parameters, and strongly depended on the fieldsize, dose rate, and flat panel detector position. The MV-scatter correction using the constructed database improved the image quality.