A piecewise-focused high DQE detector for MV imaging
A piecewise-focused high DQE detector for MV imaging
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DOI：
10.1118/1.4927786
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发表时间：
2015-09-01
期刊：
影响因子：
3.8
通讯作者：
Fahrig, Rebecca
中科院分区：
文献类型：
--
作者：
Star-Lack, Josh;Shedlock, Daniel;Fahrig, Rebecca
目的：寻找具有高探测量子效率(DQE)的电子射野成像器(EPID)，以便于将兆伏(MV)放射治疗射束用于图像引导。潜在的优势包括高质量(治疗)射束的眼部成像，以及改进的锥束计算机断层扫描(CBCT)，生成的图像具有更准确的电子密度图，不受金属伪影的影响。提高探测器灵敏度的一种方法是将厚的像素化闪烁体阵列耦合到结合了非晶硅薄膜电子器件的有源矩阵平板成像器(AMFPI)。钨酸镉(CWO)具有许多理想的闪烁性能，包括良好的光输出、高折射率、高光学透明度和合理的成本。然而，由于其晶体结构中固有的解理面，切割和抛光CWO的难度在一定程度上限制了它相对于其他闪烁体如碘化铯和锗酸铋(BGO)的研究。本工作的目标是建立和测试一个聚焦的大面积像素化的CWO探测器。方法：构建一个361×52 mm的闪烁体组件，总像素为28 072。该组件由七个子阵列组成，每个子阵列厚15 mm。其中六个子阵列是由CWO制成的，像素间距为0.784 mm，而一个阵列是由BGO构建的用于比较。聚焦是通过分段线性弧形光纤板将阵列耦合到VARIAN AS1000 AMFPI来实现的。利用6 MV束流进行了调制传递函数(MTF)和DQE的模拟和实验研究，并将像素化条带组件的性能与最常见的EPID配置进行了比较，EPID配置包括1 mm厚的铜堆积板，连接到133 mg/cm(2)GdO_2闪烁体屏幕(Cu-GOS)。采集体模的投影片和CBCT图像。该工作还介绍了使用轻量级边缘体模来产生mV能量下的MTF测量，并展示了其与更繁琐的基于狭缝的方法的功能等价性。结果：像素化连续波探测器的DQE(0)S的实测值和模拟值分别为22%和26%。在0.0-0.62 mm(-1)的频率范围内，CWO DQE(F)与CuGOS DQE(F)的实测值和模拟值的平均值分别为23和29。2D和3D成像研究证实了大剂量效率的改善，并且焦点在整个视野中保持不变。CWO CBCT图像的空间分辨率为7lp/cm。对比度-噪声比显着提高，反映了相对于铜-GOS的22倍灵敏度提高。CWO闪烁体材料表现出比BGO材料更高的稳定性和光产额。结论：描述了一种用于MV成像的高效分段聚焦像素化条形闪烁体，其剂量效率比Cu-GOS提高了20多倍。(C)2015年美国医学物理学家协会。
Purpose: Electronic portal imagers (EPIDs) with high detective quantum efficiencies (DQEs) are sought to facilitate the use of the megavoltage (MV) radiotherapy treatment beam for image guidance. Potential advantages include high quality (treatment) beam's eye view imaging, and improved cone-beam computed tomography (CBCT) generating images with more accurate electron density maps with immunity to metal artifacts. One approach to increasing detector sensitivity is to couple a thick pixelated scintillator array to an active matrix flat panel imager (AMFPI) incorporating amorphous silicon thin film electronics. Cadmium tungstate (CWO) has many desirable scintillation properties including good light output, a high index of refraction, high optical transparency, and reasonable cost. However, due to the < 0 1 0 > cleave plane inherent in its crystalline structure, the difficulty of cutting and polishing CWO has, in part, limited its study relative to other scintillators such as cesium iodide and bismuth germanate (BGO). The goal of this work was to build and test a focused large-area pixelated "strip" CWO detector.Methods: A 361 x 52 mm scintillator assembly that contained a total of 28 072 pixels was constructed. The assembly comprised seven subarrays, each 15 mm thick. Six of the subarrays were fabricated from CWO with a pixel pitch of 0.784 mm, while one array was constructed from BGO for comparison. Focusing was achieved by coupling the arrays to the Varian AS1000 AMFPI through a piecewise linear arc-shaped fiber optic plate. Simulation and experimental studies of modulation transfer function (MTF) and DQE were undertaken using a 6 MV beam, and comparisons were made between the performance of the pixelated strip assembly and the most common EPID configuration comprising a 1 mm-thick copper build-up plate attached to a 133 mg/cm(2) gadolinium oxysulfide scintillator screen (Cu-GOS). Projection radiographs and CBCT images of phantoms were acquired. The work also introduces the use of a lightweight edge phantom to generate MTF measurements at MV energies and shows its functional equivalence to the more cumbersome slit-based method.Results: Measured and simulated DQE(0)'s of the pixelated CWO detector were 22% and 26%, respectively. The average measured and simulated ratios of CWO DQE(f) to Cu-GOS DQE(f) across the frequency range of 0.0-0.62 mm(-1) were 23 and 29, respectively. 2D and 3D imaging studies confirmed the large dose efficiency improvement and that focus was maintained across the field of view. In the CWO CBCT images, the measured spatial resolution was 7 lp/cm. The contrast-to-noise ratio was dramatically improved reflecting a 22x sensitivity increase relative to Cu-GOS. The CWO scintillator material showed significantly higher stability and light yield than the BGO material.Conclusions: An efficient piecewise-focused pixelated strip scintillator for MV imaging is described that offers more than a 20-fold dose efficiency improvement over Cu-GOS. (C) 2015 American Association of Physicists in Medicine.