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Iterative reconstruction methods for treatment beam megavoltage computed tomography.

机译：迭代重建方法用于治疗束兆伏计算机断层扫描。

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The challenge posed by reconstructing image volumes with projections acquired at megavoltage photon energies presents an opportunity to investigate new methods of image reconstruction and image acquisition. These methods are developed with a goal of providing image-based approaches to important daily tasks encountered in radiotherapy including setup verification or post-treatment dosimetric verification. Constraints imposed by a need for dose efficiency, the availability of digital detection devices, and the standard method of image acquisition can lead to reconstructed volumes of poor quality which contain artifacts and possess little low-contrast detectability or spatial resolution. The work described in this dissertation focuses on overcoming constraints imposed by megavoltage computed tomography (MVCT) through the use of cone-beam algorithms from a well-known family of algebraic reconstruction methods and the use of novel image acquisition methods. Computer code is developed implementing two iterative algorithms—the algebraic reconstruction technique (ART) and the simultaneous algebraic reconstruction technique (SART). Using these software tools, the effects of different reconstruction parameters and image acquisition strategies are investigated using simulated image acquisitions of analytical phantoms as well as real-data acquisitions of physical phantoms. The case of limited-view reconstruction is given particular attention with respect to algorithm robustness and reconstruction quality. A method known as augmented MVCT is investigated for cone-beam ART-type implementations using a limited number of simulated treatment portal images combined with additional projection data. The tools and methods used during the simulation study are also used to investigate the feasibility of using projections, acquired with electronic portal imaging devices (EPIDs) attached to linear accelerators, along with MVCT to accomplish image-based radiotherapy verification. The results of this simulation study show the feasibility of limited-view cone-beam ART-type reconstruction and the applicability of these methods to EPID image acquisition and MVCT reconstruction in radiotherapy.
机译：用在兆伏光子能量下获得的投影来重建图像体积带来的挑战为研究图像重建和图像获取的新方法提供了机会。开发这些方法的目的是为放射治疗中遇到的重要日常任务提供基于图像的方法，包括设置验证或治疗后剂量学验证。对剂量效率的需求，数字检测设备的可用性以及图像采集的标准方法所施加的约束条件可能导致重建的质量差的体积，其中包含伪影并且几乎没有低对比度的可检测性或空间分辨率。本论文所描述的工作着重于通过使用著名的代数重构方法家族的锥束算法以及使用新颖的图像采集方法来克服兆伏计算机层析成像技术（MVCT）所施加的约束。通过执行两种迭代算法来开发计算机代码-代数重构技术（ART）和同时代数重构技术（SART）。使用这些软件工具，使用分析体模的模拟图像采集以及物理体模的真实数据采集，研究了不同重建参数和图像采集策略的影响。在算法稳健性和重建质量方面，特别关注有限视图重建的情况。使用有限数量的模拟治疗门图像与其他投影数据相结合的锥束ART型实施方式，研究了一种称为增强MVCT的方法。仿真研究中使用的工具和方法还用于调查使用投影仪的可行性，该投影仪是通过附接到线性加速器的电子门成像设备（EPID）以及MVCT来完成基于图像的放射治疗验证的。仿真研究的结果表明，有限视角锥束ART型重建的可行性以及这些方法在放射治疗中EPID图像获取和MVCT重建中的适用性。

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