Lindsay Josh W H, Meara Simon J P, Clarke Matthew, Lowe Matthew, Lines David, Aznar Marianne C, van Herk Marcel
Division of Cancer Sciences, The University of Manchester, Manchester, UK.
Department of Radiotherapy Related Research, The Christie NHS Foundation Trust, Manchester, UK.
Phys Imaging Radiat Oncol. 2025 Mar 13;34:100745. doi: 10.1016/j.phro.2025.100745. eCollection 2025 Apr.
BACKGROUND & PURPOSE: Cone-beam computed tomography (CBCT) images are used in image-guided radiotherapy to track anatomical changes throughout treatment and to set up patients to ensure accurate delivery of therapeutic radiation at each treatment session. An offline method of CBCT reconstruction workflow, operating on 2D projection images and specific to the imaging system in question, is needed for many image optimisation studies. Here we present a methodology to reconstruct CBCT images from these data for a commercial proton beam therapy machine, accounting for the variation in exposure and beam hardening from filtration due to gantry rotation during CBCT acquisition.
MATERIALS & METHODS: Projection data of solid water phantoms were acquired to model bow-tie filter motion and beam hardening effects. Projection data and system CBCT reconstructions of a Catphan504 phantom were acquired for validation of the method, as well as a retrospectively accessed patient image. The presented workflow was assessed against the clinical reconstructions using uniformity, signal-to-noise-ratio, and contrast-to-noise-ratio measured in the phantom images.
The offline workflow eliminated crescent artefacts due to variable exposure and beam hardening in phantom and patient images. Signal-to-noise and contrast-to-noise ratios were similar compared to system reconstructions, although with slight differences thought to be due to interplay effects in the bow-tie filter.
A workflow was developed to emulate the CBCT reconstruction process for a commercial proton therapy machine, providing a useful tool for optimised acquisition parameters and novel reconstruction processes using this system.
锥束计算机断层扫描（CBCT）图像用于图像引导放射治疗，以跟踪整个治疗过程中的解剖结构变化，并对患者进行摆位，以确保每次治疗时治疗性辐射的准确投照。许多图像优化研究需要一种离线的CBCT重建工作流程，该流程基于二维投影图像运行，且特定于所讨论的成像系统。在此，我们提出一种方法，用于从这些数据重建用于商用质子束治疗机的CBCT图像，同时考虑到在CBCT采集过程中由于机架旋转导致的滤过引起的曝光变化和束硬化。
采集固体水模体的投影数据，以模拟蝴蝶结滤过器运动和束硬化效应。采集Catphan504模体的投影数据和系统CBCT重建图像，用于方法验证，以及回顾性获取的患者图像。使用在模体图像中测量的均匀性、信噪比和对比噪声比，将所提出的工作流程与临床重建进行评估。
离线工作流程消除了由于模体和患者图像中曝光和束硬化变化导致的新月形伪影。与系统重建相比，信噪比和对比噪声比相似，尽管存在细微差异，认为这是由于蝴蝶结滤过器中的相互作用效应所致。
开发了一种工作流程，以模拟商用质子治疗机的CBCT重建过程，为使用该系统优化采集参数和新型重建过程提供了一种有用的工具。
