Wu Guorong, Wang Qian, Lian Jun, Shen Dinggang
Department of Radiology and BRIC, University of North Carolina at Chapel Hill, USA.
Inf Process Med Imaging. 2011;22:686-98. doi: 10.1007/978-3-642-22092-0_56.
In the radiation therapy of lung cancer, a free-breathing 3D-CT image is usually acquired in the treatment day for image-guided patient setup, by registering with the free-breathing 3D-CT image acquired in the planning day. In this way, the optimal dose plan computed in the planning day can be transferred onto the treatment day for cancer radiotherapy. However, patient setup based on the simple registration of the free-breathing 3D-CT images of the planning and the treatment days may mislead the radiotherapy, since the free-breathing 3D-CT is actually the mixed-phase image, with different slices often acquired from different respiratory phases. Moreover, a 4D-CT that is generally acquired in the planning day for improvement of dose planning is often ignored for guiding patient setup in the treatment day. To overcome these limitations, we present a novel two-step method to reconstruct the 4D-CT from a single free-breathing 3D-CT of the treatment day, by utilizing the 4D-CT model built in the planning day. Specifically, in the first step, we proposed a new spatial-temporal registration algorithm to align all phase images of the 4D-CT acquired in the planning day, for building a 4D-CT model with temporal correspondences established among all respiratory phases. In the second step, we first determine the optimal phase for each slice of the free-breathing (mixed-phase) 3D-CT of the treatment day by comparing with the 4D-CT of the planning day and thus obtain a sequence of partial 3D-CT images for the treatment day, each with only the incomplete image information in certain slices; and then we reconstruct a complete 4D-CT for the treatment day by warping the 4D-CT of the planning day (with complete information) to the sequence of partial 3D-CT images of the treatment day, under the guidance of the 4D-CT model built in the planning day. We have comprehensively evaluated our 4D-CT model building algorithm on a public lung image database, achieving the best registration accuracy over all other state-of-the-art methods. Also, we have validated our proposed 4D-CT reconstruction algorithm on the simulated free-breathing data, obtaining very promising 4D-CT reconstruction results.
在肺癌放射治疗中，通常在治疗当天获取自由呼吸的三维计算机断层扫描（3D-CT）图像用于图像引导的患者摆位，通过将其与计划当天获取的自由呼吸3D-CT图像进行配准。通过这种方式，在计划当天计算出的最佳剂量计划可以转移到治疗当天用于癌症放射治疗。然而，基于计划和治疗当天自由呼吸3D-CT图像的简单配准进行患者摆位可能会误导放射治疗，因为自由呼吸3D-CT实际上是混合相位图像，不同的切片通常是在不同的呼吸相位获取的。此外，通常在计划当天获取的用于改进剂量计划的四维计算机断层扫描（4D-CT）在治疗当天用于引导患者摆位时常常被忽视。为了克服这些限制，我们提出了一种新颖的两步法，通过利用计划当天建立的4D-CT模型，从治疗当天的单个自由呼吸3D-CT重建4D-CT。具体而言，第一步，我们提出了一种新的时空配准算法，用于对齐计划当天获取的4D-CT的所有相位图像，以建立一个在所有呼吸相位之间建立了时间对应关系的4D-CT模型。第二步，我们首先通过与计划当天的4D-CT进行比较，确定治疗当天自由呼吸（混合相位）3D-CT的每个切片的最佳相位，从而获得治疗当天的一系列部分3D-CT图像，每个图像在某些切片中仅具有不完整的图像信息；然后，在计划当天建立的4D-CT模型的指导下，通过将计划当天的4D-CT（具有完整信息）扭曲到治疗当天的部分3D-CT图像序列，重建治疗当天的完整4D-CT。我们在一个公共肺部图像数据库上全面评估了我们的4D-CT模型构建算法，在所有其他现有最先进方法中实现了最佳的配准精度。此外，我们在模拟的自由呼吸数据上验证了我们提出的4D-CT重建算法，获得了非常有前景的4D-CT重建结果。
