On-board four-dimensional digital tomosynthesis: First experimental results

Abstract

The purpose of this study is to propose four-dimensional digital tomosynthesis (4D-DTS) for on-board analysis of motion information in three dimensions. Images of a dynamic motion phantom were reconstructed using acquisition scan angles ranging from 20 degrees (DTS) to full 360 degrees cone-beam computed tomography (CBCT). Projection images were acquired using an on-board imager mounted on a clinical linear accelerator. Three-dimensional (3D) images of the moving target were reconstructed for various scan angles. 3D respiratory correlated phase images were also reconstructed. For phase-based image reconstructions, the trajectory of a radiopaque marker was tracked in projection space and used to retrospectively assign respiratory phases to projections. The projections were then sorted according phase and used to reconstruct motion correlated images. By using two sets of projections centered about anterior-posterior and lateral axes, this study demonstrates how phase resolved coronal and sagittal DTS images can be used to obtain 3D motion information. Motion artifacts in 4D-DTS phase images are compared with those present in four-dimensional CT (4DCT) images. Due to the nature of data acquisition for the two modalities, superior-inferior motion artifacts are suppressed to a greater extent in 4D-DTS images compared with 4DCT. Theoretical derivations and experimental results are presented to demonstrate how optimal selection of image acquisition parameters including the frequency of projection acquisition and the phase window depend on the respiratory period. Two methods for acquiring projections are discussed. Preliminary results indicate that 4D-DTS can be used to acquire valuable kinetic information of internal anatomy just prior to radiation treatment.

Motion compensated digital tomosynthesis

“…An alternative to MC-DTS to mitigate respiratory motion induced artifacts is 4D DTS as described by Maurer et al [7], where subsets of projections are reconstructed in different phase bins. Consequently, the image quality of each phase is reduced due to the fact that a limited number of projections is reconstructed per bin.…”

“…Maurer et al [7] therefore developed four-dimensional DTS to mitigate such motion artifacts but hereby typically induce view aliasing artifacts due to coarse angular sampling.…”

Preliminary clinical evaluation of a 4D-CBCT estimation technique using prior information and limited-angle projections

“…Emerging hypo-fractionated treatment regimens such as lung stereotactic body radiation therapy [4–6] deliver a much higher radiation dose per fraction, which further necessitates accurate tumor localization. 4D on-board imaging techniques such as 4D cone-beam CT (CBCT) [7–10] and 4D digital tomosynthesis (DTS) [11–14] have found wider clinical interest recently to improve the localization accuracy of moving tumors. Compared with 3D imaging techniques, the 4D capacity of these techniques enables the trajectory of moving tumors to be captured, which can lead to better alignment of the target volume.…”

“…However, using the current clinical ‘gold-standard’ Feldkamp-Davis-Kress (FDK) [16] algorithm, 4D-CBCT reconstruction requires full-angle projection data, leading to an excessive amount of scanning time and imaging dose. In contrast, 4D-DTS reconstruction uses only limited-angle projection data, requiring less scanning time and imaging dose [11, 12]. However, 4D-DTS is limited by its degraded resolution along the plane-to-plane direction without full volumetric information, which may impair the tumor localization accuracy [17, 18].…”

Accuracy estimation for projection‐to‐volume targeting during rotational therapy: A feasibility study

“…12,13 More recently, the series of projections acquired during arc rotations has been used to estimate motion and deformation parameters. [14][15][16][17][18][19][20][21][22] This area of research is highly promising. As the amount of information needed to estimate the position, pose, configuration, and finally motion of a patient is reduced, the temporal resolution of updates to the patient state improves.…”