Data-driven rapid 4D Cone-Beam CT reconstruction for new generation linacs.


Newer generation linear accelerators (Linacs) allow 20 second cone-beam CT (CBCT) acquisition which reduces radiation therapy treatment time. However, the current clinical application of these rapid scans is only 3DCBCT. In this paper we propose a novel data-driven rapid 4DCBCT reconstruction method for new generation linacs.
Approach:
This method relies on estimating the magnitude of the diaphragm motion from an initial 3D reconstruction. This estimated motion is used to linearly approximate a deformation vector field (DVF) for each respiration phase. These DVFs are then used for motion compensated Feldkamp-Davis-Kress (MCFDK) reconstructions. This method, named MCFDK Data Driven (MCFDK-DD), was compared to a MCFDK reconstruction using a prior motion model (MCFDK-Prior), a 3D-FDK reconstruction, and a conventional acquisition (4 mins) conventional reconstruction 4DCBCT (4D-FDK). The data used in this paper were derived from 4DCT volumes from 13 patients from The Cancer Imaging Archives. The analysis metrics were the Mean Square Error (MSE), Structural Similarity Index Measurement (SSIM) and Tissue Interface Width (TIW).
Main Results:
The MCFDK-DD, MCFDK-Prior and 3D-FDK had median MSE values of 1.23×10-6mm-1, 1.14×10-6mm-1 and 1.19×10-6mm-1 respectively. The corresponding median SSIM values were 0.92, 0.92 and 0.92 respectively. These metrics indicated the MCFDK-DD had good agreement with the conventional 4D-FDK and were similar to the MCFDK-Prior reconstructions. The calculated TIW values from the MCFDK-DD reconstructions (median 18.7 mm) were not significantly different to the MCFDK-Prior (median 23.1 mm, p=0.087) and conventional 4D-FDK (median 21.4 mm, p=0.62) reconstruction methods. The TIW was also significantly reduced for the MCFDK-DD method compared to the 3D-FDK reconstructions (median 24.2 mm, p=0.01).
Significance:
These results demonstrate the feasibility of creating accurate data-driven 4DCBCT images for rapid scans on new generation linacs. These findings could lead to increased clinical usage of 4D information on newer generation linacs.&#xD.