Markerless Four-Dimensional-Cone Beam Computed Tomography Projection-Phase Sorting Using Prior Knowledge and Patient...

Area of Science:

• Medical Imaging
• Radiotherapy Physics
• Computational Anatomy

Background:

• Four-dimensional-cone beam computed tomography (4D-CBCT) is crucial for radiotherapy tumor targeting, requiring accurate sorting of projections into respiratory phases.
• Current phase sorting methods using external surrogates or 2D internal structures have limitations in accuracy and applicability.
• Markerless and robust phase sorting is needed for reliable 4D-CBCT reconstruction.

Purpose of the Study:

• To investigate the feasibility of a 3D motion modeling approach for markerless projection-phase sorting in 4D-CBCT.
• To develop and validate a method utilizing principal component analysis (PCA) for respiratory motion characterization.
• To assess the accuracy of the proposed method in digital phantoms and patient data.

Main Methods:

• Utilized patient 4D-CT images as prior information for 3D motion modeling.
• Applied Principal Component Analysis (PCA) to extract dominant respiratory deformation patterns.
• Solved PCA coefficients for each projection by matching with digitally reconstructed radiographs (DRRs) of deformed prior CTs.
• Employed PCA coefficients for projection-phase sorting.

Main Results:

• PCA-based sorting accurately reflected breathing motion patterns in anteroposterior and superoinferior directions in digital phantoms (XCATs).
• Achieved mean phase sorting differences below 2% with 100% of projections within 10% phase difference in XCATs.
• Patient data demonstrated mean phase differences from 1.62% to 2.23%, with 98.4%-100% of projections within 10% phase difference.

Conclusions:

• The study successfully demonstrated the feasibility of using PCA coefficients for accurate 4D-CBCT projection-phase sorting.
• The 3D motion modeling method provides a robust and automatic solution for 4D-CBCT reconstruction.
• This markerless approach enhances tumor target verification accuracy in radiotherapy without external surrogates or internal markers.