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Non-Planar CBCT Imaging for Gamma Knife Icon

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E Pearson

E Pearson1*, H Nordstrom2 , M Eriksson2 , D Jaffray1, (1) University Health Network, Toronto, ON, (2) Elekta Instrument, AB, Stockholm,


TU-H-605-5 (Tuesday, August 1, 2017) 4:30 PM - 6:00 PM Room: 605

Purpose: The Leksell Gamma Knife is a platform for precision cranial radiosurgery. The Icon model includes on-board cone-beam CT (CBCT) imaging capabilities. Since the X-ray beam cannot penetrate the frame fixation, a half cone geometry is used which aligns the x-ray field parallel and near the upper plane of the frame. The half-cone geometry maximizes the field-of-view attainable with these constraints but the large cone-angle can result in more pronounced cone-beam artifacts. Utilizing a non-planar imaging trajectory which incorporates a translation prior to the standard arc increases the sampling through the superior extent of the image volume and can reduce cone-angle artifacts.

Methods: A set of task-specific geometric phantoms and a standard anthropomorphic phantom were used to simulate projection data with the system geometry. The data are reconstructed with FDK for the standard arc and with ART for the trajectories with and without the line segment. The geometric phantom designs provide quantitative measures of CT# accuracy, contrast, resolution and noise metrics at a range of positions throughout the imaging volume. The anthropomorphic phantom allows for visual inspection of artifacts for relevant anatomic structures. Additionally, real data of a geometric phantom was acquired and the reconstructions shown.

Results: The reconstructions, FDK and ART, for this half-cone geometry from a standard rotation present with common cone-angle artifacts clearly in both visual inspection and in the quantitative measures of resolution and CT number accuracy which degrade away from the source plane. The additional projection data along the line segment substantially improves the consistency of the image quality over the axial field of view as demonstrated with both simulation and real data.

Conclusion: The incorporation of additional projection data off the plane of rotation can help overcome common artifacts for large cone-angle CBCT reconstructions such as the half-cone geometry in the Gamma Knife Icon.

Funding Support, Disclosures, and Conflict of Interest: This work was funded in part by Elekta Instrument, AB, Stockholm, Sweden.

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