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Impact of Gated and Conventional 4DCT Acquisition On Imaging Artifacts in a Digital Phantom

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K Bernatowicz

K Bernatowicz1*, P Keall2, J Kipritidis2, (1) Swiss Federal University of Technology, Zurich (2)The University of Sydney, Camperdown, NSW

SU-E-J-3 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: A new 4D computed tomography (4DCT) acquisition method based on displacement gating was simulated using a deformable digital cardiac-torso phantom. Imaging artifacts, delivered dose and acquisition time were compared with conventional image acquisition for lung radiation oncology.

Methods: Gated image acquisition was simulated with a computerized time resolved cardiac-torso (modified XCAT) phantom synchronized to patient tumor motion data. The gating threshold is based on the mean peak-to-peak displacement in the superior-inferior (SI) direction during free breathing. The conventional 4DCT was simulated to mimic typical clinical acquisition parameters, where the imager frequency and couch idle time are determined from the patient breathing trace and result in slight data oversampling. The quality of gated and conventional images was compared based on anatomical similarity with the known phantom geometry. Scan time and imaging dose were also compared, the latter of which is corresponds to the number of acquired images.

Results: The gated approach reduced the amount of imaging artifacts by up to 20% (including duplication, overlapping and incomplete structure) and allowed for better anatomical shape preservation. However, the total acquisition session time using gating increased by 17% compared to the conventional scan. With gating, shorter beam-on time reduced the dose delivered to the patient by 25% (200 fewer images were acquired with gating).

Conclusion:Gated 4DCT acquisition can improve image quality, which is beneficial for the highly conformal image guided radiation therapy planning. Furthermore, gated method lowers imaging dose on a cost of a longer imaging session. Further work will investigate different modes to compute gating tolerances to be tested on more challenging patient cases (e.g. including baseline shift).

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