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Reconstruction Artifact Reduction in X-Ray Cone Beam CT Using a Treatment Couch Model

G Lasio

G Lasio1*, E Hu1 , J Zhou1 , M Lee1, B Yi1 , (1) University of Maryland School of Medicine, Baltimore, MD


SU-C-207-4 (Sunday, July 12, 2015) 1:00 PM - 1:55 PM Room: 207

Purpose: to mitigate artifacts induced by the presence of the RT treatment couch in on-board CBCT and improve image quality
Methods: a model of a Varian IGRT couch is constructed using a CBCT scan of the couch in air. The model is used to generate a set of forward projections (FP) of the treatment couch at specified gantry angles. The model couch forward projections are then used to process CBCT scan projections which contain the couch in addition to the scan object (Catphan phantom), in order to remove the attenuation component of the couch at any given gantry angle. Prior to pre-processing with the model FP, the Catphan projection data is normalized to an air scan with bowtie filter. The filtered Catphan projections are used to reconstruct the CBCT with an in-house FDK algorithm. The artifact reduction in the processed CBCT scan is assessed visually, and the image quality improvement is measured with the CNR over a few selected ROIs of the Catphan modules.
Results: Sufficient match between the forward projected data and the x-ray projections is achieved to allow filtering in attenuation space. Visual improvement of the couch induced artifacts is achieved, with a moderate expense of CNR.
Conclusion: Couch model-based correction of CBCT projection data has a potential for qualitative improvement of clinical CBCT scans, without requiring position specific correction data. The technique could be used to produce models of other artifact inducing devices, such as immobilization boards, and reduce their impact on patient CBCT images.

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