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JACK KROHMER JUNIOR INVESTIGATOR COMPETITION WINNER: Development and Evaluation of a Two Dimensional Antiscatter Grid for CBCT


T Alexeev

T Alexeev*, B Kavanagh , M Miften , C Altunbas , University of Colorado School of Medicine, Aurora, CO

Presentations

WE-F-605-1 (Wednesday, August 2, 2017) 1:45 PM - 3:45 PM Room: 605


Purpose: A novel 2D antiscatter grid (ASG) was designed and fabricated to reduce the scatter induced image quality degradation in CBCT. In this work, we integrated the 2DASG prototype with a linac mounted CBCT system, and evaluated the improvement in CBCT image quality.

Methods: A 2DASG prototype with septal thickness of 0.1 mm, and grid ratio of 8.2 was fabricated by using powder bed laser melting additive manufacturing process. 2DASG was mounted directly on the flat panel detector in Varian TrueBeam CBCT system. A gantry angle specific flat-field correction method was implemented to remove grid artifacts induced by gantry sag during CBCT acquisitions. CBCT images were reconstructed using a modified FDK algorithm. CT number accuracy and contrast to noise ratio (CNR) were assessed using different sized phantoms to modulate the primary and scatter intensity. Two configurations were evaluated under identical imaging conditions: Without ASG and with 2D ASG.

Results: To assess the Hounsfield Unit (HU) accuracy, mean HU was measured in eight regions of interest (ROIs) in a large uniform density phantom. Without 2DASG, the average HU across ROIs were underestimated by 300±79 HU. With 2DASG, HU underestimation was reduced down to 43±15 HU in the largest phantom evaluated in this study. Without 2DASG, CNR in polystyrene, LDPE and Teflon inserts were 1.1, 1.3, and 10 respectively. With 2DASG, CNR was increased to 3.2, 3.3, and 18 at the same material insert locations, respectively.

Conclusion: 2DASG prototype provided significant improvements in both CT number accuracy and low contrast resolution. We strongly believe that an optimized 2D ASG design can potentially enable utilization of CBCT imaging in applications that require high CT number accuracy, such as CBCT based treatment planning in radiation therapy. Additionally, improved contrast resolution provided by 2DASG may also translate into better soft tissue visualization in CBCT imaging.

Funding Support, Disclosures, and Conflict of Interest: This research project was supported in part by NIH/NCI under Award Number R21CA198462. The GPU unit employed in this work was donated by NVIDIA corporation.


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