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Long-Term Inter-Protocol KV CBCT Image Quality Assessment On the Halcyon Linac Via An Automated QA Approach with the QUART Phantom

J Peng1,2,3, H Li3 , E Laugeman3 , T Mazur3 , D Lam3 , T Li4 , B Sun3 , W Hu1,2 , L Dong4 , G Hugo3 , S Mutic3 , B Cai3* , (1) Department of Radiation Oncology, Fundan University Shanghai Cancer Center, Shanghai, China, (2) Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China, (3) Department of Radiation Oncology, Washington University, St. Louis, MO, USA, (4) Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To develop a fully automated QA process to compare the image quality of all kV CBCT protocols and evaluate their long-term stability on a Halcyon 2.0 platform with the ring gantry design.

Methods: A set of image analysis algorithms were developed to derive key image quality metrics, including HU value accuracy on the density inserts, HU uniformity check using the background plate, high contrast resolution evaluation with the modulation transfer function (MTF) from the edge profiles, low contrast resolution analysis using the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), slice thickness calculation with the air gap modules, and geometric accuracy with the diameter of the phantom. Long-term image quality data over 10 months was tracked and analyzed to evaluate the stability of the Halcyon kV imaging system.

Results: The HU accuracy over all 19 protocols is within tolerance (±50HU). The maximum uniformity deviation is 12.2 HU. The SNR and CNR, depending on the protocol selected, ranges from 18.5-911.9 and 1.9-102.8. A much improved SNR and CNR were observed for iterative reconstruction (iCBCT) modes and protocols designed for large subjects over low dose and fast scanning modes. The Head and Image Gently protocols have the greatest high contrast resolution with MTF10% over 1 lp/mm and MTF50% over 0.6 lp/mm. The iCBCT mode improved the MTF10% and MTF50% compared to the regular FDK approach. The slice thickness (maximum error of 0.31 mm) and geometry metrics (maximum error of 0.7 mm) are all within tolerance (±0.5 mm for slice thickness and ±1 mm for geometry metrics).The long-term study over 10-month showed no significant drift for all key image quality metrics.

Conclusion: The inter-protocol image analysis shows all protocols on the second generation Halcyon system are suitable for clinical use. The long term reproducibility shows the kV CBCT image quality is quite stable.

Funding Support, Disclosures, and Conflict of Interest: This project received funding from Varian Medical System.


Not Applicable / None Entered.


IM- Cone Beam CT: Development (New Technology and Techniques)

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