Long-term Inter-protocol kV CBCT image quality assessment for a ring-gantry linac via automated QA approach

Jiayuan Peng, Hua Li, Eric Laugeman, Thomas Mazur, Dao Lam, Taoran Li, Baozhou Sun, Weigang Hu, Lei Dong, Geoffrey D. Hugo, Sasa Mutic, Bin Cai

Research output: Contribution to journalArticlepeer-review


We develop a fully automated QA process to compare the image quality of all kV CBCT protocols on a Halcyon linac with ring gantry design, and evaluate image quality stability over a 10-month period. A total of 19 imaging scan and reconstruction protocols were characterized with measurement on a newly released QUART phantom. A set of image analysis algorithms were developed and integrated into an automated analysis suite to derive key image quality metrics, including HU value accuracy on density inserts, HU uniformity using the background plate, high contrast resolution with the modulation transfer function (MTF) from the edge profiles, low contrast resolution using the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), slice thickness with the air gap modules, and geometric accuracy with the diameter of the phantom. Image quality data over 10 months was tracked and analyzed to evaluate the stability of the Halcyon kV imaging system. 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, range from 18.5-911.9 and 1.9-102.8, respectively. 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 slightly improved the MTF10% and MTF50% compared to the Feldkamp-Davis-Kress 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, which indicated the kV CBCT image quality is stable over time.

Original languageEnglish (US)
Article number015025
JournalBiomedical Physics and Engineering Express
Issue number1
StatePublished - 2020
Externally publishedYes


  • Halcyon kV CBCT
  • QUARTphantom
  • image quality
  • quality assurance

ASJC Scopus subject areas

  • Biophysics
  • Bioengineering
  • Biomaterials
  • Physiology
  • Biomedical Engineering
  • Radiology Nuclear Medicine and imaging
  • Computer Science Applications
  • Health Informatics


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