title: Evaluation of gantry speed on image quality and imaging dose for 4D cone-beam CT acquisition.
abstract: BACKGROUND
  This study investigates the effect of gantry speed on 4DCBCT image quality and dose for the Varian On-Board Imager®.
  
  
  METHODS
  A thoracic 4DCBCT protocol was designed using a 125 kVp spectrum. Image quality parameters were evaluated for 4DCBCT acquisition using Catphan® phantom with real-time position management™ system for gantry speeds varying between 1.0 to 6.0°/s. Superior-inferior motion of the phantom was executed using a sinusoidal waveform with five second period. Scans were retrospectively sorted into 4 phases (CBCT-4 ph) and 10 phases (CBCT-10 ph); average 4DCBCT (CBCT-ave), using all image data from the 4DCBCT acquisitions was also evaluated. The 4DCBCT images were evaluated using the following image quality metrics: spatial resolution, contrast-to-noise ratio (CNR), and uniformity index (UI). Additionally, Hounsfield unit (HU) sensitivity compared to a baseline CBCT and percent differences and RMS errors (RMSE) of excursion were also determined. Imaging dose was evaluated using an IBA CC13 ion chamber placed within CIRS Thorax phantom using the same sinusoidal motion and image acquisition settings as mentioned above.
  
  
  RESULTS
  Spatial resolution decreased linearly from 5.93 to 3.82 lp/cm as gantry speed increased from 1.0 to 6.0°/s. CNR decreased linearly from 4.80 to 1.82 with gantry speed increasing from 1.0 to 6.0°/s, respectively. No noteworthy variations in UI, HU sensitivity, or excursion metrics were observed with changes in gantry speed. Ion chamber dose rates measured ranged from 2.30 (lung) to 5.18 (bone) E-3 cGy/mAs.
  
  
  CONCLUSIONS
  A quantitative analysis of the Varian OBI's 4DCBCT capabilities was explored. Changing gantry speed changes the number of projections used for reconstruction, affecting both image quality and imaging dose if x-ray tube current is held constant. From the results of this study, a gantry speed between 2 and 3°/s was optimal when considering image quality, dose, and reconstruction time. The future of 4DCBCT clinical utility relies on further investigation of image acquisition and reconstruction optimization.
authors.affiliation: Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, MI, 48201, USA.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Santoso
authors.affiliation: Texas Oncology, Fort Worth, TX, 76104, USA.|Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, 48202, USA.
authors.forename: Kwang H
authors.initials: KH
authors.lastname: Song
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, 48202, USA.
authors.forename: Yujiao
authors.initials: Y
authors.lastname: Qin
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, 48202, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Gardner
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, 48202, USA.
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, 48202, USA.
authors.forename: Indrin J
authors.initials: IJ
authors.lastname: Chetty
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, 48202, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Movsas
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, 48202, USA.
authors.forename: Munther
authors.initials: M
authors.lastname: Ajlouni
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, 48202, USA. nwen1@hfhs.org.
authors.forename: Ning
authors.initials: N
authors.lastname: Wen
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012119:Respiration; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*
keywords: Cone-beam CT; Dosimetry; Image guidance; Motion management