title: Optimal slice thickness for cone-beam CT with on-board imager.
abstract: OBJECTIVE
  To find the optimal slice thickness (Δτ) setting for patient registration with kilovoltage cone-beam CT (kVCBCT) on the Varian On Board Imager (OBI) system by investigating the relationship of slice thickness to automatic registration accuracy and contrast-to-noise ratio.
  
  
  METHODS
  Automatic registration was performed on kVCBCT studies of the head and pelvis of a RANDO anthropomorphic phantom. Images were reconstructed with 1.0 ≤ Δτ (mm) ≤ 5.0 at 1.0 mm increments. The phantoms were offset by a known amount, and the suggested shifts were compared to the known shifts by calculating the residual error. A uniform cylindrical phantom with cylindrical inserts of various known CT numbers was scanned with kVCBCT at 1.0 ≤ Δτ (mm) ≤ 5.0 at increments of 0.5 mm. The contrast-to-noise ratios for the inserts were measured at each Δτ.
  
  
  RESULTS
  For the planning CT slice thickness used in this study, there was no significant difference in residual error below a threshold equal to the planning CT slice thickness. For Δτ > 3.0 mm, residual error increased for both the head and pelvis phantom studies. The contrast-to-noise ratio is proportional to slice thickness until Δτ = 2.5 mm. Beyond this point, the contrast-to-noise ratio was not affected by Δτ.
  
  
  CONCLUSIONS
  Automatic registration accuracy is greatest when 1.0 ≤ Δτ (mm) ≤ 3.0 is used. Contrast-to-noise ratio is optimal for the 2.5 ≤ Δτ (mm) ≤ 5.0 range. Therefore 2.5 ≤ Δτ (mm) ≤ 3.0 is recommended for kVCBCT patient registration where the planning CT is 3.0 mm.
authors: London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada.
authors: Kyt
authors: K
authors: Seet
authors: A
authors: A
authors: Barghi
authors: S
authors: S
authors: Yartsev
authors: J
authors: J
authors: Van Dyk
references: Rofo. 2007 Jan;179(1):38-45
references: 17203442
references: Phys Med Biol. 2009 Oct 21;54(20):6251-62
references: 19794246
references: Phys Med Biol. 2007 Mar 21;52(6):1595-615
references: 17327651
references: Med Phys. 2008 Mar;35(3):1065-77
references: 18404941
references: Phys Med Biol. 2009 Dec 21;54(24):7263-83
references: 19926913
references: Med Phys. 2007 Oct;34(10):3732-8
references: 17985618
references: Med Phys. 2008 Mar;35(3):1145-53
references: 18404949
references: J Appl Clin Med Phys. 2006 Winter;7(1):97-104
references: 16518321
references: Phys Med Biol. 2007 Aug 7;52(15):N345-54
references: 17634636