title: Technical note: a method for improving the calibration reproducibility of an ionization chamber detector array.
abstract: OBJECTIVE
  This paper describes an extension to a wide field calibration method implemented on a commercial detector array in order to improve the reproducibility of the calibration procedure.
  
  
  METHODS
  Following the standard array calibration procedure, two additional 10×10 cm exposures were acquired for each array axis with the detector array shifted by ±10 cm in the transverse or axial axes, or by ±10√2 cm in the positive or negative diagonal axes. These exposures were compared with a final baseline 10×10 cm exposure captured with the detector repositioned at the isocenter. The measurements were used to calculate a linear off-axis correction gradient which was then applied to the stored calibration factors.
  
  
  RESULTS
  The mean coefficient of variation between five repeat calibrations was reduced from 4.17% to 0.48% and the maximum percentage error in individual calibration factors was reduced from 6.46% to 0.77%.
  
  
  CONCLUSIONS
  The reproducibility of the calibration factors of an ionization chamber array was increased by capturing a baseline exposure and two further off-axis readings per calibration axis.
authors.affiliation: Brighton and Sussex University Hospitals NHS Trust, Eastern Road, Brighton BN2 5BE, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Goodall
authors.affiliation: Brighton and Sussex University Hospitals NHS Trust, Eastern Road, Brighton BN2 5BE, United Kingdom.
authors.forename: Steve
authors.initials: S
authors.lastname: Morgan
mesh_terms: D002138:Calibration; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D015203:Reproducibility of Results; D014867:Water
chemical_list: D014867:Water