title: Technical Note: Measurement of bow tie profiles in CT scanners using radiochromic film.
abstract: OBJECTIVE
  To provide a noninvasive technique to measure the intensity profile of the fan beam in a computed tomography (CT) scanner that is cost effective and easily implemented without the need to access proprietary scanner information or service modes.
  
  
  METHODS
  The fabrication of an inexpensive aperture is described, which is used to expose radiochromic film in a rotating CT gantry. A series of exposures is made, each of which is digitized on a personal computer document scanner, and the resulting data set is analyzed to produce a self-consistent calibration of relative radiation exposure. The bow tie profiles were analyzed to determine the precision of the process and were compared to two other measurement techniques, direct measurements from CT gantry detectors and a dynamic dosimeter.
  
  
  RESULTS
  The radiochromic film method presented here can measure radiation exposures with a precision of ∼ 6% root-mean-square relative error. The intensity profiles have a maximum 25% root-mean-square relative error compared with existing techniques.
  
  
  CONCLUSIONS
  The proposed radiochromic film method for measuring bow tie profiles is an inexpensive (∼$100 USD + film costs), noninvasive method to measure the fan beam intensity profile in CT scanners.
authors.affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Whiting
authors.affiliation: University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15213.
authors.forename: Andreea C
authors.initials: AC
authors.lastname: Dohatcu
authors.affiliation: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298.
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Evans
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri 63110.
authors.forename: David G
authors.initials: DG
authors.lastname: Politte
authors.affiliation: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298.
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Williamson
mesh_terms: D005373:Film Dosimetry / Q000379:methods*; D012399:Rotation; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*