title: Calibration of GafChromic XR-RV3 radiochromic film for skin dose measurement using standardized x-ray spectra and a commercial flatbed scanner.
abstract: OBJECTIVE
  In this study, newly formulated XR-RV3 GafChromic film was calibrated with National Institute of Standards and Technology (NIST) traceability for measurement of patient skin dose during fluoroscopically guided interventional procedures.
  
  
  METHODS
  The film was calibrated free-in-air to air kerma levels between 15 and 1100 cGy using four moderately filtered x-ray beam qualities (60, 80, 100, and 120 kVp). The calibration films were scanned with a commercial flatbed document scanner. Film reflective density-to-air kerma calibration curves were constructed for each beam quality, with both the orange and white sides facing the x-ray source. A method to correct for nonuniformity in scanner response (up to 25% depending on position) was developed to enable dose measurement with large films. The response of XR-RV3 film under patient backscattering conditions was examined using on-phantom film exposures and Monte Carlo simulations.
  
  
  RESULTS
  The response of XR-RV3 film to a given air kerma depended on kVp and film orientation. For a 200 cGy air kerma exposure with the orange side of the film facing the source, the film response increased by 20% from 60 to 120 kVp. At 500 cGy, the increase was 12%. When 500 cGy exposures were performed with the white side facing the x-ray source, the film response increased by 4.0% (60 kVp) to 9.9% (120 kVp) compared to the orange-facing orientation. On-phantom film measurements and Monte Carlo simulations show that using a NIST-traceable free-in-air calibration curve to determine air kerma in the presence of backscatter results in an error from 2% up to 8% depending on beam quality. The combined uncertainty in the air kerma measurement from the calibration curves and scanner nonuniformity correction was +/- 7.1% (95% C.I.). The film showed notable stability. Calibrations of film and scanner separated by 1 yr differed by 1.0%.
  
  
  CONCLUSIONS
  XR-RV3 radiochromic film response to a given air kerma shows dependence on beam quality and film orientation. The presence of backscatter slightly modifies the x-ray energy spectrum; however, the increase in film response can be attributed primarily to the increase in total photon fluence at the sensitive layer. Film calibration curves created under free-in-air conditions may be used to measure dose from fluoroscopic quality x-ray beams, including patient backscatter with an error less than the uncertainty of the calibration in most cases.
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA.
authors.forename: Bradley P
authors.initials: BP
authors.lastname: McCabe
authors.forename: Michael A
authors.initials: MA
authors.lastname: Speidel
authors.forename: Tina L
authors.initials: TL
authors.lastname: Pike
authors.forename: Michael S
authors.initials: MS
authors.lastname: Van Lysel
mesh_terms: D000388:Air; D002138:Calibration; D003116:Color; D005373:Film Dosimetry / Q000295:instrumentation* / Q000592:standards*; D005471:Fluoroscopy; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D012542:Scattering, Radiation; D012867:Skin / Q000000981:diagnostic imaging / Q000528:radiation effects*; D013057:Spectrum Analysis / Q000592:standards*; D013997:Time Factors; D035501:Uncertainty; D014965:X-Rays