title: Cumulative sum quality control for calibrated breast density measurements.
abstract: OBJECTIVE
  Breast density is a significant breast cancer risk factor. Although various methods are used to estimate breast density, there is no standard measurement for this important factor. The authors are developing a breast density standardization method for use in full field digital mammography (FFDM). The approach calibrates for interpatient acquisition technique differences. The calibration produces a normalized breast density pixel value scale. The method relies on first generating a baseline (BL) calibration dataset, which required extensive phantom imaging. Standardizing prospective mammograms with calibration data generated in the past could introduce unanticipated error in the standardized output if the calibration dataset is no longer valid.
  
  
  METHODS
  Sample points from the BL calibration dataset were imaged approximately biweekly over an extended timeframe. These serial samples were used to evaluate the BL dataset reproducibility and quantify the serial calibration accuracy. The cumulative sum (Cusum) quality control method was used to evaluate the serial sampling.
  
  
  RESULTS
  There is considerable drift in the serial sample points from the BL calibration dataset that is x-ray beam dependent. Systematic deviation from the BL dataset caused significant calibration errors. This system drift was not captured with routine system quality control measures. Cusum analysis indicated that the drift is a sign of system wear and eventual x-ray tube failure.
  
  
  CONCLUSIONS
  The BL calibration dataset must be monitored and periodically updated, when necessary, to account for sustained system variations to maintain the calibration accuracy.
authors.affiliation: Cancer Prevention and Control Division, Moffitt Cancer Center, 12902 Magnolia Drive, Tampa, Florida 33612, USA. john.heine@moffitt.org
authors.forename: John J
authors.initials: JJ
authors.lastname: Heine
authors.forename: Ke
authors.initials: K
authors.lastname: Cao
authors.forename: Craig
authors.initials: C
authors.lastname: Beam
mesh_terms: D000273:Adipose Tissue / Q000166:cytology / Q000000981:diagnostic imaging / Q000473:pathology; D001940:Breast / Q000166:cytology*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D002138:Calibration; D008327:Mammography / Q000379:methods* / Q000592:standards*; D008982:Molybdenum; D011786:Quality Control; D012238:Rhodium; D012307:Risk Factors
chemical_list: D008982:Molybdenum; D012238:Rhodium