title: A quantitative comparison of data evaluation methods to derive diagnostic reference levels for CT from a dosimetric survey: correlation analysis compared to simple evaluation strategies.
abstract: OBJECTIVE
  To compare simple and sophisticated evaluation strategies for CT dosimetry surveys with focus on DRLs.
  
  
  METHODS
  Based on data from a nationwide Austrian CT dose survey, different evaluation strategies are compared. These were pooled data analysis, weight banding excluding data from patients with weights outside ±20 kg of the standard weights (70 and 75.6 kg representing the actual average weight), and a regression method estimating DLP probability distributions for the standard patient for each scanner before calculating quartiles.
  
  
  RESULTS
  In the abdomen and chest region, weight restriction (-9% and -4% around 70 and 75.6 kg, respectively, compared to pooled data analysis) and statistically weighting each scanner equally (-9%) have the largest effect on DRLs derived. However, the difference in 3rd quartiles calculated using weight restriction alone compared to regression analysis is relatively small (<1% for 70 ± 20 and -6% for 75.6 ± 20 kg, respectively, trunk region). In the head/neck region the effect of weight restriction is less than in for scans of the trunk (-1.3% and -0.2%, respectively); the most prominent changes resulted from excluding scanners with less than 10 patient cases (-5%), and equally weighting scanners rather than cases (-3%).
  
  
  CONCLUSIONS
  For adult CT examinations (different to a paediatric survey), quite simple evaluation strategies yield results very comparable to those from sophisticated strategies.
authors: Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20/4L, 1090 Vienna, Austria.
authors: Robert
authors: R
authors: Leithner
authors: Peter
authors: P
authors: Homolka
mesh_terms: D000328:Adult; D003625:Data Collection; D006801:Humans; D009928:Organ Specificity; D011874:Radiometry; D012015:Reference Standards; D014057:Tomography, X-Ray Computed / Q000592:standards*
keywords: 84; DRL; Diagnostic radiology; Diagnostic reference levels; Patient dose; Radiation protection