title: Exposure to ionizing radiation and estimate of secondary cancers in the era of high-speed CT scanning: projections from the Medicare population.
abstract: OBJECTIVE
  The aims of this study were to analyze the distribution and amount of ionizing radiation delivered by CT scans in the modern era of high-speed CT and to estimate cancer risk in the elderly, the patient group most frequently imaged using CT scanning.
  
  
  METHODS
  A retrospective cohort study was conducted using Medicare claims spanning 8 years (1998-2005) to assess CT use. The data were analyzed in two 4-year cohorts, 1998 to 2001 (n = 5,267,230) and 2002 to 2005 (n = 5,555,345). The number and types of CT scans each patient received over the 4-year periods were analyzed to determine the percentage of patients exposed to threshold radiation of 50 to 100 mSv (defined as low) and >100 mSv (defined as high). The National Research Council's Biological Effects of Ionizing Radiation VII models were used to estimate the number of radiation-induced cancers.
  
  
  RESULTS
  CT scans of the head were the most common examinations in both Medicare cohorts, but abdominal imaging delivered the greatest proportion (43% in the first cohort and 40% in the second cohort) of radiation. In the 1998 to 2001 cohort, 42% of Medicare patients underwent CT scans, with 2.2% and 0.5% receiving radiation doses in the low and high ranges, respectively. In the 2002 to 2005 cohort, 50% of Medicare patients received CT scans, with 4.2% and 1.2% receiving doses in the low and high ranges. In the two populations, 1,659 (0.03%) and 2,185 (0.04%) cancers related to ionizing radiation were estimated, respectively.
  
  
  CONCLUSIONS
  Although radiation doses have been increasing along with the increasing reliance on CT scans for diagnosis and therapy, using conservative estimates with worst-case scenario methodology, the authors found that the risk for secondary cancers is low in older adults, the group subjected to the most frequent CT scanning. Trends showing increasing use, however, underscore the importance of monitoring CT utilization and its consequences.
authors.affiliation: Department of Radiology, Stanford University Medical Center, Stanford, California 94305, USA.
authors.forename: Aabed B
authors.initials: AB
authors.lastname: Meer
authors.forename: Pat A
authors.initials: PA
authors.lastname: Basu
authors.forename: Laurence C
authors.initials: LC
authors.lastname: Baker
authors.forename: Scott W
authors.initials: SW
authors.lastname: Atlas
mesh_terms: D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data*; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D015995:Prevalence; D016016:Proportional Hazards Models; D018570:Risk Assessment; D012307:Risk Factors; D017678:Sex Distribution; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*; D014481:United States / Q000453:epidemiology