title: Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults.
abstract: OBJECTIVE
  To estimate cumulative radiation exposure and lifetime attributable risk (LAR) of radiation-induced cancer from computed tomographic (CT) scanning of adult patients at a tertiary care academic medical center.
  
  
  METHODS
  This HIPAA-compliant study was approved by the institutional review board with waiver of informed consent. The cohort comprised 31,462 patients who underwent diagnostic CT in 2007 and had undergone 190,712 CT examinations over the prior 22 years. Each patient's cumulative CT radiation exposure was estimated by summing typical CT effective doses, and the Biological Effects of Ionizing Radiation (BEIR) VII methodology was used to estimate LAR on the basis of sex and age at each exposure. Billing ICD9 codes and electronic order entry information were used to stratify patients with LAR greater than 1%.
  
  
  RESULTS
  Thirty-three percent of patients underwent five or more lifetime CT examinations, and 5% underwent between 22 and 132 examinations. Fifteen percent received estimated cumulative effective doses of more than 100 mSv, and 4% received between 250 and 1375 mSv. Associated LAR had mean and maximum values of 0.3% and 12% for cancer incidence and 0.2% and 6.8% for cancer mortality, respectively. CT exposures were estimated to produce 0.7% of total expected baseline cancer incidence and 1% of total cancer mortality. Seven percent of the cohort had estimated LAR greater than 1%, of which 40% had either no malignancy history or a cancer history without evidence of residual disease.
  
  
  CONCLUSIONS
  Cumulative CT radiation exposure added incrementally to baseline cancer risk in the cohort. While most patients accrue low radiation-induced cancer risks, a subgroup is potentially at higher risk due to recurrent CT imaging.
authors.affiliation: Department of Radiology and Center for Evidence Based Imaging, Brigham and Women's Hospital, 75 Francis St, Boston, MA 02115, USA. asodickson@partners.org
authors.forename: Aaron
authors.initials: A
authors.lastname: Sodickson
authors.forename: Pieter F
authors.initials: PF
authors.lastname: Baeyens
authors.forename: Katherine P
authors.initials: KP
authors.lastname: Andriole
authors.forename: Luciano M
authors.initials: LM
authors.lastname: Prevedello
authors.forename: Richard D
authors.initials: RD
authors.lastname: Nawfel
authors.forename: Richard
authors.initials: R
authors.lastname: Hanson
authors.forename: Ramin
authors.initials: R
authors.lastname: Khorasani