title: External radiation dose and cancer mortality among French nuclear workers: considering potential confounding by internal radiation exposure.
abstract: OBJECTIVE
  French nuclear workers have detailed records of their occupational exposure to external radiation that have been used to examine associations with subsequent cancer mortality. However, some workers were also exposed to internal contamination by radionuclides. This study aims to assess the potential for bias due to confounding by internal contamination of estimates of associations between external radiation exposure and cancer mortality.
  
  
  METHODS
  A cohort of 59,004 workers employed for at least 1 year between 1950 and 1994 by CEA (Commissariat à l'Energie Atomique), AREVA NC, or EDF (Electricité de France) and badge-monitored for external radiation exposure were followed through 2004 to assess vital status and cause of death. A flag based on a workstation-exposure matrix defined four levels of potential for internal contamination. Standardized mortality ratios were assessed for each level of the internal contamination indicator. Poisson regression was used to quantify associations between external radiation exposure and cancer mortality, adjusting for potential internal contamination.
  
  
  RESULTS
  For solid cancer, the mortality deficit tended to decrease as the levels of potential for internal contamination increased. For solid cancer and leukemia excluding chronic lymphocytic leukemia, adjusting the dose-response analysis on the internal contamination indicator did not markedly change the excess relative risk per Sievert of external radiation dose.
  
  
  CONCLUSIONS
  This study suggests that in this cohort, neglecting information on internal dosimetry while studying the association between external dose and cancer mortality does not generate a substantial bias. To investigate more specifically the health effects of internal contamination, an effort is underway to estimate organ doses due to internal contamination.
authors.affiliation: Ionizing Radiation Epidemiology Laboratory, Institute for Radiological Protection and Nuclear Safety, 31 Avenue de la Division Leclerc, BP 17, 92262, Fontenay aux Roses Cedex, France. lucie.fournier@irsn.fr.
authors.forename: L
authors.identifier: http://orcid.org/0000-0002-9414-9249
authors.initials: L
authors.lastname: Fournier
authors.affiliation: Ionizing Radiation Epidemiology Laboratory, Institute for Radiological Protection and Nuclear Safety, 31 Avenue de la Division Leclerc, BP 17, 92262, Fontenay aux Roses Cedex, France.
authors.forename: O
authors.initials: O
authors.lastname: Laurent
authors.affiliation: Ionizing Radiation Epidemiology Laboratory, Institute for Radiological Protection and Nuclear Safety, 31 Avenue de la Division Leclerc, BP 17, 92262, Fontenay aux Roses Cedex, France.
authors.forename: E
authors.initials: E
authors.lastname: Samson
authors.affiliation: Ionizing Radiation Epidemiology Laboratory, Institute for Radiological Protection and Nuclear Safety, 31 Avenue de la Division Leclerc, BP 17, 92262, Fontenay aux Roses Cedex, France.
authors.forename: S
authors.initials: S
authors.lastname: Caër-Lorho
authors.affiliation: AREVA, Paris, France.
authors.forename: P
authors.initials: P
authors.lastname: Laroche
authors.affiliation: EDF, Saint Denis, France.
authors.forename: B
authors.initials: B
authors.lastname: Le Guen
authors.affiliation: Ionizing Radiation Epidemiology Laboratory, Institute for Radiological Protection and Nuclear Safety, 31 Avenue de la Division Leclerc, BP 17, 92262, Fontenay aux Roses Cedex, France.
authors.forename: D
authors.initials: D
authors.lastname: Laurier
authors.affiliation: Ionizing Radiation Epidemiology Laboratory, Institute for Radiological Protection and Nuclear Safety, 31 Avenue de la Division Leclerc, BP 17, 92262, Fontenay aux Roses Cedex, France.
authors.forename: K
authors.initials: K
authors.lastname: Leuraud
mesh_terms: D000328:Adult; D015331:Cohort Studies; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D005602:France; D006801:Humans; D007953:Leukemia, Radiation-Induced / Q000209:etiology; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000209:etiology / Q000401:mortality*; D055848:Nuclear Power Plants; D009784:Occupational Diseases / Q000209:etiology / Q000401:mortality*; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis*; D016012:Poisson Distribution; D000069079:Radiation Exposure / Q000009:adverse effects / Q000032:analysis*; D011874:Radiometry / Q000379:methods; D012044:Regression Analysis
keywords: Confounding; Internal contamination; Nuclear workers; Occupational epidemiology