title: Relationship between paediatric CT scans and subsequent risk of leukaemia and brain tumours: assessment of the impact of underlying conditions.
abstract: BACKGROUND
  We previously reported evidence of a dose-response relationship between ionising-radiation exposure from paediatric computed tomography (CT) scans and the risk of leukaemia and brain tumours in a large UK cohort. Underlying unreported conditions could have introduced bias into these findings.
  
  
  METHODS
  We collected and reviewed additional clinical information from radiology information systems (RIS) databases, underlying cause of death and pathology reports. We conducted sensitivity analyses excluding participants with cancer-predisposing conditions or previous unreported cancers and compared the dose-response analyses with our original results.
  
  
  RESULTS
  We obtained information from the RIS and death certificates for about 40% of the cohort (n∼180 000) and found cancer-predisposing conditions in 4 out of 74 leukaemia/myelodysplastic syndrome (MDS) cases and 13 out of 135 brain tumour cases. As these conditions were unrelated to CT exposure, exclusion of these participants did not alter the dose-response relationships. We found evidence of previous unreported cancers in 2 leukaemia/MDS cases, 7 brain tumour cases and 232 in non-cases. These previous cancers were related to increased number of CTs. Exclusion of these cancers reduced the excess relative risk per mGy by 15% from 0.036 to 0.033 for leukaemia/MDS (P-trend=0.02) and by 30% from 0.023 to 0.016 (P-trend<0.0001) for brain tumours. When we included pathology reports we had additional clinical information for 90% of the cases. Additional exclusions from these reports further reduced the risk estimates, but this sensitivity analysis may have underestimated risks as reports were only available for cases.
  
  
  CONCLUSIONS
  Although there was evidence of some bias in our original risk estimates, re-analysis of the cohort with additional clinical data still showed an increased cancer risk after low-dose radiation exposure from CT scans in young patients.
authors.affiliation: Radiation Epidemiology Unit, Division of Cancer Epidemiology and Genetics, NCI, Bethesda, MD, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Berrington de Gonzalez
authors.affiliation: Institute of Health and Society, Newcastle University, Sir James Spence Institute, Royal Victoria Infirmary, Newcastle upon Tyne NE1 4LP, UK.
authors.forename: Jane A
authors.initials: JA
authors.lastname: Salotti
authors.affiliation: Great Ormond Street Hospital for Children NHS Trust, London WC1N 3JH, UK.
authors.forename: Kieran
authors.initials: K
authors.lastname: McHugh
authors.affiliation: Radiation Epidemiology Unit, Division of Cancer Epidemiology and Genetics, NCI, Bethesda, MD, USA.
authors.forename: Mark P
authors.initials: MP
authors.lastname: Little
authors.affiliation: Institute of Health and Society, Newcastle University, Sir James Spence Institute, Royal Victoria Infirmary, Newcastle upon Tyne NE1 4LP, UK.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Harbron
authors.affiliation: Radiation Epidemiology Unit, Division of Cancer Epidemiology and Genetics, NCI, Bethesda, MD, USA.
authors.forename: Choonsik
authors.initials: C
authors.lastname: Lee
authors.affiliation: Radiation Epidemiology Unit, Division of Cancer Epidemiology and Genetics, NCI, Bethesda, MD, USA.
authors.forename: Estelle
authors.initials: E
authors.lastname: Ntowe
authors.affiliation: Radiation Epidemiology Unit, Division of Cancer Epidemiology and Genetics, NCI, Bethesda, MD, USA.
authors.forename: Melissa Z
authors.initials: MZ
authors.lastname: Braganza
authors.affiliation: Departments of Medicine and Paediatrics, Population Cancer Research Program, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Louise
authors.initials: L
authors.lastname: Parker
authors.affiliation: Radiation Epidemiology Unit, Division of Cancer Epidemiology and Genetics, NCI, Bethesda, MD, USA.
authors.forename: Preetha
authors.initials: P
authors.lastname: Rajaraman
authors.affiliation: New College, University of Oxford, Oxford, UK.
authors.forename: Charles
authors.initials: C
authors.lastname: Stiller
authors.affiliation: Radiation Epidemiology Unit, Division of Cancer Epidemiology and Genetics, NCI, Bethesda, MD, USA.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Stewart
authors.affiliation: Institute of Health and Society, Newcastle University, Sir James Spence Institute, Royal Victoria Infirmary, Newcastle upon Tyne NE1 4LP, UK.
authors.forename: Alan W
authors.initials: AW
authors.lastname: Craft
authors.affiliation: Institute of Health and Society, Newcastle University, Sir James Spence Institute, Royal Victoria Infirmary, Newcastle upon Tyne NE1 4LP, UK.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Pearce
mesh_terms: D000293:Adolescent; D000328:Adult; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007938:Leukemia / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D009381:Neoplasms, Radiation-Induced / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000009:adverse effects / Q000706:statistics & numerical data*; D055815:Young Adult