title: Frequency of undetected thyroid nodules in a large I-131-exposed population repeatedly screened by ultrasonography: results from the Ukrainian-American cohort study of thyroid cancer and other thyroid diseases following the Chornobyl accident.
abstract: BACKGROUND
  Imperfect detection on screening tests can lead to erroneous conclusions about the natural history of thyroid nodules following radiation exposure. Our objective was to assess in a repeatedly screened I-131-exposed population the frequency with which a thyroid nodule could be retrospectively identified on ultrasonography studies preceding the one on which it was initially detected.
  
  
  METHODS
  A cohort of over 13,000 young people exposed to fallout from Chornobyl underwent ultrasonography screening at 2-year intervals from 1998 to 2007. The study group consisted of screening examinations on which a thyroid nodule was detected following one or more prior negative examinations. In the study group there were 48 cancers and 92 benign nodules. For each of these 140 index studies a comparison set was created containing all available prior studies plus (to test for bias) negative studies from control subjects. While viewing the index study, three independent reviewers scored the comparison studies for the presence and size of a preexisting nodule. Detection rates were compared for true priors versus controls, for cancer versus benign, and for histologic subtypes of papillary carcinoma.
  
  
  RESULTS
  A preexisting nodule was identified by at least one reviewer in 24.0% of the true prior versus 8.3% of the controls and by all three reviewers in 11% versus 1% (Fisher's exact test, p < 0.0001). There was no significant difference in detection rates between cancers and benign nodules (22.4% vs. 24.7%, p = 0.411). There was no correlation between time from prior to index study and change in nodule size for either malignant or benign nodules (r = 0.01, NS). There were no differences in detection rates or size among papillary cancer subtypes. Reviewers could not distinguish between true priors and controls.
  
  
  CONCLUSIONS
  These findings, showing significant rates of undetected benign and malignant nodules and no evidence for rapid growth, suggest that conclusions drawn from screening studies about the frequency of late-developing, rapidly growing thyroid nodules following radiation exposure should be interpreted with caution.
authors.affiliation: Radiology Department, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania 19107, USA. patrick.okane@jefferson.edu
authors.forename: Patrick
authors.initials: P
authors.lastname: O'Kane
authors.forename: Evgeniy
authors.initials: E
authors.lastname: Shelkovoy
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McConnell
authors.forename: Victor
authors.initials: V
authors.lastname: Shpak
authors.forename: Laurence
authors.initials: L
authors.lastname: Parker
authors.forename: Alina
authors.initials: A
authors.lastname: Brenner
authors.forename: Lydia
authors.initials: L
authors.lastname: Zablotska
authors.forename: Mykola
authors.initials: M
authors.lastname: Tronko
authors.forename: Maureen
authors.initials: M
authors.lastname: Hatch
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000000981:diagnostic imaging / Q000453:epidemiology; D000293:Adolescent; D000328:Adult; D018276:Carcinoma, Medullary / Q000000981:diagnostic imaging / Q000453:epidemiology; D002291:Carcinoma, Papillary / Q000000981:diagnostic imaging / Q000453:epidemiology; D047852:Chernobyl Nuclear Accident; D002648:Child; D015331:Cohort Studies; D004781:Environmental Exposure; D006801:Humans; D007457:Iodine Radioisotopes / Q000633:toxicity*; D008137:Longitudinal Studies; D008297:Male; D009381:Neoplasms, Radiation-Induced / Q000000981:diagnostic imaging / Q000453:epidemiology; D013959:Thyroid Diseases / Q000000981:diagnostic imaging / Q000453:epidemiology; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging / Q000453:epidemiology; D016606:Thyroid Nodule / Q000000981:diagnostic imaging / Q000453:epidemiology*; D014455:Ukraine / Q000208:ethnology; D014463:Ultrasonography; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes