A cohort study of thyroid cancer and other thyroid diseases after the chornobyl accident: thyroid cancer in Ukraine detected during first screening.
BACKGROUND
The Chornobyl accident in 1986 exposed thousands of people to radioactive iodine isotopes, particularly (131)I; this exposure was followed by a large increase in thyroid cancer among those exposed as children and adolescents, particularly in Belarus, the Russian Federation, and Ukraine. Here we report the results of the first cohort study of thyroid cancer among those exposed as children and adolescents following the Chornobyl accident.


METHODS
A cohort of 32 385 individuals younger than 18 years of age and resident in the most heavily contaminated areas in Ukraine at the time of the accident was invited to be screened for any thyroid pathology by ultrasound and palpation between 1998 and 2000; 13 127 individuals (44%) were actually screened. Individual estimates of radiation dose to the thyroid were available for all screenees based on radioactivity measurements made shortly after the accident and on interview data. The excess relative risk per gray (Gy) was estimated using individual doses and a linear excess relative risk model.


RESULTS
Forty-five pathologically confirmed cases of thyroid cancer were found during the 1998-2000 screening. Thyroid cancer showed a strong, monotonic, and approximately linear relationship with individual thyroid dose estimate (P<.001), yielding an estimated excess relative risk of 5.25 per Gy (95% confidence interval [CI] = 1.70 to 27.5). Greater age at exposure was associated with decreased risk of radiation-related thyroid cancer, although this interaction effect was not statistically significant.


CONCLUSIONS
Exposure to radioactive iodine was strongly associated with increased risk of thyroid cancer among those exposed as children and adolescents. In the absence of Chornobyl radiation, 11.2 thyroid cancer cases would have been expected compared with the 45 observed, i.e., a reduction of 75% (95% CI = 50% to 93%). The study also provides quantitative risk estimates minimally confounded by any screening effects. Caution should be exercised in generalizing these results to any future similar accidents because of the potential differences in the nature of the radioactive iodines involved, the duration and temporal patterns of exposures, and the susceptibility of the exposed population.
Tronko
Mykola D
MD
Institute of Endocrinology and Metabolism, Kyiv, Ukraine.
Howe
Geoffrey R
GR
Bogdanova
Tetyana I
TI
Bouville
Andre C
AC
Epstein
Ovsiy V
OV
Brill
Aaron B
AB
Likhtarev
Illya A
IA
Fink
Daniel J
DJ
Markov
Valentyn V
VV
Greenebaum
Ellen
E
Olijnyk
Valery A
VA
Masnyk
Ihor J
IJ
Shpak
Victor M
VM
McConnell
Robert J
RJ
Tereshchenko
Valery P
VP
Robbins
Jacob
J
Zvinchuk
Oleksandr V
OV
Zablotska
Lydia B
LB
Hatch
Maureen
M
Luckyanov
Nickolas K
NK
Ron
Elaine
E
Thomas
Terry L
TL
Voillequé
Paul G
PG
Beebe
Gilbert W
GW
D000293:Adolescent; D000328:Adult; D047852:Chernobyl Nuclear Accident; D002648:Child; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D004307:Dose-Response Relationship, Radiation; D015340:Epidemiologic Research Design; D005260:Female; D006801:Humans; D015994:Incidence; D007457:Iodine Radioisotopes / Q000009:adverse effects*; D016014:Linear Models; D008297:Male; D008403:Mass Screening; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D016017:Odds Ratio; D015995:Prevalence; D011446:Prospective Studies; D018788:Radioactive Hazard Release; D018570:Risk Assessment; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000453:epidemiology*; D014455:Ukraine / Q000453:epidemiology
D007457:Iodine Radioisotopes