Thyroid cancer among children and adolescents in Russia following the Chernobyl accident. Retrospective estimation of thyroid doses and case - control study

The first large-scale study of thyroid cancer among young people in Russia following the Chernobyl accident was conducted. The study population consists of all children and adolescents (17 years and less) who were resided in Kaluga, Orel and Tula oblasts of Russia at the time of Chernobyl accident. Kaluga, Orel and Tula oblasts are approximately equally contaminated oblasts of Russia (up to 15 Ci/km2 for cesium-137). All prevalent and new carcinoma cases from 1 January 1992 to 31 December 1998 were collected in 1997-1998 years as a result of joint project on thyroid disease conducted by the Medical Radiological Research Center (Russia), International Agency for Research on Cancer (France) and Sasakawa Memorial Health Foundation (Japan). Cases of thyroid cancer were found through the Russia National Medical and Dosimetric Registry and Russian Oncology Dispensaries. All cases were independently hystologically verified by the international panel of pathologists from Russia, Belarus and Europe. There were 12 cases in Kaluga, 27 cases in Orel and 23 cases in Tula oblasts. For each case were randomly selected two and four controls: two controls were matched on age, sex and on settlement of residence at the time of accident; four controls were matched on age, sex and on oblast of residence at the time of accident. Each patient and corresponding controls were examinated by the high-resolution ultrasonographic instrument and were interviewed by special trained medical staff. The new technique for reconstruction of the individual dose of internal irradiation of thyroid with incorporated 131I was developed. The method allows to take into account major factors influencing formation thyroid doses of the population: (1) three sources of receipt 131I in organism of the man: inhalation, consumption of milk and green vegetables; (2) types of food production: public and private (individual) sectors of its (her) manufacture; (3) weather conditions of spring of 1986 in regions of residing of the population for determining the dynamic contamination of milk and greens; (4) multichamber model of the dairy for the 'Russian' cow adjusted on direct experimental data; (5) standard age dependent multichamber ICRP model of the man; (6) the data from the special questionnaire about changes of his (her) diet, origination of the meal and his (her) migration during May - July 1986; (7) results of reconstruction on the basis of direct thyroid radiometry for 28229 persons in Kaluga oblast and for 2967 persons in Bryansk oblast. The results of Odds Ratio, Relative Risk and Excess Relative Risk evaluations are discussed for the 1:2 matched case-control study and for the 1:4 matched case- control study. These two methods allow for different information on person's residence at the time of Chernobyl accident and bring out different results for risk evaluation. (author)