CHERNOBYL-RELATED THYROID-CANCER - WHAT EVIDENCE FOR ROSE OF SHORT-LIVED IODINES

Over 500 cases of thyroid cancer were diagnosed in Belarus between 198 6 and 1995 among persons exposed as-children (under 15 years of age) t o radioactive contamination from the Chernobyl nuclear accident. There is little doubt that radioactive iodine isotopes emitted during the n uclear explosion and subsequent fire were instrumental in causing mali gnancy in this particular organ. Comparison of the observed geographic distribution of Chernobyl-associated thyroid cancer incidence rates b y districts with contamination maps of radioactive fallout shows a bet ter fit for estimated I-131 contamination than for Cs-137. Because I-1 31 used for medical purposes had not been considered carcinogenic in h umans in the past, and in view of the unusually short latency period b etween exposure and clinical manifestation of cancer, it is suspected that not only I-131 but also energy-rich shorter-lived radioiodines ma y have played a role in post-Chernobyl thyroid carcinogenesis. Measure ments of iodine isotopes are not available, but reconstruction of geog raphic distributions and estimations of radioactive fallout based on m eteorological observations immediately following the accident could pr ovide a basis for comparison with the distribution of thyroid cancer c ases. In this paper; data from the Epidemiological Cancer Register for Belarus will be used to show geographic and time trends of thyroid ca ncer incidence rates in the period from 1986 to 1995 among persons who were exposed as children, and these will be compared with the estimat ed contamination by radioiodines. Tentative conclusions are drawn from the available evidence and further research requirements discussed.