FALLOUT FROM CHERNOBYL AND INCIDENCE OF CHILDHOOD LEUKEMIA IN FINLAND, 1976-92

Objective-To assess effects of fallout from Chernobyl on incidence of childhood leukaemia in Finland. Design-Nationwide cohort study. Extern al exposure measured for 455 Finnish municipalities with instruments d riven 19000 km throughout the country. Values specific to municipaliti es corrected for shielding due to houses and fallout from A bomb testi ng. Internal exposure estimated from whole body measurements on a rand om sample of 81 children. Mean effective dose for two years after inci dent calculated from these measurements. Data on childhood leukaemia o btained from Finnish cancer registry and verified through hospitals tr eating childhood cancers. Setting-Finland, one of the countries most h eavily contaminated by the Chernobyl accident; the population was divi ded into fifths by exposure. Subjects-Children aged 0-14 years in 1976 -92. Main outcome measures-Standardised incidence ratio of childhood l eukaemia and relative excess risk of childhood leukaemia per mSv. From incidence data of Finnish cancer registry for 1976-85, expected numbe rs specific to sex and age group (0-4, 5-9, and 10-14 years) were calc ulated for each municipality for three periods (1976-85, 1986-8, and 1 989-92) and pooled as exposure fifths. Dose response was estimated as regression slope of standardised incidence ratios on mean doses for fi fths for each period. Results-Population weighted mean effective doses for first two years after the accident were 410 mu Sv for the whole c ountry and 970 mu Sv for the population fifth with the highest dose. I n all Finland the incidence of childhood leukaemia did not increase 19 76-92. The relative excess risk 1989-92 was not significantly differen t from zero (7% per mSv; 95% confidence interval -27% to 41%).Conclusi ons-An important increase in childhood leukaemia can be excluded. Any effect is smaller than eight extra cases per million children per year in Finland. The results are consistent with the magnitude of effect e xpected.