Objective: To assess effects of fallout from Chernobyl on incidence of childhood leukaemia in Finland.
Design: Nationwide cohort study. External exposure measured for 455 Finnish municipalities with instruments driven 19,000 km throughout the country. Values specific to municipalities corrected for shielding due to houses and fallout from A bomb testing. Internal exposure estimated from whole body measurements on a random sample of 81 children. Mean effective dose for two years after incident calculated from these measurements. Data on childhood leukaemia obtained from Finnish cancer registry and verified through hospitals treating childhood cancers.
Setting: Finland, one of the countries most heavily contaminated by the Chernobyl accident; the population was divided into fifths by exposure.
Subjects: Children aged 0-14 years in 1976-92.
Main outcome measures: Standardised incidence ratio of childhood leukaemia and relative excess risk of childhood leukaemia per mSv. From incidence data of Finnish cancer registry for 1976-85, expected numbers specific to sex and age group (0-4, 5-9, and 10-14 years) were calculated for each municipality for three periods (1976-85, 1986-8, and 1989-92) and pooled as exposure fifths. Dose response was estimated as regression slope of standardised incidence ratios on mean doses for fifths for each period.
Results: Population weighted mean effective doses for first two years after the accident were 410 microSv for the whole country and 970 microSv for the population fifth with the highest dose. In all Finland the incidence of childhood leukaemia did not increase 1976-92. The relative excess risk 1989-92 was not significantly different from zero (7% per mSv; 95% confidence interval -27% to 41%).
Conclusions: 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 expected.
PIP: The objective of a nationwide cohort study was to assess the effects of fallout from Chernobyl on the incidence of childhood leukemia in Finland, one of the countries most heavily contaminated by the Chernobyl accident. External exposure was measured with instruments driven by car 19,000 km throughout 455 Finnish municipalities, where the population was divided into fifths by exposure. Values specific to municipalities were corrected for shielding due to houses and fallout from A-bomb testing. Internal exposure estimated from whole body measurements on a random sample of 81 children aged 0-14 years during 1976-1992 and 5-15 in June, 1986, and April, 1988. Mean effective doses from cesium-134 and cesium-137 for 2 years after the incident were calculated from these measurements. Data on childhood leukemia cases that had occurred in children aged 0-14 years during 1975-1992 were obtained from the Finnish cancer registry and verified through each of the 5 university hospitals treating childhood leukemia. Standardized incidence ratio of childhood leukemia and relative excess risk of childhood leukemia per milli sievert (mSv) was measured. From incidence data of the Finnish cancer registry for 1976-1985, expected numbers specific to sex and age group (0-4, 5-9, and 10-14 years) were calculated for each municipality for 3 periods (1976-85, 1986-8, and 1989-92) and pooled as exposure fifths. Dose response was estimated as regression slope of standardized incidence ratios on mean doses for fifths for each period. Population-weighted mean effective doses for first 2 years after the accident were 410 micro Sv for the whole country and 970 micro Sv for the population fifth with the highest dose. In all Finland, the incidence of childhood leukemia did not increase during 1976-1992. The relative excess risk 1989-1992 was not significantly different from zero (7% per mSv; 95% confidence interval -27% to 41%). An important increase in childhood leukemia can be excluded. Any effect is smaller than 8 extra cases per million children per year in Finland.