Following the accident at the Chernobyl nuclear powerplant on 26 April 1986, radioactive materials were deposited over large areas of Europe.
Outside the immediate vicinity of the accident, the predicted health effects due to radiation are rather small. Nevertheless, these health effects should be monitored.
Childhood leukaemia is the most logical choice of adverse health effect for monitoring. Radiation induced leukaemias appear early (2 to 10 years) after exposure, and provide the largest excess incidence of any cancer.
The study involves the collection of data on all recorded cases of childhood leukaemia and lymphoma occurring in the populations covered by the registries.
The period 1980 to 1985 will serve as a baseline to investigate differences in the incidence between regions, and to provide information on underlying trends in incidence in the 6 years preceding the accident. Changes in 1986 and subsequent years will be studied to see if they bear any relationship to the estimated exposure levels in different regions.
Preliminary results confirm the rather constant background incidence of leukaemia, around 40 per million children per year. There is a slight male preponderance in almost all countries. Time trends in 1980 to 1985 are rather variable in different countries, but several show small increases in incidence, against which future changes (postaccident) will have to be evaluated.
A first complete analysis of background incidence, and age specific incidence rates in 1986 to 1987 will be completed during 1990. However, it is too early to relate any of the incidence data to the exposure estimates. Future analyses will also examine birth cohort specific incidence, with particular interest focussed on children born in May 1986 to January 1987 (prenatal exposure).
A summary of scientific background to the study and of progress to date was presented at the 9th Conference of the American Statistical Association on Radiation and Health, in Colorado, USA (8 to 12 July 1990). Since the previous progress report (9th November 1989) the following changes should be noted:
Data collection for the period 1980 to 1987 is almost complete.
Incidence rates for the period 1980 to 1985 have been calculated, also those for 1986 and 1987, for national populations.
The definition of the subnational areas for which UNSCEAR has calculated dose estimates are now available. Incidence rates for these subdivisions have yet to be calculated.
The participation of Bulgaria in the ECLIS study has been agreed. The quality of available data, and the requirements related to verifying registrations against clinical records remain to be defined.
Data have been promised from those parts of the USSR most affected by the accident. However, there remain unquantified problems in the validation of any routine statistical data from areas without a comprehensive population-based cancer registry. A separate contract may be required for any comprehensive study within the USSR.