Morbidity of Chernobyl Nuclear Power Plant Accident Clean - up Workers with Oncological Diseases from 1990 to 2004

The world's largest ever radiation accident involving a nuclear reactor occurred on 26 April 1986 at the Chernobyl nuclear power plant (CNPP). More than 6 000 Latvian inhabitants worked to clean-up CNPP accident in 1986-1991. The duration of accident clean-up workers exposure was from few weeks to 6 months, including external as well as internal radiation. The estimated external radiation doses were 0,01-0,5 Gy. Latvian CNPP accident clean-up workers State register was created on the basis of the Center of Occupational and Radiological medicine of P. Stradins Clinical University hospital in 1994 but examination of clean-up workers was started in 1986. Our aim was to analyse oncological morbidity in clean-up workers in comparison with oncological morbidity in Latvian men population. Materials and methods. For analysis of oncological morbidity in NPP accident clean-up workers, the data of Latvian CNPP accident clean-up workers State Register were used. The group for investigation includes 4053 males what were examined regularly (in average 1600 persons every year) from 1998 to 2004. From these groups of clean-up workers we have revealed 177 persons with oncological diseases over the observation period. Among them only two women but others were men. We have used for the comparison of oncological morbidity data of Latvian Cancer registry and Central bureau of statistics. Summary morbidity with oncological diseases and morbidity with oncological diseases of prostata, stomach, lungs and thyroid for men who have taken part in clean-up works were analysed. Oncological morbidity in age group 35-69 years over the observation period 1998-2004 were compared With age-matched non-exposed population morbidity. Results and discussion. In the structure of oncological morbidity of the Chernobyl accident clean-up workers over the period 1990-2004 in the first place was lung cancer, in the second place -stomach cancer, in the third place -prostate cancer. CNPP clean-up worker's common oncological morbidity in the age group 35-69 years over the observation period 1998-2004 is a little higher in comparison with age-matched non-exposed men population morbidity. Morbidity with thyroid cancer is 10 times higher, morbidity with prostate cancer - 9, but with ventriculi cancer 4. times higher than in population. The increase of oncological diseases for clean-up workers was over the observation period 1998-2000 and in 2003. Incidence of morbidity with oncological diseases of prostate has trend for progression during last 5 years. Maximal increase of incidence in clean-up workers was in age group till 60 years but in population - after 60 years. Thyroid cancer presents a special case, as the thyroid concentrates iodines and much of the radioactivity released from the damaged reactor was in the form of radioiodines; thus thyroid exposures could have come from internally deposited radioiodines as well as from external radiation. Based on studies of other population exposed to low-dose radiation latent period of radiation -induced oncological diseases could be 8-30 years. Conclusion. Oncological morbidity of Chernobyl NPP accident clean-up workers during 1990-2004 is progressively increasing. Increase of incidence of oncological diseases of thyroid gland, prostate and stomach is higher than that among age and sex matched group of Latvia's population. Research on development of oncological diseases of clean-up workers exposed by low-dose radiation needs further research. (authors)