Oncologic morbidity and mortality among emergency workers at the ChNPP: estimation of radiation risks

In this work the problems connected with calculation of indices of oncologic morbidity and mortality on the basis of information about emergency workers at the ChNPP (EWs) accumulated in the Russian National Medical and Dosimetric Registry (RNMDR) over the period from 1986 till the beginning of 1994 are discussed. A short characteristic of the cohort of EWs and the corresponding structure of oncologic morbidity and mortality is given. As of the beginning of 1994 in the RNMDR 159020 EWs were registered, the great majority among them comprised men (about 98%), the age (85%) of which ranges from 20 to 40 years at the moment of arrival to the zone of works around the ChNPP. The cohort of EWs studied in the paper involves 143032 people not have been ill with oncologic diseases before the ChNPP accident and for which the most complete individual information (age, duration of being in the zone of works around the ChNPP and date of arrival to it) and data of medical monitoring were available. Up to 80% of EWs have officially registered dose of external radiation the average value of which approximated 11 cGy. Among 143032 EWs, medico-dosimetric information about which is studied in the work, 1026 cases of oncologic diseases were diagnosed and 341 deaths from malignant neoplasms were registered. The most widespread among them are malignant neoplasms of digestive organs and peritoneum (ICD-9: 150-159) as well as those of respiratory organs and chest (ICD-9: 160-165). Particular emphasis has been placed on determination of relationships between indices of oncomorbidity and mortality and different factors of risk. In particular, availability of statistically significant tendencies (trends) for indices of oncomorbidity and mortality such as functions of age, year of arrival to the zone of works around the ChNPP and external radiation dose is indicated. Age of EWs, external radiation dose and time of arrival to the zone have a great deal to do with indices of morbidity and mortality. Absolute values of morbidity and mortality indices increase with time elapsed after the ChNPP accident. To estimate an effect of radiation factor on the state of health of EWs the coefficients of relative risk were calculated which proved to be significantly dependent on external radiation dose for all oncologic diseases as a whole (ICD-9: 140-208.9). Estimate of the value of excess relative risk per 1 Gy for morbidity from malignant neoplasms is statistically significant and with 95% confidence interval is equal to 1,7 (0,3; 3,1). The analogous index for oncomortality makes up 2,25, at the same time the lower limit of 95% confidence interval of this estimate is in negative field (-0,43; 4,92) what does not allow to make a conclusion about its statistical importance. Based on the data available in the RNMDR as of the beginning of 1994 it is not possible to infer statistically significant lincage of relative risk (both for mortality and morbidity) with age, date of arrival to the zone and duration of being in it.