Results of the US-Ukrainian Study of Leukemia and Related Disorders Among Chernobyl Cleanup Workers

Leukemia is one of the early cancers induced by ionizing radiation. Following the Chornobyl accident in Ukraine in April 1986, several hundred thousand workers received fractionated exposure, primarily from external gamma radiation. A nested case-control study of leukemia was performed in a cohort of 110,645 cleanup workers identified from the Chornobyl State Registry of Ukraine during the period 1986 to 2000. A provisional computerized registry of leukemia and 99 related hematological disorders was created through an intensive search of the files of the oncology, hematology and pathology departments within the study area encountering 37,605 possible cases. After linkage and case ascertainment by the international hematology review 111 cases were confirmed as leukemia (87), multiple myeloma (8) and MDS (7). 66.6% of cases and 7.1% of selected controls were deceased. Individual bone marrow doses were estimated using RADRUE method enabling dose reconstruction from the interviews carried out with proxy respondents. Two types of proxies were selected for each deceased subject: a spouse or next-of-kin proxy to provide data on demographic factors and medical history, and to propose co-workers who could serve as proxy respondents regarding the deceased subjects work history. Detailed interviews were conducted and in 71 case and 501 age- and residence-matched controls selected from the same cohort (mean dose=76.4 (SD=213.4) mGy). In order to reduce uncertainties in the dose estimates, a series of validation studies was undertaken. Conditional logistic regression to estimate leukemia risks. The excess relative risk of total leukemia was 3.44 per Gy (95% confidence interval 0.47 9.78, p<0.01). The dose-response was linear and did not significantly differ by calendar period of first work in the 30-km Chornobyl zone, duration or type of work. A similar dose-response relationship was found for chronic and non-chronic lymphocytic leukemia

Cataracts among Chernobyl clean-up workers: implications regarding permissible eye exposures

The eyes of a prospective cohort of 8,607 Chernobyl clean-up workers (liquidators) were assessed for cataract at 12 and 14 years after exposure. The prevalence of strictly age-related cataracts was low, as expected (only 3.9% had nuclear cataracts at either examination), since 90% of the cohort was younger than 55 years of age at first examination. However, posterior subcapsular or cortical cataracts characteristic of radiation exposure were present in 25% of the subjects. The data for Stage 1 cataracts, and specifically for posterior subcapsular cataracts, revealed a significant dose response. When various cataract end points were analyzed for dose thresholds, the confidence intervals all excluded values greater than 700 mGy. Linear-quadratic dose-response models yielded mostly linear associations, with weak evidence of upward curvature. The findings do not support the ICRP 60 risk guideline assumption of a 5-Gy threshold for "detectable opacities" from protracted exposures but rather point to a dose-effect threshold of under 1 Gy. Thus, given that cataract is the dose-limiting ocular pathology in current eye risk guidelines, revision of the allowable exposure of the human visual system to ionizing radiation should be considered

Dosimetry for a study of low-dose radiation cataracts among Chernobyl clean-up workers

A cohort of 8,607 Ukrainian Chernobyl clean-up workers during 1986-1987 was formed to study cataract formation after ionizing radiation exposure. Study eligibility required the availability of sufficient exposure information to permit the reconstruction of doses to the lens of the eye. Eligible groups included civilian workers, such as those who built the "sarcophagus" over the reactor, Chernobyl Nuclear Power Plant Workers, and military reservists who were conscripted for clean-up work. Many of the official doses for workers were estimates, because only a minority wore radiation badges. For 106 military workers, electron paramagnetic resonance (EPR) measurements of extracted teeth were compared with the recorded doses as the basis to adjust the recorded gamma-ray doses and provide estimates of uncertainties. Beta-particle doses to the lens were estimated with an algorithm devised to take into account the nature and location of Chernobyl work, time since the accident, and protective measures taken. A Monte Carlo routine generated 500 random estimates for each individual from the uncertainty distributions of the gamma-ray dose and of the ratio of beta-particle to gamma-ray doses. The geometric mean of the 500 combined beta-particle and gamma-ray dose estimates for each individual was used in the data analyses. The median estimated lens dose for the cohort was 123 mGy, while 4.4% received >500 mGy