Lessons from past radiation accidents: Critical review of methods addressed to individual dose assessment of potentially exposed people and integration with medical assessment.

The experiences of the Chernobyl and Fukushima nuclear accidents showed that dosimetry was the essential tool in the emergency situation for decision making processes, such as evacuation and application of protective measures. However, at the consequent post-accidental phases, it was crucial also for medical health surveillance and in further adaptation to changed conditions with regards to radiation protection of the affected populations. This review provides an analysis of the experiences related to the role of dosimetry (dose measurements, assessment and reconstruction) regarding health preventive measures in the post-accidental periods on the examples of the major past nuclear accidents such as Chernobyl and Fukushima. Recommendations derived from the review are called to improve individual dose assessment in case of a radiological accident/incident and should be considered in advance as guidelines to follow for having better information. They are given as conclusions.

Analysis of the association between ionizing radiation and mortality in uranium workers from five plants involved in the nuclear fuel production cycle in France.

PURPOSE: The aim is to investigate associations between mortality and exposure to ionizing radiation in a cohort of uranium workers with potential for internal and external radiation exposures. METHODS: Workers employed for at least 6 months between 1958 and 2006 in five plants involved in the French nuclear fuel cycle were included and followed up between 1968 and 2013. Cause-specific standardized mortality ratios were calculated. Analyses of associations between individual cumulative radiation dose (both internal and external, lagged by 5-15 years) and mortality were conducted using Poisson regression. RESULTS: The cohort includes 4541 workers. The mean cumulative external dose was 11.12 mGy. Mean cumulative internal doses ranged, depending on modelling hypotheses, from 0.05 to 0.09 mGy (liver) and from 4.22 to 10.90 mGy (lung). At the end of the follow-up, 838 workers were deceased and 28 lost to follow-up. A healthy worker effect was observed. The risk of prostate and lung cancers mortality was significantly higher for workers exposed to cumulative external dose above 50 mGy compared to non-exposed, but these associations were based only on three cases and became non-significant, although of similar magnitude, after adjustment for smoking. Associations with internal dose showed no consistent pattern. CONCLUSIONS: For the first time, a study was conducted in a French cohort of uranium workers with a complete reconstruction of internal dose. Results are preliminary and must be interpreted with caution because of the limited cohort size and significant sources of uncertainty. Future steps of this study will overcome these limitations.

INITIAL EVALUATION OF INDIVIDUAL DOSES IN THE EARLY PHASE OF A NUCLEAR REACTOR ACCIDENT BASED ON IN-VIVO MONITORING DATA AND SIMULATED RADIOLOGICAL CONSEQUENCES.

In the early phase of a nuclear reactor accident, in-vivo monitoring of impacted population would be highly useful to detect potential contamination during the passage of the cloud and to estimate the dose from inhalation of measured radionuclides. However, it would be important to take into account other exposure components: (1) inhalation of unmeasured radionuclides and (2) external irradiation from the plume and from the radionuclides deposited on the soil. This article presents a methodology to calculate coefficients used to convert in-vivo measurement results directly into doses, not only from the measured radionuclides but from all sources of exposure according to model-based projected doses. This early interpretation of in-vivo measurements will provide an initial indication of individual exposure levels. As an illustration, the methodology is applied to two scenarios of accidents affecting a nuclear power plant: a loss-of-coolant accident leading to core meltdown and a steam generator tube rupture accident.

Risk of Lung Cancer Mortality in Nuclear Workers from Internal Exposure to Alpha Particle-emitting Radionuclides.

BACKGROUND: Carcinogenic risks of internal exposures to alpha-emitters (except radon) are poorly understood. Since exposure to alpha particles-particularly through inhalation-occurs in a range of settings, understanding consequent risks is a public health priority. We aimed to quantify dose-response relationships between lung dose from alpha-emitters and lung cancer in nuclear workers. METHODS: We conducted a case-control study, nested within Belgian, French, and UK cohorts of uranium and plutonium workers. Cases were workers who died from lung cancer; one to three controls were matched to each. Lung doses from alpha-emitters were assessed using bioassay data. We estimated excess odds ratio (OR) of lung cancer per gray (Gy) of lung dose. RESULTS: The study comprised 553 cases and 1,333 controls. Median positive total alpha lung dose was 2.42 mGy (mean: 8.13 mGy; maximum: 316 mGy); for plutonium the median was 1.27 mGy and for uranium 2.17 mGy. Excess OR/Gy (90% confidence interval)-adjusted for external radiation, socioeconomic status, and smoking-was 11 (2.6, 24) for total alpha dose, 50 (17, 106) for plutonium, and 5.3 (-1.9, 18) for uranium. CONCLUSIONS: We found strong evidence for associations between low doses from alpha-emitters and lung cancer risk. The excess OR/Gy was greater for plutonium than uranium, though confidence intervals overlap. Risk estimates were similar to those estimated previously in plutonium workers, and in uranium miners exposed to radon and its progeny. Expressed as risk/equivalent dose in sieverts (Sv), our estimates are somewhat larger than but consistent with those for atomic bomb survivors.See video abstract at, http://links.lww.com/EDE/B232.

Reconstruction of Internal Doses for the Alpha-Risk Case-Control Study of Lung Cancer and Leukaemia Among European Nuclear Workers.

The Alpha-Risk study required the reconstruction of doses to lung and red bone marrow for lung cancer and leukaemia cases and their matched controls from cohorts of nuclear workers in the UK, France and Belgium. The dosimetrists and epidemiologists agreed requirements regarding the bioassay data, biokinetic and dosimetric models and dose assessment software to be used and doses to be reported. The best values to use for uncertainties on the monitoring data, setting of exposure regimes and characteristics of the exposure material, including lung solubility, were the responsibility of the dosimetrist responsible for each cohort. Among 1721 subjects, the median absorbed dose to the lung from alpha radiations was 2.1 mGy, with a maximum dose of 316 mGy. The lung doses calculated reflect the higher levels of exposure seen among workers in the early years of the nuclear industry compared to today.

Concerted Uranium Research in Europe (CURE): toward a collaborative project integrating dosimetry, epidemiology and radiobiology to study the effects of occupational uranium exposure.

The potential health impacts of chronic exposures to uranium, as they occur in occupational settings, are not well characterized. Most epidemiological studies have been limited by small sample sizes, and a lack of harmonization of methods used to quantify radiation doses resulting from uranium exposure. Experimental studies have shown that uranium has biological effects, but their implications for human health are not clear. New studies that would combine the strengths of large, well-designed epidemiological datasets with those of state-of-the-art biological methods would help improve the characterization of the biological and health effects of occupational uranium exposure. The aim of the European Commission concerted action CURE (Concerted Uranium Research in Europe) was to develop protocols for such a future collaborative research project, in which dosimetry, epidemiology and biology would be integrated to better characterize the effects of occupational uranium exposure. These protocols were developed from existing European cohorts of workers exposed to uranium together with expertise in epidemiology, biology and dosimetry of CURE partner institutions. The preparatory work of CURE should allow a large scale collaborative project to be launched, in order to better characterize the effects of uranium exposure and more generally of alpha particles and low doses of ionizing radiation.