Study of coverage of confidence intervals for the standardized mortality ratio in studies with missing death certificates.

This paper assesses the coverage probability of commonly used confidence intervals for the standardized mortality ratio (SMR) when death certificates are missing. It also proposes alternative confidence interval approaches with coverage probabilities close to .95. In epidemiology, the SMR is an important measure of risk of disease mortality (or incidence) to compare a specific group to a reference population. The appropriate confidence interval for the SMR is crucial, especially when the SMR is close to 1.0 and the statistical significance of the risk needs to be determined. There are several ways to calculate confidence intervals, depending on a study characteristics (ie, studies with small number of deaths, studies with small counts, aggregate SMRs based on several countries or time periods, and studies with missing death certificates). This paper summarizes the most commonly used confidence intervals and newly applies several existing approaches not previously used for SMR confidence intervals. The coverage probability and length of the different confidence intervals are assessed using a simulation study and different scenarios. The performance of the confidence intervals for the lung cancer SMR and all other cancer SMR is also assessed using the dataset of French and Czech uranium miners. Finally, the most appropriate confidence intervals to use under different study scenarios are recommended.

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.

Dissolution characteristics of uranium and lead in simulated lung fluid using fly ash samples from coal-fired power plants in the Czech Republic.

Samples of fly ash, slag and boiler scale containing elevated amounts of uranium or lead (210Pb) from several coal-fired power stations in the Czech Republic were collected for an assessment of their dissolution parameters - the dissolution rates and their respective fractions in vitro. The dissolution data were fitted either by a biexponential model or by a triexponential model. The uranium 234U and 238U in the fly ash sample are classified as M-type. Similarly, type M could be attributed for most of the materials containing 210Pb. A complementary measurement of the activity concentrations of 210Pb in relation to the grain size confirmed that the radionuclide is deposited mainly in fine particles (<25 µm).

DETERMINATION OF TOLERANCE LEVELS IN RADIOTHERAPY DOSIMETRY BASED ON STATISTICAL INTERFERENCE.

The most important dosimetry quantity that is determined at radiotherapy centers is the absorbed dose to water for external beams. Fixed tolerances for absorbed doses measured under reference conditions with an ionization chamber for high-energy photon and electron beams are usually 2 and 3%, respectively, regardless of uncertainties of the input variables and other conditions during evaluation. In reality, this agreement should be evaluated considering the uncertainties of the input variables because they affect the size of the random deviations of the measurements from their true values. The aim of this work was to develop a new approach to evaluate the agreement between measured and reported values based on statistical interference rather than to use fixed tolerance levels. The proposed method considers different scenarios that can occur during the evaluation of agreement. Because the method is described in general, it can be used in all similar situations when partial uncertainties can be established.

ASSOCIATION OF 210Po CONTENT IN URINE WITH CONCENTRATION OF 222Rn IN DWELLINGS.

Effect of indoor radon concentrations higher than 500 Bq m-3 in dwellings on excretion of 210Po was studied in 28 volunteers. The study was further augmented by following eight individuals from the group for 5 months at 1-month intervals. Association between 222Rn concentration in homes and 210Po excretion was found when the dataset containing values of the studied 27 subjects was combined with data on 40 Prague inhabitants from the previous study. Sources of uncertainties involved in the analysis are discussed.

238U CONTENT IN URINE OF URANIUM MINERS AND ITS MODELED VALUES.

The aim of the study is to make a comparison of daily 238U excretion in urine among 115 active uranium miners and its modeled values obtained from inhalation intake of long-lived alpha emitters as measured by personal dosemeters and assessed by biokinetic models for different absorption parameters settings for inhaled uranium. A total of 144 spot samples of urine were collected. The 238U content was measured using high-resolution inductively coupled plasma mass spectrometry method. To obtain estimates of the daily excreted values, the daily values were calculated according to the expected daily excretion of creatinine assessed individually for each miner. When determining the relation between the experimentally found data and the modeled data, a high emphasis was placed on uncertainty of the both compared quantities. All the tested absorption parameters settings produced in average 1.4-4.7-fold higher values than the experimentally found values in the urine.

Urinary excretion of uranium in adult inhabitants of the Czech Republic.

The main aim of this study was to determine and evaluate urinary excretion of uranium in the general public of the Czech Republic. This value should serve as a baseline for distinguishing possible increase in uranium content in population living near legacy sites of mining and processing uranium ores and also to help to distinguish the proportion of the uranium content in urine among uranium miners resulting from inhaled dust. The geometric mean of the uranium concentration in urine of 74 inhabitants of the Czech Republic was 0.091 mBq/L (7.4 ng/L) with the 95% confidence interval 0.071-0.12 mBq/L (5.7-9.6 ng/L) respectively. The geometric mean of the daily excretion was 0.15 mBq/d (12.4 ng/d) with the 95% confidence interval 0.12-0.20 mBq/d (9.5-16.1 ng/d) respectively. Despite the legacy of uranium mines and plants processing uranium ore in the Czech Republic, the levels of uranium in urine and therefore, also human body content of uranium, is similar to other countries, esp. Germany, Slovenia and USA. Significant difference in the daily urinary excretion of uranium was found between individuals using public supply and private water wells as a source of drinking water. Age dependence of daily urinary excretion of uranium was not found. Mean values and their range are comparable to other countries, esp. Germany, Slovenia and USA.