PubMed Health⌕ Search

Biomedical subjects

J J Fix

Publications and source records attributed to J J Fix.

4 recordsLinked to original sources
PubMed2006

External dose estimation for nuclear worker studies.

Epidemiological studies of nuclear workers are an important source of direct information on the health effects of exposure to radiation at low doses and low dose rates. These studies have the important advantage of doses that have been measured objectively through the use of personal dosimeters. However, to make valid comparisons of worker-based estimates with those obtained from data on A-bomb survivors or persons exposed for medical reasons, attention must be given to potential biases and uncertainties in dose estimates. This paper discusses sources of error in worker dose estimates and describes efforts that have been made to quantify these errors. Of particular importance is the extensive study of errors in dosimetry that was conducted as part of a large collaborative study of nuclear workers in 15 countries being coordinated by the International Agency for Research on Cancer. The study, which focused on workers whose dose was primarily from penetrating gamma radiation in the range 100 keV to 3 MeV, included (1) obtaining information on dosimetry practices and radiation characteristics through the use of questionnaires; (2) two detailed studies of exposure conditions, one of nuclear power plants and the other of mixed activity facilities; and (3) a study of dosimeter response characteristics that included laboratory testing of 10 dosimeter designs commonly used historically. Based on these efforts, facility- and calendar year-specific adjustment factors have been developed, which will allow risks to be expressed as functions of organ doses with reasonable confidence.

Artifacts↗
PubMed1996

An approach to evaluating bias and uncertainty in estimates of external dose obtained from personal dosimeters.

This paper describes an approach to quantifying errors in recorded estimates of external radiation dose obtained from personal dosimeters and applies the approach to dose estimates of workers at the Hanford site. Because a major objective of this evaluation is to provide the information needed for adjusting epidemiologic dose-response analyses of worker data for errors in dose estimates, the paper addresses the extent that errors for different workers are correlated, focuses on recorded doses as estimates of organ doses, and focuses on recorded doses as estimates of organ doses, and gives consideration to both annual and cumulative doses. The evaluation emphasizes errors resulting from the fact that dosimeters are limited in their ability to respond accurately to all radiation energies to which workers are exposed or to radiation coming from all directions. For each of several sources of error, systematic bias factors are estimated for two energy ranges (100--300 keV and 300--1,000 keV), two geometries (anterior-posterior and rotational), and four calendar year periods. These are then combined using information provided by health physicists on energies and geometries in Hanford exposure environments. Except for the period before 1958, deep dose, the objective of modern dosimetry systems, was found to be fairly accurately estimated. Lung dose was found to be overestimated by about 10%, and bone marrow dose was found to be overestimated by about 50%. However, many aspects of this evaluation relied heavily on subjective judgments, and, thus, these factors are subject to considerable uncertainty. Estimates of uncertainty in the bias factors and uncertainty reflecting random error are provided.

Bias↗
PubMed1995

Accounting for bias in dose estimates in analyses of data from nuclear worker mortality studies.

Although dose estimates used in epidemiologic studies of nuclear workers are far superior to exposure measures used in many epidemiologic studies, they are subject to several types of bias. These include bias resulting from practices used to measure and record very low doses and from underestimation of dose from neutrons. They also include bias resulting because available dose estimates do not include dose from internally deposited radionuclides, occupational dose received after workers have terminated employment at the facility of interest, or dose from background or medical exposures. These biases can potentially distort dose-response analyses and lead to biased risk estimates and confidence limits. This paper uses data on workers at the Hanford site to investigate the possible effects of these biases on dose-response analyses of leukemia and of all cancer except leukemia. This is accomplished by conducting analyses based on a variety of assumptions regarding the nature and magnitude of these biases. Results were not modified greatly (as compared to those based on the dose as recorded) for any of the 40 sensitivity analyses presented, including some based on fairly extreme assumptions. However, analyses that excluded workers with potential for dose from internal depositions and from neutrons did increase both the risk estimate and upper confidence limits; it may be desirable to emphasize this approach in future presentations. It is recommended that similar sensitivity analyses be performed with data from other worker studies, addressing the specific dosimetry problems that have been identified in those populations.

Bias↗