A Method for Estimating Occupational Radiation Doses Subject to Minimum Detection Levels

Xue, Xiaonan; Shore, Roy E.

doi:10.1097/00004032-200301000-00005

Cited by 10 publications

(6 citation statements)

References 12 publications

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“…There is a substantial literature on errors in external radiation dose estimation due to readings below a detection or recording threshold (Gilbert and Fix, 1995;Mitchell et al, 1997;Richardson and Ciampi, 2003;Xue and Shore, 2003;Shin et al, 2005). The validity of statistical investigations of the impacts of recording practices depends, in part, upon the validity of assumptions about historical recording practices; consequently, empirical evaluations of recording practices contribute to this literature.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of external radiation dosimetry records at the Savannah River Site, 1951–1989

Richardson

Wing

Daniels

2006

J Expo Sci Environ Epidemiol

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The Savannah River Site (SRS) is one of the largest facilities in the nation's nuclear weapons complex. To date, little information has been published regarding radiation risk estimates derived from epidemiological studies of SRS workers. As part of an ongoing epidemiological cohort study of SRS workers, we have assessed the suitability of the Site's personnel radiation dosimetry information for use in epidemiological analyses. This paper provides information on historical dosimetry methods, recording practices, and the completeness of computerized dosimetry information for workers employed at SRS during the period 1951-1989, when the site was operated by the du Pont Company. The study includes 18,883 workers hired at SRS between 1951 and 1987 who were employed for at least 90 days. Documents relating to external radiation dosimetry methods were reviewed, recorded doses were examined to evaluate recording practices, and the completeness of monitoring was assessed by comparing employment history and computerized dosimetry records, and by implementing a ''nearby'' procedure for estimating values for missing annual dosimetry records. Dosimeter technology evolved over this period from two-element film dosimeters to multielement thermoluminescent dosimeters. Dosimetry measurements were recorded consistently in 0.05 millisievert (mSv) increments. Prior to 1973, recording thresholds of 0.10-0.15 mSv were used while from 1973 to 1989 a recording threshold of 0.05 mSv was used. We abstracted nearly 3 person-Sv of dosimetry information that was available in hardcopy but not in computerized format. The collective dose from the computerized and abstracted records totaled 512.1 person-Sv. A ''nearby'' method was used to estimate dose values for 13,812 employment-years for which dosimetry information was not available. The average estimated value was 0.6 mSv and the assigned collective dose derived via the ''nearby'' procedure was 8.7 person-Sv. The consistency of dosimetry practices at SRS and the completeness of historical dosimetry records are supportive of their use in epidemiologic research.

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Section: Discussionmentioning

confidence: 99%

Evaluation of external radiation dosimetry records at the Savannah River Site, 1951–1989

Richardson

Wing

Daniels

2006

J Expo Sci Environ Epidemiol

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“…Some are legitimate zero doses since office workers tended to have no occupational external radiation exposure ). Among those positive doses, it was estimated that about 98% of the weekly doses were BMDL doses, about 75% of the annual doses were censored due to BMDL (Xue and Shore 2003) and about 80% of the quarterly doses were BMDL doses. Without any adjustment of the missed doses, the average person-year cumulative dose is 4.58 mSv with an assumption of a 20-y lag.…”

Section: Application To the Ornl Studymentioning

confidence: 99%

“…The existing measurement error models mentioned above all assume the distribution of the random measurement error to be the same for all the workers and do not change with time and therefore are not applicable here. Xue and Shore (2003) and Xue et al (2004) have developed methods to estimate the true dose and the dose-response relationship when there are BMDL doses. However, their methods do not consider random measurement errors.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Health Risks Associated With Occupational Radiation Exposure: Addressing Measurement Error and Minimum Detectable Exposure Level

Xue

Kim²,

Shore

2006

Health Physics

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Occupational exposures are subject to several types of measurement errors. This paper considers two of the most common types of measurement error associated with occupational exposures: the error due to below minimum detection level and doses due to random measurement error. Doses are often recorded as zero when the exposure is below the minimum detection level. Values that are below the minimum detection level and are entered as zero lead to underestimation of the true exposure and can result in either an overestimate or underestimate of risk associated with the exposure. Random measurement error leads to an inefficient and attenuated estimate of risk associated with exposure. However, the levels of bias and inefficiency that can result from the simultaneous presence of both types of measurement error have not previously been studied. In addition, the impact of these measurement errors on the type I error and type II error for an exposure-response effect is unclear. Since the magnitude of the random error associated with cumulative exposure may vary with individuals and across time within an individual, traditional methods to correct for random measurement errors are not applicable here. Further, correcting errors for minimum detectable levels and random errors simultaneously is too complex for analytical solutions. Therefore, this paper uses simulation studies to quantitatively evaluate the magnitude of the bias, inefficiency, and type I and type II errors associated with them. The simulation results are applied to a sample of historical occupational radiation exposure data from the Oak Ridge National Laboratory. We conclude that after taking into consideration random measurement error and missed doses due to falling below the minimum detection level, radiation exposure is not significantly associated with all-cause mortality in that cohort.

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“…Except for legitimate zero doses and other special cases (for example, for workers whose film badges were not available, a plant median was used), the dose estimation method is applied to all the exposed years in order to obtain a cumulative dose of radiation for each subject. It is estimated that about 75% of the annual doses were censored due to BMDL and about 98% of the weekly doses were BMDL doses (Xue and Shore 2003). Xue and Shore (2003) have developed a Bayesian approach to estimate the dose distribution and the individual's annual doses for the ORNL study.…”

Section: Introductionmentioning

confidence: 99%

“…It is estimated that about 75% of the annual doses were censored due to BMDL and about 98% of the weekly doses were BMDL doses (Xue and Shore 2003). Xue and Shore (2003) have developed a Bayesian approach to estimate the dose distribution and the individual's annual doses for the ORNL study. This method avoids assuming a deterministic mathematical relationship between the observed doses and the true doses.…”

Section: Introductionmentioning

confidence: 99%

Estimating the Dose Response Relationship for Occupational Radiation Exposure Measured With Minimum Detection Level

Xue

Shore

et al. 2004

Health Physics

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Occupational exposures are often recorded as zero when the exposure is below the minimum detection level (BMDL). This can lead to an underestimation of the doses received by individuals and can lead to biased estimates of risk in occupational epidemiologic studies. The extent of the exposure underestimation is increased with the magnitude of the minimum detection level (MDL) and the frequency of monitoring. This paper uses multiple imputation methods to impute values for the missing doses due to BMDL. A Gibbs sampling algorithm is developed to implement the method, which is applied to two distinct scenarios: when dose information is available for each measurement (but BMDL is recorded as zero or some other arbitrary value), or when the dose information available represents the summation of a series of measurements (e.g., only yearly cumulative exposure is available but based on, say, weekly measurements). Then the average of the multiple imputed exposure realizations for each individual is used to obtain an unbiased estimate of the relative risk associated with exposure. Simulation studies are used to evaluate the performance of the estimators. As an illustration, the method is applied to a sample of historical occupational radiation exposure data from the Oak Ridge National Laboratory.

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A Method for Estimating Occupational Radiation Doses Subject to Minimum Detection Levels

Cited by 10 publications

References 12 publications

Evaluation of external radiation dosimetry records at the Savannah River Site, 1951–1989

Evaluation of external radiation dosimetry records at the Savannah River Site, 1951–1989

Estimation of Health Risks Associated With Occupational Radiation Exposure: Addressing Measurement Error and Minimum Detectable Exposure Level

Estimating the Dose Response Relationship for Occupational Radiation Exposure Measured With Minimum Detection Level

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