Documents Richardson, David 6 results

"The U.S. government recently implemented rules for awarding compensation to individuals with cancer who were exposed to ionizing radiation while working in the nuclear weapons complex. Under these rules, chronic lymphocytic leukemia (CLL) is considered to be a nonradiogenic form of cancer. In other words, workers who develop CLL automatically have their compensation claim rejected because the compensation rules hold that the risk of radiation-induced CLL is zero. In this article we review molecular, clinical, and epidemiologic evidence regarding the radiogenicity of CLL. We note that current understanding of radiation-induced tumorigenesis and the etiology of lymphatic neoplasia provides a strong mechanistic basis for expecting that ionizing radiation exposure increases CLL risk. The clinical characteristics of CLL, including prolonged latency and morbidity periods and a low case fatality rate, make it relatively difficult to evaluate associations between ionizing radiation and CLL risk via epidemiologic methods. The epidemiologic evidence of association between external exposure to ionizing radiation and CLL is weak. However, epidemiologic findings are consistent with a hypothesis of elevated CLL mortality risk after a latency and morbidity period that spans several decades. Our findings in this review suggest that there is not a persuasive basis for the conclusion that CLL is a nonradiogenic form of cancer."

"Previous studies concluded that there was no evidence that the 1979 nuclear accident at Three Mile Island( TMI) affected cancer incidence in the surrounding area; however there were logical and methodological problems in earlier reports that led us to reconsider data previously collected.
A 10-mile area around TMI was divided into 69 study tracts, which were assigned radiation dose estimates based on radiation readings and models of atmospheric dispersion. Incident cancers from 1975 to 1985 were ascertained from hospital records and assigned to study tracts.
Associations between accident doses and incidence rates of leukemia, lung cancer, and all cancer were assessed using relative dose estimates calculated by the earlier investigators. Adjustments were made for age, sex, socioeconomic characteristics and preaccident variation in incidence.
Considering a 2-year latency, the estimated percent increase per dose unit +- standard error was 0.020 * 0.012 for all cancer, 0.082 +- 0.032 for lung cancer, and 0.116 * 0.067 for leukemia.
Adjustment for socioeconomic variables increased the estimates to 0.034+- 0.013, 0.103 +- 0.035, and 0.139 ? 0.073 for all cancer, lung cancer and leukaemia, respectively. Associations were generally larger considering a 5-year latency, but were based on smaller numbers of cases, results support the hypothesis that radiation doses are related to increased cancer incidence around TMI. The analysis avoids medical detection bias, but suffers from inaccurate dose classification; therefore, results may underestimate the magnitude of the association between radiation and cancer ncidence. These associations would not be expected, based on previous estimates of near background levels of radiation exposure following the accident."

"PURPOSE:
Reported elevations of multiple myeloma among nuclear workers exposed to external penetrating ionizing radiation, based on small numbers of cases, prompted this multi-facility study of workers at US Department of Energy facilities.
METHODS: Ninety-eight multiple myeloma deaths and 391 age-matched controls were selected from the combined roster of 115,143 workers hired before 1979 at Hanford, Los Alamos National Laboratory, Oak Ridge National Laboratory, and the Savannah River site. These workers were followed for vital status through 1990 (1986 for Hanford). Demographic, work history, and occupational exposure data were derived from personnel, occupational medicine, industrial hygiene, and health physics records. Exposure-disease associations were evaluated using conditional logistic regression.
RESULTS: Cases were disproportionately African American, male, and hired prior to 1948. Lifetime cumulative whole body ionizing radiation dose was not associated with multiple myeloma, however, there was a significant effect of age at exposure, with positive associations between multiple myeloma and doses received at older ages. Dose response associations increased in magnitude with exposure age (from 40 to 50) and lag assumption (from 5 to 15 years), while a likelihood ratio goodness of fit test reached the highest value for cumulative doses received at ages above 45 with a 5-year lag (X2=5.43,1 df; relative risk = 6.9% per 10 mSv). Dose response associations persisted with adjustment for potential confounders.
CONCLUSIONS: Multiple myeloma was associated with low level whole body penetrating ionizing radiation doses at older ages. The exposure age effect is at odds with interpretations of A-bomb survivor studies but in agreement with several studies of cancer among nuclear workers."

"Large-scale epidemiological studies of U.S. Department of Energy workers have been underway since the 1960s. Despite the increasing availability of information about long-term follow-up of badge-monitored nuclear workers, standard-setting bodies continue to rely on the Life Span Study (LSS) of A-bomb survivors as the primary epidemiological basis for making judgments about hazards of low-level radiation. Additionally, faith in the internal and external validity of studies of A-bomb survivors has influenced decisions about the design, analysis, and interpretation of many worker studies. A systematic comparison of the LSS and worker studies in terms of population characteristics, types of radiation exposures, selection factors, and dosimetry errors suggests that the priority given to dose response findings from the LSS is no longer warranted. Evidence from worker studies suggests that excess radiation-related cancer deaths occur at doses below the current occupational limits; low-dose effects have also been seen in studies of childhood cancers in relation to fetal irradiation. These findings should be considered in revising current radiation protection standards. "

Methods for evaluating age related differences in epidemiologic studies examining the effects of prolonged exposures were discussed. Subcohort analyses, use of weighting functions, and evaluating separate effects of cumulative exposure received at different age ranges (cross/classification analysis) were described. Subcohort analysis is usually done by distinguishing between individuals whose exposure histories begin at different ages or by using age at first exposure and age at last exposure in the analysis. Weighting functions can be used to discount exposures received before a certain age or to discount exposures not considered to be etiologically relevant. A variety of mathematical functions including step functions or linear, quadratic, or sigmoid weighting functions can be used for this purpose. Cross classification analysis can be used to separate the effects of cumulative exposure received at two different age ranges, thereby enabling trends in disease rates with increasing exposure received at one age period to be evaluated. The approaches were illustrated by application to a followup cohort study of the risk of cancer among employees at Oak Ridge National Laboratory (ORNL). The ORNL cohort consisted of 8,307 white males who had been hired between 1943 and 1972 and worked at the facility for at least 30 days. Subcohort analysis showed that an increase in cancer mortality occurred only in workers who received higher radiation exposures at ages of 45 years (yr) or greater. Workers in this age group showed an 8.55% increase in all cancer mortality per every 10 millisieverts (mSv) radiation exposure versus only a 3.02% increase in cancer mortality per 10mSv received before age 45yr. Cross classification analysis indicated that cumulative radiation doses received after age 45 were associated with a 5.46% increase in all cancer mortality per 10mSv exposure, whereas radiation doses received before age 45 were associated with only a 0.69% increase in cancer mortality per 10mSv. The weighting function approach also indicated that cancer mortality increased with age at exposure, the percentage increase per 10mSv varying from 2.28 to 6.49% depending on which particular function was used. The authors conclude that each method can contribute to the overall evaluation of age specific exposure effects in epidemiological studies.

"Changes in the workforce during the civil rights movement may have impacted occupational exposures in the United States. We examined Savannah River Site (SRS) employee records (1951-1999) for changes in radiation doses and monitoring practices, by race and sex. Segregation of jobs by race and sex diminished but remained pronounced in recent years. Female workers were less likely than males to be monitored for occupational radiation exposure [odds of being unmonitored = 3.11; 95% CI: (2.79, 3.47)] even after controlling for job and decade of employment. Black workers were more likely than non-black workers to have a detectable radiation dose [OR = 1.36 (95% CI: 1.28, 1.43)]. Female workers have incomplete dose histories that would hinder compensation for illnesses related to occupational exposures. The persistence of job segregation and excess radiation exposures of black workers shows the need for further action to address disparities in occupational opportunities and hazardous exposures in the U. S. South."