Exposure information for this study is obtained from the
National Dosimetry Services of the Radiation Protection
Bureau of Health Canada and from a few large organiza-
tions, such as nuclear power stations, that do their own mon-
itoring. About 80 percent of the dose records in this cohort
come from the National Dosimetry Service. Detailed
descriptions of the dosimetry have been reported previously
(3, 24).
To avoid the use of complex radiation protection termi-
nology, we shall use the term “dose” as a quantitative indi-
cator of exposure to any type of ionizing radiation. For
external radiation, the dose, expressed in millisieverts
(mSv), is calculated as the amount of energy absorbed per
gram of tissue, weighted by a modifying factor designed to
take into account the relative biologic damage caused by
different types of ionizing radiation (25). Internal doses can
be converted to millisieverts and added to the external dose.
Monitoring of external gamma, beta, and x-ray exposures
occurred throughout the period from 1951 to 1988.
Monitoring of external neutron exposures occurred during
this period for nuclear power station workers, well loggers,
and workers on accelerators. Tritium exposures were deter-
mined from urinalyses and converted to millisieverts.
Workers for whom these exposures were reported include
Atomic Energy of Canada Limited workers, workers at
nuclear power stations, and tritium luminizers. There is no
regulatory requirement to report exposures to other radio-
nuclides. These exposures have not been included in this
study. However, there exists a potential for substantial doses
from some of these radionuclides, such as radioactive iodine
as 131I, used in medical procedures.
Doses from the individual workers’ various types of
exposures have been combined into “annual doses,” which
are the basis of calculations in this study.
The National Dose Registry has recorded a value of zero
for all doses below the reporting limit of their respective
dosimetry processors, which was 0.20 mSv in most cases.
This procedure could underestimate the cumulative lifetime
doses and thus overestimate the risk. Although unlikely, con-
siderable underestimation of a cumulative dose could occur if
all doses recorded as zero were actually just below the report-
ing limit. We had insufficient information to determine the
degree of underestimation that could result from this practice.
No dose records exist for exposures incurred before 1951.
Consequently, the lifetime dose of some workers could be
Exposure information for this study is obtained from theNational Dosimetry Services of the Radiation ProtectionBureau of Health Canada and from a few large organiza-tions, such as nuclear power stations, that do their own mon-itoring. About 80 percent of the dose records in this cohortcome from the National Dosimetry Service. Detaileddescriptions of the dosimetry have been reported previously(3, 24). To avoid the use of complex radiation protection termi-nology, we shall use the term “dose” as a quantitative indi-cator of exposure to any type of ionizing radiation. Forexternal radiation, the dose, expressed in millisieverts(mSv), is calculated as the amount of energy absorbed pergram of tissue, weighted by a modifying factor designed totake into account the relative biologic damage caused bydifferent types of ionizing radiation (25). Internal doses canbe converted to millisieverts and added to the external dose. Monitoring of external gamma, beta, and x-ray exposuresoccurred throughout the period from 1951 to 1988.Monitoring of external neutron exposures occurred duringthis period for nuclear power station workers, well loggers,and workers on accelerators. Tritium exposures were deter-mined from urinalyses and converted to millisieverts.Workers for whom these exposures were reported includeAtomic Energy of Canada Limited workers, workers atnuclear power stations, and tritium luminizers. There is noregulatory requirement to report exposures to other radio-nuclides. These exposures have not been included in thisstudy. However, there exists a potential for substantial dosesfrom some of these radionuclides, such as radioactive iodineas 131I, used in medical procedures. Doses from the individual workers’ various types ofexposures have been combined into “annual doses,” whichare the basis of calculations in this study. The National Dose Registry has recorded a value of zerofor all doses below the reporting limit of their respectivedosimetry processors, which was 0.20 mSv in most cases.This procedure could underestimate the cumulative lifetimedoses and thus overestimate the risk. Although unlikely, con-siderable underestimation of a cumulative dose could occur ifall doses recorded as zero were actually just below the report-ing limit. We had insufficient information to determine thedegree of underestimation that could result from this practice. No dose records exist for exposures incurred before 1951.Consequently, the lifetime dose of some workers could be
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