Epidemiology of Multiple Myeloma at Four DOE Sites

[Susan Gawarecki <loc@icx.net>]

Some information on radiation-related health effects I thought might be
of interest to the list.

--Susan Gawarecki

Epidemiology of Multiple Myeloma at Four DOE Sites 
Department of Epidemiology 
University of North Carolina at Chapel Hill 

An epidemiological study of multiple myeloma among Department of Energy
(DOE) workers. Multiple myeloma is a cancer of the blood-forming
tissues, affects primarily older people, and is often fatal. The study,
which began in October
of 1993, consisted of a feasibility phase, a protocol development phase,
and an implementation phase. The final report was submitted to the
funding agency, the National Institute for Occupational Safety and
Health (NIOSH), in March of
1997. 

Ionizing radiation is an accepted cause of multiple myeloma and most
other types of cancer. This study was requested by NIOSH because of
previous reports of associations of multiple myeloma with radiation
exposures of workers at the
Hanford site. The new study was intended to include more cases of the
disease, better evaluation of radiation doses, and measurement of other
occupational exposures not available in the Hanford studies. 

Facilities were chosen for inclusion in the study based on their age,
size, type of operations, and availability of basic records assembled
for past epidemiological studies. Those records included employee
rosters and information on causes
of death. These data formed the basis for choosing cases - workers who
died with multiple myeloma - and a random sample of controls who lived
to be as old as the cases. Because multiple myeloma is rare, four
facilities were chosen in
order to identify a sufficient number of cases for statistical analysis. 

We identified 98 multiple myeloma deaths and 391 age-matched controls
from a combined roster of 115,143 workers hired before 1979 at Hanford,
Los Alamos National Laboratory, Oak Ridge National Laboratory, and the
Savannah
River site, and followed for vital status through 1990 (1986 for
Hanford). Information on prior work history, smoking, medical x-rays,
and exposure to physical and chemical agents was derived from personnel,
medical, industrial hygiene and health physics records. 

The study compared exposure histories of cases and controls to
investigate whether certain occupational exposures were relatively more
common among cases. Results of these comparisons were expressed in terms
an epidemiological measure
called the odds ratio. The odds ratio is an estimate of the ratio of the
disease rate among workers with a particular characteristic compared to
those without the characteristic. An odds ratio of 1.0 indicates that
disease occurrence is the
same among people with and without the characteristic; an odds ratio of
2.0 would indicate that people with the characteristic have twice the
rate of disease as those without. We also calculated a measure of the
precision of the odds
ratios called the 95% confidence limit (95% CI). This statistic is an
indication of the stability of the odds ratio. 

We attempted to determine whether workers had been exposed to a variety
of chemical and physical agents that might be causes of multiple
myeloma, including solvents, metals, welding fumes, asbestos, ionizing
and non-ionizing radiation. With
the exception of external penetrating radiation, for which most longer
term workers had at least some badge data, information on exposures to
specific chemical and physical agents was not sufficient to assign a
quantitative exposure
estimate or even to determine with a high degree of certainty whether or
not a worker was exposed. We calculated odds ratios for many factors
although we believe that the results are not very interpretable due to
the poor measurement of
exposures. With the exception of the estimated whole body dose from
ionizing radiation, other factors were not clearly in excess among cases
compared to controls. 

External penetrating ionizing radiation was measured by individual
dosimeters. Whole body radiation dose was constructed by adding annual
external radiation doses and estimates of doses from tritium. Although
tritium is an internal
radiation exposure, it was routinely counted with external dose because
it irradiates the body uniformly. Neutron doses were included using
quality factors employed at the facilities, which varied from 8 to 20.
Tritium and neutrons comprised only a small fraction of whole body dose
estimates. 

Total cumulative radiation doses were similar between cases and
controls. However, doses received at ages 45 and above were associated
with an average 7% per 10 mSv (one rem) increased risk of multiple
myeloma, adjusted for age, race, sex, facility, period of hire, birth
cohort, monitoring for internal radionuclide contamination, and external
radiation received prior to age 45. The 95% confidence limit for this
estimate was 1-13%. For exposure at ages 45 and above, the
odds ratio for workers with cumulative doses of 50 mSv (5 rem) or
greater compared to workers with cumulative doses of less than 10 mSv
was 4.34 (95% CI 1.46-12.90). 

The association of multiple myeloma with radiation doses at older ages
is consistent with findings from some epidemiological studies of cancer
among workers and theoretical expectations that older people are more
sensitive to a
variety of carcinogens. These findings and other studies of nuclear
workers have implications for radiation protection standards for workers
and the general public. 

For a copy of the final report of this study write to:
Health-related Energy Research Branch, National Institute for
Occupational Safety and Health, Robert A. Taft Laboratories, 4676
Columbia Parkway, Mailstop R-44, Cincinnati, OH 45226-1998
-- 
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Susan L. Gawarecki, Ph.D., Executive Director
Oak Ridge Reservation Local Oversight Committee, Inc.
136 S Illinois Ave, Ste 208, Oak Ridge, TN 37830
Phone (865) 483-1333; Fax (865) 482-6572; E-mail loc@icx.net 
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