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OCR for page 8
2
Other Studies of Radiation Exposure of
Military Personnel
INTRODUCTION
The purpose of this chapter is to provide some context for later discussion
of results in particular, to discuss whether the findings of our study are con-
sistent with what is known about the effects of radiation exposure. However,
because radiation exposure data have not been used in this report (see Chapter
7), and because our discussion of the effects of radiation exposure is necessarily
indirect, we do not provide an extensive discussion of dose-related radiation
effects in this chapter. Furthermore, there are several excellent, recent references
on radiation risk which the interested reader may consult (ICRP, 1991; National
Research Council, 1990; UNSCEAR, 1994~. We do discuss in some detail the
results of four previous mortality studies of military veterans involved in nuclear
weapons tests because the types of exposures to which they may have been
subjected (both radiation and nonradiation exposures) are more likely to be
similar to those experienced by the five-series cohort than those of nonmilitary
cohorts.
Among the studies of nonmilitary cohorts, the study of the survivor experi-
ence following the atomic bomb exposures in Hiroshima and Nagasaki the Life
Span Study (LSS:is of great importance despite the unique circumstances sur-
rounding these exposures; most radiation protection recommendations are based
primarily on LSS risk estimates (Ron et al., 1994~. The interested reader is referred
to an extensive literature on cancer incidence rates and cancer mortality rates
(fairly recent examples include Land, 1995; Mabuchi et al., 1994; Nagataki et al.,
1994; Pierce et al., 1996; Preston et al., 1994; Ron et al., 1994; Thompson et al.,
1994~; Schull (1995) provided a good overview ofthe entire LSS program.
Other studies of nonmilitary populations exposed to relatively high levels of
radiation include the following: the Andylosing Spondylitis Treatment Study
(Derby et al., 19874; the Cervical Cancer Treatment Study (Boice et al., 1988~; the
Canadian Fluoroscopy Study (Sherman et al., 1978~; the New York State Post
8
OCR for page 9
OTHER STUDIES OF RADIA TION EXPOSURE OF MILITARY PERSONNEL 9
parturn Mastitis Study (Shore et al., 1986~; and the Massachusetts Fluoroscopy
Study (Boice et al., 1978, 1981~. The results of such studies are typically extrapo-
lated mathematically to provide estimates of health effects at relatively low doses.
While studies of relatively low-dose exposures can provide a basis for en-
suring that radiation risk estimates based on higher doses neither underestimate
nor overestimate the effects of lower doses, they have their unique problems.
Chief among these are low statistical power (leading to lack of precision in risk
estimates) and the strong potential for confounding that is present in studies that
attempt to produce estimates of low relative risks. Studies of relatively low-level
radiation exposure in nonmilitary populations include studies of exposures due
to diagnostic radiology; fallout from nuclear weapons testing (populations of
residents downwind from test sites); occupational exposures; and natural back-
ground radiation. The results of these kinds of studies have been reviewed in
detail elsewhere (Boice, 1996; Boice, et al., 1996; NRC, 1990; and Ron, 1998~.
MILITARY POPULATIONS
Several epidemiologic studies of military personnel possibly exposed to
radiation during atmospheric nuclear weapons testing have contributed to the
scientific debate regarding the adverse effects of radiation exposure on human
health. These studies have reported modest elevations in risk for all-cause, all-
cancer, and leukemia mortality in participants relative to comparison groups, but
these elevations have not consistently reached statistical significance. Table 2-1
displays findings from several of the larger, controlled studies of military per-
sonnel who participated in nuclear weapons testing.
Watanabe and colleagues (1995) compared the mortality experiences of
some 8,550 military participants at Operation Hardtack I, a 1958 U.S. test series
in the Pacific Proving Ground, with a comparison group of roughly 14,600
military personnel. All-cause mortality (crude death rate ratio ERR] 1.10; 95%
confidence interval [CI] 1.02-1.19) and digestive cancer mortality (RR 1.47; CI
1.06-2.04) were higher among participants than comparisons. Mortality rates
due to all cancers, leukemia, and other suspected radiogenic cancers were not
significantly elevated among participants. When stratified by gamma radiation
doses the advisability of which the advisory committee of this report questions
(see Appendix A)- participants in the highest dose group (>1,000 millirem
fmrem]) had significant increases in mortality for all causes (RR 1.23; CI 1.04-
1.45), all cancers (RR 1.42; CI 1.03-1.96), and liver cancer (RR 6.42; CI 1.17-
35.33~. Participants in the middle dose group (250-1,000 mrem) did not demon-
strate increased mortality rates for any conditions. Participants in the low-dose
level (0-250 mrem) had significantly increased mortality rates due to digestive
organ cancer. Among the digestive organs, esophageal cancer mortality showed
the largest elevation in risk (RR 2.15), although neither it nor any other indi-
vidually classified digestive organ reached statistical significance.
OCR for page 10
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OCR for page 12
12
~, O
THE FIVE SERIES STUDY
Darby and colleagues (1993a,b) studied mortality and cancer incidence in
some 21,000 military participants (and 22,000 comparison subjects) in nuclear
weapons tests conducted by the United Kingdom in Australia and the Pacific
during the 1950s and 1960s. The study included data on deaths occurring
through 1990, extending the follow-up period reported in their earlier study an
additional 7 years (Derby et al., 1988a,b). Test participants had significantly
increased leukemia mortality during the entire follow-up period (RR 1.75; CI
1.01-3.06), with a stronger effect observed for the period 2-25 years after expo-
sure (RR 3.38; CI 1.45-8.25) than for the entire follow-up period. The investi-
gators suggested that this elevation may be due to the low rates of leukemia seen
in the comparison group during both follow-up periods, but did not rule out the
possibility that exposure to radiation from nuclear tests may have had an effect
on the leukemia risk, particularly during the earlier post-exposure period.
Pearce and colleagues (1996, 1997) investigated mortality and cancer inci-
dence (through 1992) among 528 New Zealand participants (and 1,504 compari-
son subjects) in United Kingdom nuclear weapons tests conducted in the Pacific
in 1957 and 1958. Leukemia (RR 5.59; CI 1.04 41.7) and the total hematologic
cancer group (RR 3.75; CI 1.36-10.8) mortality rates were statistically signifi-
cantly elevated. All-cause and all-cancer mortality were slightly elevated, but
did not reach statistical significance.
Johnson and colleagues (1996) at the Medical Follow-up Agency of the
Institute of Medicine investigated the mortality experience of more than 38,000
U.S. Navy personnel who participated in Operation Crossroads, a 1946 atmos-
pheric nuclear test series that took place at the Bikini Atoll in the Pacific, and
roughly 35,000 comparison personnel. The mortality experience of participants
was evaluated relative to that of a comparison group, selected to be similar to
the participants in several key ways such as branch of service, time and loca-
tion of service, age, and paygrade but who had not participated in the Cross-
roads nuclear test series. Analysis found a slight but statistically significant in-
creased risk of all-cause mortality among participants (RR 1.05; CI 1.02-1.07~.
Neither leukemia (RR 1.02; CI 0.75-1.39) nor all-cancer (RR 1.01; CI 0.9
1.07) mortality were significantly elevated among Navy Crossroads participants.
In summary, the four studies of military personnel participating in atmos-
pheric tests conducted by New Zealand, the United Kingdom, and the United
States report rather consistent findings. For all-cause mortality, rate ratios from all
four studies were slightly elevated (above 1.0~. Two of those studies showed sta-
tistically significant estimated increased risk to participants. For all-cancer mortal-
ity, three studies reported elevated mortality rates and one study showed a de-
creased rate; none of these rates was statistically different from 1.0. Three studies
reported elevated estimated risk of leukemia mortality among participants, relative
to comparisons; two of these were statistically significant. Based largely on the
findings from these studies of low-level radiation exposure in military populations,
but also based on what is generally known about radiation effects, our study has
focused on all-cause, all-cancer, and leukemia mortality as primary endpoints (see
Chapter 9~.
Representative terms from entire chapter:
radiation exposure
