Health Risks of Ionizing Radiation: - Clark University

9
RADIATION EXPOSURE IN FLIGHT
The earth is constantly bombarded by cosmic ionizing
radiation in the form of gamma rays, neutrons and
protons, and much of this radiation is filtered out by
the atmosphere. At high altitudes the atmosphere is
a less effective filter and flight crews are therefore
exposed to more of this kind of radiation. The flightrelated
doses they receive, on the order of 1-10 mSv/
yr, fall between the current recommended maximum
exposure for the public (1 mSv/yr) and that for
radiation workers (20 mSv/yr) (ICRP 1991). One
researcher has estimated that this level of exposure
for twenty years would create a risk of fatal cancer
on the order of 1 in 1000 (Friedberg et al 1989). The
investigations into the radiological hazards of flying
have dealt with flight personnel because of the high
doses that they experience relative to passengers.
Passengers probably experience doses of 3-6 uSv per
hour of flying, depending on the route (Bottollier-
Depois et al. 2003). This is several times higher than
typical background exposure rates but still amounts
to a relatively low dose for occasional fliers. Here
we look at several epidemiological studies of cancer
rates in flight crews and also look at a few cell-level
laboratory studies using blood samples from flight
crews.
9.1 Epidemiological studies
The studies that we looked at were all based in specific
countries and focused on either cockpit crew or
cabin crew. Exposure information for these cohorts
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is limited; we know how many years each individual
worked but have only a rough sense of what the
average annual dose might be. This means that other
factors associated with flight may be contributing to
any observed risks. In addition to cosmic radiation
these cohorts are exposed to magnetic fields
generated by aircraft electrical systems and toxins
associated with fuel (such as benzene). Other factors
include disruptions in circadian rhythms when flying
through many times zones in a short period and, in the
case of pilots, a possible predisposition to colorectal
cancers associated with the sedentary nature of the
job (all of the studies that we looked at discussed
some or all of these possible confounders). Another
important consideration is the healthy worker effect-
airline pilots and crew are selected for health and
physical fitness and receive thorough routine health
evaluations. Since most of the studies discussed
below used simple incidence and mortality ratios
to compare the exposed groups to national cancer
rates this healthy worker effect was not adequately
controlled for. Under these circumstances radiationrelated
health effects are harder to detect and any
significant cancer increases should be considered
with special attention.
The earliest report that we looked at was a cohort
study of 2,740 Canadian pilots (Band et al. 1996).
Compared with the general Canadian population
these pilots showed significantly higher incidence
of myeloid leukemia (and acute myeloid leukemia
(AML) specifically) and prostate cancer 1 . Malignant
melanoma of the skin was elevated. The occupational
association with leukemia was strengthened by the
1 The pilots had significantly lower rates of mortality from both cancer and other diseases and significantly lower total
cancer incidence, indicating the healthy worker effect.