Health Risks of Ionizing Radiation: - Clark University

114 Radiation Exposure in Flight
fact that AML incidence apparently increased with
the duration of employment 2 . An American study
of pilots found elevated prostate cancer mortality
and significantly increased mortality from cancer
of the kidney or renal pelvis. This study showed
equivocal leukemia results (16 observed cases and
~15 expected) but did not separate leukemia cases
by type (Nicholas et al 1998).
The rest of the studies that we looked at were
conducted in northern Europe and compared cancer
rates in flight crew to national rates. All but one
of these studies found significantly increased skin
cancer incidence, and one found a significant skin
cancer trend with dose (Pukkala et al 2002) 3 . A
study of Danish pilots found a three-fold increase
in AML but the result was not significant (4 cases,
1.4 expected cases). When dividing the cohort by
type of aircraft flown, however, jet pilots (who
fly at higher altitudes) were observed to have a
significantly increased risk of AML 4 (Gundestrap
and Storm 1999). A study of Norwegian flight
attendants found significantly increased incidence of
cancer of the skin, liver, upper respiratory tract, and
gastric tract in men, and of skin cancer in women.
Total cancer rates were also increased (Haldorsen et
al 2001). A study of German flight attendants found
no significant mortality differences with the general
population (Blettner et al 2002) but did not analyze
cancer incidence.
Each of these studies alone is somewhat limited
by small numbers and so it is useful to attempt a
meta-analysis that pools multiple study results.
Elsebeth Lynge from the University of Copenhagen
did this in 2001: among male pilots there were
increases in three types of cancer- prostate cancer
(SIR 1.3), skin cancer (SIR 2.0) and AML (SIR 3.8,
1.9-6.7). Among female flight attendants there was
evidence of increased breast cancer risk (SIR 1.4)
and among men there was evidence of increased
liver and upper respiratory tract cancer (perhaps due
to drinking). Flight attendants also showed weak
evidence of increased total leukemia risk in addition
to a clear increase in skin cancer incidence.
The most consistent finding in these studies was
increased skin cancer and it is not clear that this is
linked to radiation. The Danish study found similar
skin cancer results in high- and low-altitude pilots,
evidence against a radiation cause. One author has
suggested that flying over multiple time zones might
contribute to skin cancer (melanoma) by disrupting
circadian rhythms and thus the homeostasis of
melatonin (Raffnson et al 2000), and various authors
have proposed that lifestyle factors unique to flight
crew (excessive sunbathing) might be involved or
that increased detection plays a role. On the other
hand the largest study found a significant skin cancer
trend with dose (Pukkala et al 2002).
9.2 Cell studies
Several studies have looked for cell-level
abnormalities in pilots and other flight crew with
mixed results. Two studies by an Italian research
team looked for chromosome abnormalities and
DNA damage. These authors found increased
‘stable’ chromosome abnormalities (translocations,
gaps and breaks), nonsignificant elevations of
‘unstable’ abnormalities (micronuclei, dicentrics,
fragments and rings), and a nonsignificant increase
in DNA single or double strand breaks (RR 1.36;
0.46, 3.98). In another Italian study Romano et al.
(1997) found roughly twice as many dicentric and
ring chromosomes in Italian flight personnel as in
controls. Heimers (2000) found increased numbers
of dicentric chromosomes (~8-fold increase) and
translocations (~4-fold increase) in British Concorde
pilots exposed to 3-6 mSv/yr. Nicholas et al. (2003)
found a roughly threefold increase in translocations
among pilots. In a study of Dutch flight engineers
two types of effects were studied- DNA damage and
DNA protection and repair. Flight engineers were
shown to have significantly higher rates of oxidative
2 For two cases with less than 20 years of employment the SIR was 3.8 (90% CI 0.7, 11.9); for four cases with over
twenty years of employment the SIR was 5.4 (90% CI 1.8, 12.4)
3 Compared to pilots with less than 3 mSv of cumulative dose, pilots with more than 20 mSv were almost three times
more likely to develop melanoma (RR 2.78; 1.30, 5.93).
4 Among all jet pilots 3 cases of AML were observed versus 0.65 expected (SIR 4.6; 0.9, 13.4). All of these cases were
in pilots with more than 5000 flight hours, bringing the SIR for that group to 5.1. Among non-jet pilots there was 1
case of AML (0.75 expected).