Abstract

Background: Translocations, the most stable form of chromosome aberrations, are an established biomarker of cumulative exposure to external ionizing radiation. Airline pilots are exposed to varying levels of cosmic ionizing radiation, but to date, there have been few flight crew studies that have examined translocations in relation to flight experience.

Methods: We determined the frequency of translocations in the peripheral blood lymphocytes of 83 airline pilots and 50 comparison subjects (mean age = 47 and 46 years, respectively). Translocations were scored in an average of 1039 cell equivalents (CE) per subject using fluorescence in situ hybridization (FISH) whole chromosome painting and expressed per 100 CE. Negative binomial regression models were used to assess the relationship between translocation frequency and exposure status and flight years, adjusting for age, self-reported personal diagnostic x-ray procedures, and military flying.

Results: There was no significant difference in the adjusted mean translocation frequency of pilots and the comparison group (0.37 ± 0.04 vs. 0.38 ± 0.06 translocations/100 CE, respectively). However, among the pilots, the adjusted translocation frequency was significantly associated with flight years (P = 0.01) with rate ratios of 1.06 (95% CI 1.01 to 1.11) and 1.81 (95% CI 1.16 to 2.82) for a 1- and 10-year incremental increase in flight years, respectively. The adjusted rate ratio for pilots in the highest compared to those in the lowest quartile of flight years was 2.59 (95% CI 1.26 to 5.33).

Conclusions: Our data suggest that pilots with long-term flying experience may be exposed to biologically significant doses of ionizing radiation. Epidemiologic studies with longer follow-up of larger cohorts of pilots with a wide range of radiation exposure levels are needed to clarify the relationship between cosmic radiation exposure and cancer risk.