Abstract In Europe, several studies are currently under- way to investigate the cancer risk of pilots and cabin crew exposed to low-level ionizing radiation of cosmic origin. Although no individualized exposure measure- ments of airline personnel are available, exposure assess- ment based on job history data is feasible. However, there is a marked variability in the level of detail of these data between studies in different countries and between subcohorts in national studies raising the issue of compa- rability of exposure estimation. In this paper we investi- gate the comparability of several methods of exposure assessment in a large German cohort of pilots and cabin crew. We found that the correlation between the esti- mates obtained by the four approaches analysed, is rela- tively high, ranging from 0.85 to 0.97. The precision at- tainable in the exposure assessment is higher than in many other epidemiological studies but can be refined further with simulation studies and comparison with on- going and future on-board measurement programmes. Introduction Possible health effects of cosmic radiation have been causing concern among aircraft personnel (and frequent flyers) for some time, with radiation-induced cancer and risks to fetal development being the major issues. Attention and awareness of cosmic radiation became focused in 1991 when the International Commission on Radiation Protection (ICRP) published the recommenda- tion that natural sources of radiation should be classified as occupational exposures for aircrew [1]. In Europe, the Council Directive 96/29 EURATOM [2] lays down basic standards of radiation protection that now have to be im- plemented by the airlines. Therefore, exposure estimates are needed. Although data of cancer risk after exposure to low- dose radiation from radiobiological models and other ep- idemiological studies are available, little is known about the specific risk after exposure to cosmic radiation, mainly in the particular circumstances that are experi- enced by aircrew. In contrast to other groups of occupationally exposed persons, such as nuclear power workers, individual radi- ation measurements for aircrew cannot easily be ob- tained due to practical obstacles in dosimetry. Cosmic ra- diation consists of a large neutron component (about 50% at usual flight altitudes) that requires special dosi- metric approaches. These have currently only been im- plemented in research programmes involving the selec- tion and calibration of adequate measurement apparatus, numerous measurement flights on typical routes and ad- ditional computations to adjust for unmeasured quanti- ties [3, 4, 5]. Some reports from national boards give es- timates of the possible exposures [6, 7]. Little is known about the health effects as such and in particular about their relationship to levels of radiation received. Epidemiological studies among pilots and cab- in crew published up to 1998 have recently been re- viewed in this journal [8]. So far, no consistent picture has emerged on site-specific cancer mortality or inci- dence among these occupational groups, except for mel- anoma incidence and female breast cancer incidence [9, 10]. Recently, four European cohort studies have con- firmed the increases in melanoma incidence [11, 12, 13] and mortality [14]; the study among Danish pilots also revealed increased rates of acute myeloid leukaemia which was not observed in a recent North American PMR (proportional mortality rate) study [15]. In terms of exposure assessment, only two studies among civil aircrew have attempted to obtain individual ra- diation dose estimates [13] based on the method described in [16]. In two studies, surrogates are used, such as haul type (long or short haul aircraft) [14] or flight hours [11]. G.P. Hammer ( ✉ ) · H. Zeeb · M. Blettner University of Bielefeld, School of Public Health, Department of Epidemiology and Medical Statistics, P.O. Box 100131, 33501 Bielefeld, Germany e-mail: gael.hammer@uni-bielefeld.de Tel.: +49-521-1063838, Fax: +49-521-1066465 U. Tveten Institutt for Energitekknikk, P.O. Box 40, 2027 Kjeller, Norway Radiat Environ Biophys (2000) 39:227–231 © Springer-Verlag 2000 ORIGINAL PAPER Gaël P. Hammer · Hajo Zeeb · Ulf Tveten Maria Blettner Comparing different methods of estimating cosmic radiation exposure of airline personnel Received: 28 March 2000 / Accepted: 1 September 2000