Biological dosimetry for astronauts: a real challenge

Manned space missions recently increased in number and duration, thus it be came important to estimate the biological risks encountered by astronauts. They are exposed to cosmic and galactic rays, a complex mixture of differen t radiations. In addition to the measurements realized by physical dosimete rs, it becomes essential to estimate real biologically effective doses and compare them to physical doses. Biological dosimetry of radiation exposures has been widely performed using cytogenetic analysis of chromosomes. This approach has been used for many years in order to estimate absorbed doses i n accidental or chronic overexposures of humans. In addition to conventiona l techniques (Giemsa or FPG staining, R- or G-banding), faster and accurate means of analysis have been developed (fluorescence in situ hybridization [FISH] painting). As results accumulate, it appears that strong interindivi dual variability exists in the basal level of aberrations. Moreover, some a berrations such as translocations exhibit a high background level. Radiatio n exposures seem to induce variability between individual responses. Its ex tent strongly differs with the mode of exposure, the doses delivered, the k ind of radiation, and the cytogenetic method used. This paper aims to revie w the factors that may influence the reliability of cytogenetic dosimetry. The emphasis is on the exposure to high linear energy transfer (LET) partic les in space as recent studies demonstrated interindividual variations in d oses estimated from aberration analysis after long-term space missions. In addition to the problem of dose estimates, the heterogeneity of cosmic radi ation raises questions relating to the real numbers of damaged cells in an individual, and potential long-term risks. Actually, densely ionizing parti cles are extremely potent to induce late chromosomal instability, and again , interindividual variability exists in the expression of damage. (C) 1999 Elsevier Science B.V. All rights reserved.