Evaluation of chromosome aberrations in astronaut lymphocytes after long-duration missions to the International Space Station

The Health Canada and the National Aeronautics and Space Administration biodosimetry programmes have assessed exposure of astronauts to ionizing radiation based on the frequency of chromosomal aberrations in lymphocytes after missions to the International Space Station. These assessments were performed by the analysis of chromosome aberrations in peripheral blood lymphocytes, as measured by 3-colour whole chromosome fluorescence in situ hybridization probes. A retrospective cohort of 46 astronauts with biodosimetry assessments and space missions to the ISS of at least three months were examined. The frequency of aberrations in the cultured lymphocyte samples of the astronauts were followed from shortly pre-flight to post-flight and six to eighteen months later. Dose estimates were derived from personalized calibration curves, generated from chromosome translocations quantified in pre-flight ex vivo lymphocyte samples exposed to X-ray or γ-ray doses up to 2 Gy. The frequency of translocations generally increased after the spaceflight in the lymphocytes of the astronauts. Common factors governing individual radiation response and affecting chromosomal yields are explored as possible confounders, with inter-individual differences and inter-laboratory technical variations being highlighted in the results. For five astronauts that were followed across two long-duration flights, the yield of chromosome aberration endpoints measured after the second flight were lower than expected. While stable translocations were found to be the most persistent endpoint, the combination of all chromosomal exchanges provided the most precise biological dose estimate. The relative biological effectiveness of the space radiation environment, calculated as the dose derived from calibration curves to the absorbed dose measured by crew personal dosimeters, were typically greater than X-rays. Implications of the findings in the context of the space radiation environment are discussed and comparisons are made with previous studies.