Scenario       Cosmic rays are one of the main hazards for long-term manned space missions. Astronauts/cosmonauts are exposed to various types of high energy charged particles of the galactic or solar origin. They include electrons, positrons, protons or heavier ions of high energy. However, the cosmic ray flux around the space crafts are significantly different from those in free space since the primary cosmic rays are decelerated by and bombarding the structure of the space crafts, and hence producing a variety of secondary particles inside the space crafts. The radiation environment of the astronauts is thus considerably differs depending on space activity, e.g., missions inside the space craft or extra-vehicle activity. Heavy ion bombardment may produce one-third of the total neutron flux, and in the International Space Station (ISS; image by Wikipedia 2015), it has been estimated that approximately 30 % of the dose received by the astronauts comes from the albedo neutrons and secondary neutrons created by interactions in the shielding materials. The neutron energies should extend from thermal energies up to a few GeV. The total radiation environment is thus completely different from that we can experience, naturally or experimentally, on the earth. Moreover, the biological response is also complex, for instance, like photons, neutrons can activate DNA repair pathways (adaptive response) as well at low doses while high LET charged particles do not. The health consequences of hits by HZE particles not clear. The health effects associated with the manned space exploration in the mixed radiation field and their quantitative evaluation is the major concern in the current space radiobiology. Chromosome aberration analysis has been carried out in the cosmonauts/astronauts to meet this requirement.

References
     Testard, I., Ricoult, M., Hoffschir, F., Flury-Herard, A., Dutrillaux, B., Fedorenko, B., Gerasimenko, V. and Sabatier, L. (1996): Radiation-induced chromosome damage in astronauts’ lymphocytes. Int. J. Radiat. Biol., 70:403-411.

Chromosome aberration analysis
     Blood samples were taken from Russian (R) and French (F) astronauts 1-2 months before and 1 and 7 days after space missions ANTARES (1992) and ALTÏR (1993). Chromosomes were analyzed by R-banding or Giemsa staining method. The increase in chromosome damage, as measured by chromosome breaks, was negligible for 2 week mission (F1) and slight for 3 week mission (F2). However, significant increase of chromosome damage was found for 6 month missions (R1-R5). Cells with multiple chromosome aberrations (rogue cells) were observed in post-flight samples of R3 (one in 1000 cells) and R5 (4 in 1100 cells). The cells with 8 or more breaks were considered as “rogue” cells. The authors assumed that they could be a consequence of a hit by HZE particle and included in the damage evaluation.

Commentary (Editorial):
     As seen in the Table above, the cellular distribution of damage is given as cells with indicated number of breaks. The break distribution was converted to the approximate number of two-break aberrations by A≈int(B/2), in which A is number of two-break aberrations in a class (n-1) and B is number of breaks in a class (n). Then, the dose distribution profiles were obtained by unfolding aberration distribution of virtuailized dicentrics and rings.

Reference
     Obe, G., Johannes, I., Johannes, C., Hallman, K., Reitz, G. and Facius, R. (1997): Chromosomal aberrations in blood lymphocytes of astronauts after long-term space flights. Int. J. Radiat. Biol., 72:727-734.

Chromosome aberration analysis (conventional Giemsa method)
      Blood samples were taken from the astronauts a few days before (BF-samples) and after return from the last space flight (AF-samples). Chromosome aberrations were analyzed by conventional Giemsa staining method. Chromosome-type aberrations were significantly elevated in blood samples taken after flight as compared to those before. Two cells with multiple aberrations (rogue cells) were observed in post-flight sample of astronaut A2.

Reference
     Fedorenko, B., Druzhinin, S., Yudaeva, L., Petrov, V., Akatov, Yu., Snigiryova, G., Novitskaya, N., Shevchenko, V. and Rubanovich, A. (2001): Cytogenetic studies of blood lymphocytes from cosmonauts after long-term space flight on MIR station. Adv. Space Res., 27:355-359.

Chromosome aberration analysis
     Chromosome aberration analyses were carried out on a total of 22 cosmonauts 1-2 months before and a day after long-term space flight on MIR station. Some of the cosmonauts were examined after repeated flights. The duration of the mission was on average 4-6 months. Chromosome preparations were stained by Giemsa and chromosome-type aberrations were scored.
     In most of the cosmonauts, the chromosome aberration frequencies were significantly higher in the post-flight samples as compared to those in pre-flight samples, on average approximately 3 times elevation.

Reference
     Durante, M., Snigiryva, G., Akaeva, E., Bogomazova, A., Druzhinin, S., Fedorenko, B., Greco, O., Novitskaya, N., Rubanovich, A., Shevchenko, V., von Recklinghausen, U. and Obe, G. (2003): Chromosomal aberration dosimetry in cosmonauts after single or multiple space flight. Cytogenet. Genome Res., 103:40-46.

Chromosome aberration analysis
     Chromosome analyses were carried out in blood samples from 33 crew members of long-term missions on MIR or the International Space Station (ISS), and on short-term taxi flights, spanning about ten years (from 1992 to 2003). Chromosome aberrations were analyzed either by Giemsa staing or by FISH painting.

Reference
     Hayata, I., Koike, Y., Minamihisamatsu, M., Yabe, S., Shurshackov, V. A., Snigiryova, G. P. and Bogomazova, A. (2008): Chromosome aberrations in astronauts. In; Taniguchi, K. and Zhang, X. eds., “Advances in Chromosome Sciences”, Vol. 3., pp.110-111.

Chromosome aberration analysis
     Peripheral blood samples were obtained from 5 Russian astronauts at the Institute of BioMedical Problems (INMP), Russia. The blood was cultured at the Institute of Roentgenology and Radiology (IRR), Russia, and the fixed samples were brought to the National Institute of Radiological Sciences (NIRS), Japan. Chromosomes were studied by both conventional Giemsa staining method and FISH painting method.
     The authors concluded that the frequencies of dicentrics and rings as studied by solid Giemsa method significantly increaed in the post-flight samples, but the changes in translocation frequencies as revealed by FISH painting were not conclusive.