Ion beams for space radiation radiobiological effect studies

Abstract

Space radiation exposures to the heavier particles found in galactic cosmic rays (GCR) present a risk in manned space travel, particularly to the central nervous system (CNS). GCR are made up of a mixture of multiple charged particles such as protons, 4He, and 56Fe heavy ions. The most harmful to the CNS are the more highly charged and energetic (HZE) particles, including 56Fe because of their significant biological effect contribution to GCR dose and high linear energy transfer. These HZE particles can result in altered cognitive function, reduced motor function and behavioural changes and long term chronic brain disease. There is currently a lack of data on the biological response to 56Fe ions. In this regard, ground based experiments could be used to infer the effects of the cosmic environment on cell survival. A mono-energetic beam of 56Fe ions was generated by the Heavy Ion Medical Accelerator Chiba, National Institute of Radiological Sciences, Chiba, Japan. Three different types of glioblastoma multiforme (GBM) cell lines were studied. Using GBM cell lines which arise from the glia cells could aid in the understanding of the effects of space radiation to the brain. Clonogenic assay was used to determine the efficacy of the radiations. Certain strains of GBM are low-dose hypersensitive and hence, the very low doses used to study space radiation here are relevant. Results show that 0.2 Gy 56Fe (500 MeV/- 200 keV/μm) ions were able to inactivate approximately 8% of T98G, 15% LN18 and 27% of U87 cells. These results may infer and demonstrate the deleterious effects of 56Fe ions on human CNS, since a significant percentage of GBM cells were killed at very low doses. The data presented may therefore be employed in assessing risk related to high LET radiation exposure, simulating the effects in space radiation.