Apoptosis and micronuclei induction in human epithelial cells exposed to energetic carbon ions in the Bragg peak region

Space radiation is a complex mixture of charged particles from solar and galactic origins. Many of these high energy charged particles can penetrate current spacecraft shielding and produce secondary particles, creating significant health hazard. Therefore, understanding the biological effects of these particles along the particle traversal is critical in optimizing new shielding designs. Here, we studied DNA damage on monolayer culture of mammary epithelial cell line irradiated by 290 MeV/nucleon carbon ions. Frequencies of apoptosis and micronuclei (MN) induction were scored across the Bragg curve at entrance radiation doses of 0.5 and 2 Gy. The results for both doses show that the peak of apoptosis yield coincides with the physical Bragg peak. However, the peak location for the MN frequency appears to be dose dependent. We argue that the presence of a higher proportion of micronuclei prior to the Bragg peak at the higher radiation dose is the consequence of “overkill” at the physical Bragg peak location. Results of the carbon exposure were compared with the data for the same cell type exposed to γ-rays.