The effectiveness of cysteamine as a radioprotector against cellular damage caused by fast neutrons

Abstract

At the National Accelerator Centre (NAC) a high energy neutron beam is used routinely for particle radiotherapy. During treatment the chance of biological damage to normal tissue is cause for concern as severe late-reactions in tissue can result in debilitating effects in the patient. This study is done primarily to determine the extent to which the biological damage of a high-LET radiation source can be influenced by a chemical radioprotector. As a radioprotector mitigates biological effects by influencing the indirect action of ionizing radiation the issue of radioprotection gets more complicated when the ionization density is high. This was investigated using three types of cells, i.e. V-79 fibroblasts, CHO-KI and human lymphocytes. Micronuclei formations were used as biological endpoint. A comparative treatment of the cells to neutrons or 6°Co gamma rays was done either in the presence or absence of 25 mM cysteamine (MEA). Mixed field exposures were also applied to infer the mechanism by which MEA operates to protect cells. MEA has shown minimal toxicity to the cells but is effective in mitigating damage to cells following exposure to both photons and neutrons. However, dose modifying factors that can be calculated for neutron exposures were significantly lower than that observed for photon irradiations. No synergistic interaction was observed in mixed neutron-photon field exposures indicating that the radioprotector inhibits the induction of repairable damage.