Philippo, H., Huiskamp, R., Winter, E. A. M., Gharbaran, B. and van der Kogel, A. J. Age Dependence of the Radiosensitivity of Glial Progenitors for In Vivo Fission-Neutron and X Irradiation.

O-2A progenitor cells are the stem cells of the myelin-forming oligodendrocytes in the central nervous system. In the epithermal reactor beams used for boron neutron capture therapy (BNCT) for treatment of brain tumors, fission neutrons are a contaminating component. To estimate the radiosensitivity of the O-2A progenitors for fission neutrons, an in vivo–in vitro clonogenic assay was used. Radiosensitivity of progenitors obtained from the spinal cord of 1- or 5-day-old rats or the optic nerve of 2- or 12-week-old rats for 1 MeV fission neutrons was compared to that for 300 kVp X rays. Dose–survival curves were fitted according to the linear-quadratic model. The resulting β component was very small to negligible. Progenitor cells obtained from rats of different ages show differences in radiosensitivity, characterized by different α values. RBE values for fission neutrons were 3.5 for 1-day-old spinal cord, 3.2 for 5-day-old spinal cord, 3.0 for 2-week-old optic nerve, and 4.3 for 12-week-old optic nerve. These high RBE values indicate the importance of minimizing the fast-neutron component in the epithermal neutron beams used for BNCT.