Differences in repair in heterogeneous cell populations in vivo and in vitro following high LET irradiation (neutrons).

The shape of cell survival curves following X-irradiation when the X-rays were given immediately after neutron irradiation has been examined in two cell lines in vitro (Ehrlich ascites and V79) and in the stem cells of the mouse jejunum. The changes in the shape of the X-ray survival curve following neutron irradiation are different in all the cell systems examined. Some of the changes observed may be associated with a change in the cell profile following neutron irradiation due to the more even cell age killing pattern of neutrons through the cell cycle compared with X-rays. It is unlikely that this can account for all changes in shape observed and it is postulated that some cells following neutron irradiation are more sensitive to X-rays than the unirradiated population or than X-irradiated cells at the same level of survival. This increased sensitivity may be associated with a non-reversible sublethal damage or a saturation of the repair potential caused largely by the alpha or heavy recoil (HR) particles produced by the neutrons in the cell nucleus. The damage is observed when the probability of alpha or HR particles being produced within the cell nucleus, without killing the cell, is high.