The role of repair in radiobiology.

Apart from cancer and mutation induction, radiobiological effects on mammals are mostly attributable to cell 'death', defined as loss of proliferative capacity. Survival curves relate retention of that capacity to radiation dose, and often manifest a quasi-threshold ('shoulder'). The shoulder is attributable to an initial mechanism of repair ('Q-repair') which is gradually depleted as dose increases. Another form of repair, which is not depleted ('P-repair'), increases the dose required to deliver an average of one lethal event per cell (dose 'D0'). Neither form of repair can unambiguously be linked with repair of defects in isolated DNA. An important initial lesion may well be disruption of the complex structural relationship between the DNA, nuclear membrane and associated proteins. One form of P-repair may be restoration of that structural relationship.