Residual DNA damage: what is left over and how does this determine cell fate?

Radiation-induced DNA damage may remain unrepaired for a number of reasons: it may be too severe, it may be in inaccessible parts of the genome, it may be induced at critical points in the cell cycle or it may be converted into large DNA deletions. This residual damage is likely to be responsible for cell death either by physical restriction of replication or transcription or by metabolic disruption due to loss of function of critical genes. Although residual damage is important, cells may differ in their ability to tolerate it, which may be a factor that determines the relative radiosensitivity of a given cell population.