Radiobiology > Biologic Interactions > Cel Survival Curve > The Shoulder and Sublethal Damage

The Shoulder of the Curve: Sub-lethal Damage (SLD)

The cell survival curves for low LET radiations generally have an early, gently-sloping portion known as the shoulder.  Recall that slope of a cell survival curve represents colony survival for a given dose of radiation.

The shoulder is the region where cells conduct repair of damage and are capable of surviving. Recall that the quasi-threshold dose, Dq, represents the sub-lethal dose.

Such repair generally requires about 6 hours, but the capacity for repair can vary markedly between cell classes.

• Example of SMALL capacity for repair of SLD: Lymphocytes
• Example of LARGE capacity for repair of SLD: Jejunal crypt stem cells

Manipulation of the post irradiation environment can also lead to enhanced survival. Thus, damage may be potentially lethal, yet under supportive conditions cells survival may increase by a factor of 4-10.