Dose-response and cell survival curves

Four curve shapes

A dose-response curve plots a biologic effect against dose, and the registry expects you to match each shape to its effects. Linear no-threshold (LNT): a straight line from zero, so any dose carries some risk and doubling the dose doubles the risk. LNT is the conservative model behind radiation protection standards and ALARA. Linear-quadratic no-threshold: the line curves upward, rising slowly at low doses and faster at high doses. The BEIR committee uses it for low-LET radiation such as x-rays, especially for leukemia. Linear threshold: no response until a set dose, then a straight-line rise; it is the least used. Nonlinear threshold, also called sigmoid or S-shaped: nothing below the threshold, a steep rise, then a plateau where nearly everyone is affected. It fits deterministic effects (tissue reactions) such as skin erythema, epilation, cataracts and blood count depression.