|A threshold dose is a dose level below
which there is no effect of radiation on the biological response.
It is often difficult to distinguish between a threshold
and a linear-quadratic
dose response where the response changes only
slightly at low doses. A threshold model postulates that
radiation does not cause the effect at any level below the
threshold. Radiation thresholds are generally thought to
be limited to acute (short-term) effects that are called deterministic,
because they require depletion of certain cells in the body
to below a critical number in a given organ or tissue. These
effects include radiation sickness (nausea and vomiting),
infection and bleeding, and loss of hair.