Acute Radiation Syndrome - Pathophysiology

Pathophysiology

The most commonly used predictor of acute radiation symptoms is the whole-body absorbed dose. Several related quantities, such as the equivalent dose, effective dose, and committed dose, are used to gauge long-term stochastic biological effects such as cancer incidence, but they are not designed to evaluate acute radiation syndrome. To help avoid confusion between these quantities, absorbed dose is measured in units of gray (Gy) or rad, while the others are measured in sievert (Sv) or rem. 1 rad = 0.01 Gy

In most of the acute exposure scenarios that lead to radiation sickness, the bulk of the radiation is external whole-body gamma, in which case the absorbed, equivalent and effective doses are all equal. There are exceptions, such as the Therac-25 accidents and the 1958 Cecil Kelley criticality accident, where the absorbed doses in Gy or rad are the only useful quantities.

Radiotherapy treatments are typically prescribed in terms of the local absorbed dose, which might be 60 Gy or higher. Although such a dose is lethal to the local tissues (as intended), it is not lethal to the patient. The dose to the targeted tissue mass must be averaged over the entire body mass, most of which receives negligible radiation, to arrive at a whole-body absorbed dose that can be compared to the table above.