Acute Radiation Syndrome

Acute Radiation Syndrome (ARS) (sometimes known as radiation toxicity or radiation sickness) is an acute illness caused by irradiation of the entire body (or most of the body) by a high dose of penetrating radiation in a very short period of time (usually a matter of minutes). The major cause of this syndrome is depletion of immature parenchymal stem cells in specific tissues. Examples of people who suffered from ARS are the survivors of the Hiroshima and Nagasaki atomic bombs, the firefighters that first responded after the Chernobyl Nuclear Power Plant event in 1986, and some unintentional exposures to sterilization irradiators.

The required conditions for Acute Radiation Syndrome (ARS) are:
 * The radiation dose must be large (i.e., greater than 0.7 Gray (Gy)1, 2 or 70 rads).
 * Mild symptoms may be observed with doses as low as 0.3 Gy or 30 rads.
 * The dose usually must be external ( i.e., the source of radiation is outside of the patient’s body).
 * Radioactive materials deposited inside the body have produced some ARS effects only in extremely rare cases.
 * The radiation must be penetrating (i.e., able to reach the internal organs).
 * High energy X-rays, gamma rays, and neutrons are penetrating radiations.
 * The entire body (or a significant portion of it) must have received the dose3.
 * Most radiation injuries are local, frequently involving the hands, and these local injuries seldom cause classical signs of ARS.
 * The dose must have been delivered in a short time (usually a matter of minutes).
 * Fractionated doses are often used in radiation therapy. These are large total doses delivered in small daily amounts over a period of time. Fractionated doses are less effective at inducing ARS than a single dose of the same magnitude.