II.

Acute Effects

High whole-body doses of radiation produce a characteristic pattern of injury. Doses are measured in grays or rads, 1 gray being equal to the dose absorbed when one kilogram of matter absorbs one joule of ionizing radiation, and 100 rads being equal to 1 gray. Doses of more than 40 grays severely damage the human vascular system, causing cerebral edema, which leads to profound shock and neurological disturbances; death occurs within 48 hours. Whole-body doses of 10 to 40 grays cause less severe vascular damage, but they lead to a loss of fluids and electrolytes into the intercellular spaces and the gastrointestinal tract; death occurs within ten days as a result of fluid and electrolyte imbalance, severe bone-marrow damage, and terminal infection. Absorbed doses of 1.5 to 10 grays cause destruction of human bone marrow, leading to infection and hemorrhage; death, if it occurs, can be expected about four to five weeks after exposure. Currently only the effects of these lower doses can be treated effectively; but if untreated, half the persons receiving as little as 3 to 3.25 grays to the bone marrow will die.

Exposure of small areas of the body—the most frequent kind of radiation accident—leads to localized tissue damage. Damage to the blood vessels in exposed areas causes disturbed organ function and, at higher doses, necrosis (localized tissue death) and gangrene.

Injury from internally deposited radiation sources is not likely to cause acute effects but, rather, delayed phenomena, depending on the target organ and on the half-life, radiation characteristics, and biochemical behavior of the radiation source. Consequences may include degeneration or destruction of the irradiated tissue and the initiation of cancer.