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useful modality for medical imaging and an effective means for treating a variety of
conditions from acne to malignancies. However, some of the side effects of radiation
became known within a few years. Some early radiologists developed radiation skin
injury and leukemia from their exposure to ionizing radiation.
Since 1940, there have been over 300 significant radiation accidents in the United States
alone. These include both medical and industrial errors, as well as accidents involving the
production and storage of nuclear weapons. Some of the most significant worldwide
events associated with radiation injury are described below.
Hiroshima and Nagasaki, Japan — 1945
The atomic bomb blasts over Hiroshima and Nagasaki in 1945 during World War II
resulted in massive firestorms that obliterated much of the city. They also provided
information on the medical effects of uncontrolled ionizing radiation over a wide dose
range among those casualties who initially survived the blast and firestorm. The bomb
detonated over Hiroshima was equivalent to 15,000 tons (15 KT) of TNT, while the
Nagasaki weapon was equivalent to 22 KT of TNT.
It has been estimated that 50% of those exposed to a 2.7–3.1 Gray (Gy) bone marrow
dose died within 60 days from their radiation exposure, as little medical assistance was
available. Radioactive fallout was very limited, because both of the detonations were
airbursts, in which the actual fireball does not reach the ground. The estimates of
maximum dose due to fallout are 1–3 centigray (cGy) in Hiroshima and 20–40 cGy in
Nagasaki.
The principal effects of radiation in unborn infants in Hiroshima and Nagasaki were
small head size (microcephaly) and mental retardation. Of the 1,600 children exposed
before birth who were followed, 30 were found to have severe mental retardation. Those
with severe mental retardation were noted to have received radiation exposure between 8
weeks and 25 weeks gestation. The most sensitive time of the gestational period was
found to be 8–15 weeks after conception.
Ionizing radiation is a relatively weak carcinogen. Among 86,000 atomic-bomb survivors
at Hiroshima and Nagasaki followed from 1950 to 1990, there were 7,578 deaths from
solid cancer (versus 7,244 expected) and 249 deaths from leukemia (versus 162
expected), representing 421 additional deaths from cancer. The minimum elapsed time
between radiation exposure and clinical disease was 2–3 years for leukemia, 3–4 years
for bone cancer, 4–5 years for thyroid cancer, and 10 years for other solid tumors.
Mayak, Russia, Former Soviet Union — 1948-1990
The Mayak Production Association (Mayak) is an industrial complex in the Southern
Urals of Russia, where the former Soviet Union produced tons of plutonium for nuclear
weapons. Between 1948 and 1956, radioactive waste was poured directly into the Techa
River, which was the source of drinking water for many villages. It is reported that
124,000 people were exposed to medium and high levels of radiation. In 1957, one of the
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