RADIATION/NUCLEAR
EXPOSURE AND THYROID CANCER – LESSONS LEARNED FROM TWO NUCLEAR PLANT ACCIDENTS (Chernobyl
[Ukraine] 1986 and Fujushima [Japan] 2011)
In 1986,
after the accident at the nuclear power plant at Chernobyl (Ukraine) huge
amounts of radioactivity was released in the atmosphere, including large
amounts of radioactive iodines. The radiation dose to the thyroid gland was
high in Belarus, Ukraine, and South Russia since the uptake of radioiodines in
the thyroid gland was high due to iodine deficiency and no iodine prophylaxis.
Because of wind during the days after the accident, the radiation cloud spread
over large territories in extended areas of Europe. Local authorities failed to
organize a timely response to the disaster. The first cases of thyroid cancer
were reported in contaminated young children in 1990, only 4 years after the
accident in Minks and Kiev centers. The incidence of childhood thyroid cancer
then rapidly increased and in 1995 reached 40 per million (Bellarus). It is
estimated that 7000 thyroid cancer cases occurred among the 2 million highly contaminated
subjects who were younger than 18 years at the time of accident. In children, a
strong correlation was found between the dose of radiation delivered to the
thyroid and the risk of developing thyroid cancer.
On March
11, 2011, during the Fukushima nuclear plant accident (Japan), large amounts of
radioactive isotopes, including I-131, were released in the atmosphere. However,
the radiation dose to the thyroid gland was low because the authorities ordered
shielding, evacuation from the most contaminated territories, and food
restriction. Furthermore, the thyroid uptake of iodine was low, in relation to
the high iodine alimentary intake. During the first 5 years following the
accident, there was no increased incidence of clinical thyroid cancers (1 to 5
per million children). In those who developed a thyroid cancer, the radiation
dose to the thyroid was low and there is no evidence that the incidence of
thyroid cancer is increasing with time.
The
comparison of these two recent nuclear plant accidents showed that it is extremely
important to avoid any thyroid irradiation – especially in children – in case
of atmospheric contamination by means of:
-shielding
-food
restrictions
-evacuation
from highly contaminated areas
-administration
of large amounts of stable iodine
Stable
iodine, administered as potassium iodine (KI) inhibits the thyroid uptake of
radioactive iodine by more than 98 % if it is administered several hours before
contamination, by 90 % at the time of contamination, and by 50 % if it is given
6 hours after the accident. Uptake will be low during 48 – 72 hours and then
will re-increase. Stable iodine (KI) prophylaxis should be administered in
priority to children and pregnant women. It is no recommended for people over
60 years or those with cardiovascular disease. In France, KI is distributed to
the population living within 10 kilometers of one of the 19 French nuclear
power plants.
Mechanical devices
(such as filters, isolating barriers) are of crucial importance in preventing or
limiting atmospheric contamination. Western nuclear reactors are fitted with these
devices (fliters/isolating barriers), but these were not present at the Chernobyl
nuclear plant. These devices will ensure a delay of several hours between a
serious incident and the release of radioactive material into the atmosphere. Public
authorities must capitalize on this time interval to organize iodine prophylaxis.
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