Higher cancer risk continues
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NIH study finds that thyroid cancer risk for
those who were children and adolescents when exposed to fallout has not
yet begun to decline
Nearly 25 years after the accident
at the Chernobyl nuclear power plant in Ukraine, exposure to radioactive
iodine-131(I-131, a radioactive isotope) from fallout may be responsible
for thyroid cancers that are still occurring among people who lived in
the Chernobyl area and were children or adolescents at the time of the
accident, researchers say.
An international team of researchers led by
the National Cancer Institute (NCI), part of the National Institutes of
Health found a clear dose-response relationship, in which higher absorption
of radiation from I-131 led to an
increased risk for thyroid cancer that has not seemed to diminish over
The study, which represents the first prospective
examination of thyroid cancer risk in relation to the I-131 doses received
by Chernobyl-area children and adolescents, appeared March 17, 2011, in
the journal Environmental Health Perspectives.
"This study is different from previous
Chernobyl efforts in a number of important ways. First, we based radiation
doses from I-131 on measurements of radioactivity in each individual’s
thyroid within two months of the accident," explained study author
Alina Brenner, M.D., Ph.D., from NCI’s
Radiation Epidemiology Branch. "Second, we identified thyroid
cancers using standardized examination methods. Everyone in the cohort
was screened, irrespective of dose."
The study included over 12,500 participants
who were under 18 years of age at the time of the Chernobyl accident on
April 26, 1986, and lived in one of three Ukrainian oblasts, or provinces,
near the accident site: Chernigov, Zhytomyr, and Kiev. Thyroid radioactivity
levels were measured for each participant within two months of the accident,
and were used to estimate each individual’s I-131 dose. The participants
were screened for thyroid cancer up to four times over 10 years, with the
first screening occurring 12 to 14 years after the accident.
Standard screenings included feeling for growths
in the thyroid glands and an ultrasonographic examination (a procedure
that uses sound waves to image the thyroid gland within the body), and
an independent clinical examination and thyroid exam by an endocrinologist.
Participants were asked to complete a series of questionnaires including
items specifically relevant to thyroid dose estimation. These items
included residential history, milk consumption, and whether they were given
preventive doses of non-radioactive iodine in the two months following
the accident, to help lessen the amount of radioactive iodine that would
be absorbed by the thyroid. Participants with a suspected thyroid
cancer were referred for a biopsy to collect potentially cancerous cells
for microscopic examination. If warranted, participants were also referred
for surgery. In total, 65 of the study participants were diagnosed with
Researchers calculated cancer risk in relation
to how much energy from I-131was absorbed by each person’s thyroid, measured
in grays. A gray is the International System of Units measure of
absorbed radiation. Each additional gray was associated with a twofold
increase in radiation-related thyroid cancer risk.
The researchers found no evidence, during
the study time period, to indicate that the increased cancer risk to those
who lived in the area at the time of the accident is decreasing over time.
However, a separate, previous analysis of atomic bomb survivors and medically
irradiated individuals found cancer risk began to decline about 30 years
after exposure, but was still elevated 40 years later. The researchers
believe that continued follow-up of the participants in the current study
will be necessary to determine when an eventual decline in risk is likely
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REFERENCE: Brenner AV, Tronko MD, Hatch M, Bogdanova TI, Oliynik VA,
Lubin JH, Zablotska LB, Tereschenko VP, McConnell RJ, Zamotaeva GA, O’Kane
P, Bouville AC, Chaykovskaya LV, Greenebaum E, Paster IP, Shpak VM, Ron
E. I-131 Dose-Response for Incident Thyroid Cancers in Ukraine Related
to the Chornobyl Accident. Mar 17, 2011, EHP, Vol. 119.
Chernobyl Study Says Health Risks Linger
By GARDINER HARRIS
Published: March 17, 2011
Nearly 25 years after the accident at the
Chernobyl nuclear power plant in Ukraine, children and teenagers who drank
contaminated milk or ate affected cheese in the days and weeks after the
explosion still suffer from an increased risk of thyroid
cancer, according to a study released
Thursday by the National
The study confirms earlier research about
the risks of radioactive iodine, which can accumulate in the thyroid gland
and lead to cancer
later. Potassium iodide is often given as a supplement to prevent the
accumulation of the radioactive type in thyroid glands, but Russian authorities
failed to provide the supplement to all those at risk.
Radioactive iodine has a half-life of just
eight days, and it was not thought to be present outside the power plant
in concentrations high enough to cause immediate health problems. But the
isotope was concentrated by cows in milk, and children who drank contaminated
milk or ate affected dairy products are particularly at risk.
An international team of researchers led by
the National Cancer Institute, a federal agency based in Bethesda, Md.,
has been monitoring the health effects of the Chernobyl accident for years.
In the study released Thursday, the team screened 12,500 people who were
under 18-years-old at the time of the 1986 accident and lived in one of
three provinces near the accident site. The subjects’ thyroid glands were
measured for radioactivity within two months of the accident.
Those with the greatest exposures were at
highest risk for developing thyroid cancer in later years, the researchers
found. Sixty-five of the study’s subjects developed thyroid cancer during
the study’s 10 years of screening.
Indeed, the increased risks associated with
exposures to radioactive iodine have yet to show any sign of declining.
Studies done in Japan after World War II suggested that the increased risks
of thyroid cancer began to decline 30 years after the atomic explosions
but remained above normal even 40 years later.
Some of the participants in the Chernobyl
study lived as far as 90 miles from the accident site, demonstrating the
risks of eating or drinking contaminated foods among people who were exposed
to little or no radioactive iodine from the immediate fallout.
"This study confirms the risk of thyroid
cancer from radioactive iodine," Dr. Alina V. Brenner, a radiation
epidemiologist at the cancer institute and a co-author of the study, said
in an interview. "But thyroid cancer is largely a nonlethal cancer.
If detected and treated in a timely manner, they have a good prognosis."
That this study was released in the midst
of the crisis at the stricken Fukushima Daiichi Nuclear Power Station in
Japan was a coincidence. Indeed, government officials scheduled the release
for Thursday because they feared weeks ago that the government might shut
down on Friday as a result of a budget impasse on Capitol Hill.