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Chernobyl 15 years after
After Chernobyl the exposure was to isotopes in fall-out, and apart from inert gas xenon, largest components were radioactive isotopes of iodine.
CHERNOBYL HAS made a chilling contribution to medical history, accounting for the largest group of human cancers associated with a known cause on a known date, ECCO 11 - the European Cancer Conference heard in Lisbon recently.
Nearly 2000 cases of thyroid cancer have been linked to the world's worst nuclear accident which occurred in an Ukrainian city 15 years ago - and the number is still rising.
According to Federation Of European Cancer Societies, Professor Dillwyn Williams, of The Strangeways Research Laboratory, Cambridge University, told the meeting: "Four years after the accident, an excess of thyroid cancers was noted among children who had been exposed to fall-out from the disaster. That increase has continued and new cases are still being seen in those who were children at the time of the accident".
Dr. Elaine Ron, of the US National Cancer Institute, in Bethesda, Maryland, explained: "Following external radiation exposure, the elevated risk of thyroid cancer appears to continue throughout life, but there is some indication that the risk may be highest 15-19 years after exposure.
External radiation is the only well established cause of cancer of the thyroid gland. People under 20 are at a significantly increased risk of thyroid cancer after exposure to isotopes of iodine. It is estimated that in the accident, the Chernobyl-4 reactor released all of the xenon gas, about half of the iodine and caesium and about three to five per cent of the remaining radioactive material.
Professor Williams said: "Exposure to isotopes of iodine gives the thyroid over a 1000 times the average dose to the rest of the body.
The particular sensitivity of children to thyoid cancer after radiation exposure can be linked to a combination of a higher thyroid dose and the biology of thyroid growth - which falls to a very low level in adult life. Few of the patients with thyroid cancer have died, but help is still needed".
Dr. Williams said: "The effects of Chernobyl differed very greatly from those after the atomic bomb explosions. In Japan, the exposure was very largely to whole body radiation from gamma rays and neutrons. After Chernobyl the exposure was to isotopes in fall-out, and apart from the inert gas xenon, the largest components were radioactive isotopes of iodine".
Post Chernobyl cancer risks are not restricted to the thyroid gland the meeting was told. Mr. Victor Chizhikov, of the Cancer Research Center, Kashirskoye, Moscow, reported that a study of former 43 Chernobyl "clean-up" workers had shown them to be at a significantly increased risk of lung cancer.
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