The paper deals with one of the most urgent aspects of irradiation hygiene, namely assessment of risk for irradiation-induced cancers of the thyroid. A model is described to predict high mortality rates of thyroidal cancer in the population due to the catastrophe at the Chernobyl Atomic Power Station. With the model, life-time risk rates involving sex and age at the moment of irradiation, as well as an irradiation mode.
This review presents the actual state of knowledge about medical dangers of a radioactive fall-out. Concepts for the estimation of accidental incorporation, as well as effects and risks that are known to occur after incorporation of radionuclides are discussed. Special attention is paid to the following topics: effect of radioiodine on the thyroid gland, effect of radio-cesium on whole body burden, alpha-emitting particles (plutonium) with deposition in the airways, association of osteotrope radionuclides (strontium) with malignomas of the skeleton and finally prophylaxis with iodine to prevent damage of the thyroid.
The thyroid doses received by the juvenile population of Belarus following the Chernobyl accident ranged up to about 10 Gy. The thyroid cancer risk estimate recommended in NCRP Report No. 80 was used to predict the number of thyroid cancer cases among children during 1990-1992 in selected Belarussian regions and cities. The results obtained using this risk estimate show an excess of thyroid cancer cases being registered vs. the predicted cases. Thyroid cancer incidence rate among boys under investigation is higher than among girls in the postaccident period. The excess of the observed over the expected incidence in the general juvenile population is caused by the high thyroid cancer incidence rate among boys. These results, which can be considered part of the first stage of a thorough thyroid cancer risk estimation after the Chernobyl accident, demonstrate the critical need to complete these studies in depth.
On April 26, 1986, after partial fusion and confining loss by explosion of a nuclear reactor, 5 x 10(7) Ci of radionuclides escaped from Chernobyl. Three years later, maps show contamination by radioactive isotopes (formed during that period) of 21,000 km2 of Soviet soil, mainly in Byelorussia and part of the Ukraine. Decontamination measures have not been effective to date and 135,000 persons are being followed medically, taking into account the radioactive doses they received. An initial excess of morbidity from solid tumors has been noted much sooner than in the case of Hiroshima and Nagasaki, but its significance is in dispute. Three years later, only the extent of the ecologic disaster caused by the radioactive contamination can be confirmed. It is too early to draw conclusions about radiation-induced carcinogenesis for the contaminated population.
During the past twelve months much media attention has been focused on the plight of the children affected by the Chernobyl nuclear disaster in the Soviet Union. The visit to Australia by several groups of these children during 1991 has heightened community interest in the innocent victims of the world's worst nuclear accident. As medical adviser for one of these visits, I saw how some of the children of Chernobyl benefited from their holiday away from radioactivity.