Dependence on age at intake of committed dose equivalents from radionuclides

Doses from radon and its decay products to children

This paper considers doses from radon and decay products when inhaled or ingested by one year old infants and by ten year old children. Doses from decay products deposited on skin are also discussed. For inhalation and ingestion, the general pattern of doses to organs is broadly similar to that in adults. Much the largest doses are received by the organ of intake (respiratory tract and stomach respectively). Otherwise, tissues with higher fat content tend to receive somewhat higher doses from radon gas than other tissues. Dose coefficients (dose per unit intake factors) for children are generally larger than those for adults. However, total annual doses are more similar across the age groups because of smaller intakes of air and water by children. Radon decay products deposited on skin may be able to induce skin cancer. However, the location of the sensitive cells is not known with certainty and they may lie too deep to receive significant dose. If they are irradiated, it is likely that doses to children would be larger than for adults. The radiological significance of doses to children is discussed.

Cancer near nuclear installations

The OPCS report on cancer incidence and mortality in the vicinity of nuclear installations in England and Wales provides a mass of information that is so large that it should be possible to detect quite small changes in disease levels with considerable confidence. The data on cancer mortality are less subject to selective bias than the registration data on which incidence rates are based, and they provide the firmest grounds on which evidence of any effect can be obtained. These data show conclusively that there has been no general increase in cancer mortality in the vicinity of nuclear installations in a 22-year period beginning several years after the opening of the installations that have released the largest amounts of radionuclides to the environment. On the contrary, the mortality from cancer has tended to be lower in the LAAs in the vicinity of nuclear installations than in control LAAs selected for their presumed comparability with the former. This is unlikely to be due to a protective effect of ionizing radiation and suggests that, despite the efforts that were made to choose comparable control areas, there were non-installation differences between the populations relevant to the risk of dying from one or other type of cancer. Detailed examination of the few types of cancer that were relatively more common in the installation areas suggest that several of the differences were most likely to be due to chance, diagnostic artefacts or social factors rather than to any hazard specifically related to the installations. One disease provides a possible exception: namely, leukaemia in the age group 0-24 years. Two other diseases need further investigation, multiple myeloma and Hodgkin's disease in the older age group 25-74 years. The excess mortality rates recorded from these cancers were not large, and it has yet to be established that they are not due to general confounding by other environmental or socio-economic factors.

Estimation of age-dependent internal dose from radiopharmaceuticals

The age-dependence of the radiation dose absorbed in a target organ or the total body is determined by the mass, size, shape and separation of the organs as well as by the metabolic behaviour of the radionuclide compound. Using values of the specific absorbed dose for adults, the age-dependent effective dose equivalents for 28 radiopharmaceuticals (62 radionuclides) were calculated by modifying the above mentioned values, considering radiation type, organ mass and source-target separation. From the results, the currently used mathematical models for the modification of values of specific absorbed doses in the adult prove to be of sufficient accuracy. In comparison with the few available values calculated by Monte Carlo-techniques, our method overestimates the specific absorbed fractions by a factor of four in the least favourable case. For practical radionuclide dose estimates, these deviations are of minor importance as long as the availability of reliable information on the metabolic behaviour of radionuclide compounds and radiopharmaceuticals as a function of age is extremely limited. Considering, however, both the parenteral administration and the short half-life of radionuclides used in paediatric nuclear medicine, this uncertainty in regard to the gastrointestinal absorption and the biological half-lives is of little consequence for the results of absorbed dose calculations.