Radiation doses to the embryo and fetus following intakes of radionuclides by the mother

An ICRP Task Group on Age-dependent Dosimetry is at present developing models that can be used for calculating doses to the embryo and fetus following intakes by the mother of the most important radionuclides likely to be released from nuclear facilities. Human data on which dosimetric models can be based are available for only a few radionuclides and for most the results of animal experiments must be used, though even here data are frequently very limited. In the extrapolation of animal data to man extreme care is needed; particular problems in the development of dosimetric models for the embryo and fetus include the rapidity of growth, the varying progress of organ development in different species, and the presence of several types of placentae in different species, all of which provide a selective but potentially different barrier between maternal and fetal blood. Consideration also needs to be given to the period over which the intake occurs and the dose is calculated. A general approach is envisaged by the Task Group which will be modified when more specific information is available. For the embryo, to two months after conception, it is assumed that the dose will be the same as that to the uterus. For the fetus doses are based on relative concentrations in fetal and maternal tissues. It is envisaged that doses will be calculated following acute and chronic intakes by the mother both before and after conception. The paper describes the models being developed by the Task Group, the results of some preliminary calculations and the use of more specific biokinetic information where it is available. In general, the results indicate that for many radionuclides doses to the fetus will be less than those to the mother, although for isotopes of caesium and iodine the dose to the fetus is expected to be similar to that of the mother. There is little suggestion that fetal doses will be significantly higher than maternal doses.