RADIATION EFFECTS AFTER EXPOSURE DURING P RENATAL DEVELOPMENT

The embryo and fetus are very radiosensitive during the total prenatal development period. The quality and extent of radiation effects depen d strongly on the developmental stage at which the exposure occurs. Du ring the preimplantation period radiation exposure can cause death of the embryo after radiation doses of 0.2 Gy and higher. Malformations a re only observed in very rare cases when genetic predispositions exist . Macroscopic-anatomical malformations are induced only after irradiat ion during the major organogenesis. On the basis of experimental data with mammals it is assumed that a radiation dose of about 0.2 Gy doubl es the malformation risk. Studies in humans give rise to the assumptio n that the human embryo is more radioresistant than the embryos of mic e and rats. Radiation exposure during the major organogenesis and the early fetal period lead to disturbances in the growth and developmenta l processes. During early fetogenesis (week 8-15 post coruption) high radiosensitivity exists for the development of the central nervous sys tem. Radiation doses of 1 Gy cause severe mental retardation in about 50 % of exposed fetuses. Analysis of the dose-effect curves shows that there is probably a dose-effect curve with a threshold for this effec t. It must be taken into account that radiation exposure during the fe tal period also induces cancer. The studies, however, do not allow qua ntitative estimate of this radiation risk at present. It is therefore generally assumed that the risk is about the same level as for childre n.