Low-Dose X-Radiation and Congenital Anomalies

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  • 低線量X線被曝と先天異常

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Among radiation effects on developing embryos and fetuses, occurrence of germinal mutation due to exposure of the gonads and postnatal manifestation of neoplasms are considered to be stochastic effects from the aspect of radiation protection. On the other hand, somatic effects such as teratogenic and embryo-toxic effects can be regarded as nonstochastic ones with threshold doses. In experimental teratological studies with mice and rats, the lowest radiation doses for manifestation of the non-stochastic somatic effects which have been recognized so far are:5 rad for resorption of preimplantation embryos; 5-10 rad for acute cytological changes such as pyknosis, cytoplasmic degeneration and mitotic delay; 5 rad for increasing frequency of spontaneous minor anomalies of the skeleton; 15-20 rad for malformations of the eye, brain and spinal cord; 20-25 rad for histogenetic and functional disorders of the central nervous system; and 20-25 rad for impaired fertility. Pregnant women who are subject to X-ray examinations are much concerned about potential hazard of radiation to their offspring in utero. The above experimental findings suggest that the possibility of non-stochastic somatic effects of diagnostic radiation on human embryos and fetuses is extremely low, and probably negligible, given the proper dose control measures. Possible effects which should be considered for risk evaluation of diagndstic exposure are two stochastic effects, carcinogenic and mutagenic.

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