I068] Radiation effects on the embryo and fetus

Abstract

The effects of in utero radiation should not be confused with heritable effects that can manifest by irradiating germ cells (oocytes or spermatocytes) before conception, causing chromosomal aberrations and/or mutations in the genes themselves. These (stochastic) genetic effects have been documented in animals and insects, but there is no epidemiological evidence of excess heritable disease in the offspring of humans irradiated before conception. The irradiation of somatic cells of the embryo/fetus can cause both tissue injuries and stochastic effects. Tissue injuries are dependent on the fetal stage of development and have been documented in irradiated cohorts of Hiroshima/Nagasaki atomic bomb survivors and residents around Chernobyl and the Mayak Plant/Techa River in the Southern Urals, as well as after medical radiation. According to the 2013 US National Council on Radiation Protection and Measurements Report 174, embryo lethality can occur in the pre-implantation period at doses above 100 mGy; malformations (such as microcephaly, micrognathia and cleft palate) may occur during organogenesis above 100 mGy, and severe mental retardation, in the weeks 8–25th post conception, with a dose threshold of 300 mGy. The most sensitive period is the 8–15th week, where a decrease of up to 30 IQ units has been observed. As for radiation-induced stochastic effects, although cancer has been observed for in utero irradiated cohorts from Hiroshima/Nagasaki and Southern Urals, the numbers are small; it is not known which are the most vulnerable gestation periods. However, the cancer life time risk seems lower than that following irradiation during childhood, which in turn is much higher than in adults. On a mechanistic basis, the 2015 International Commission on Radiological Protection Report 131, suggested that because of high competition between the irradiated and non-irradiated stem cells after low doses in utero, the injured stem cells are discarded before birth, thus yielding a low cancer risk. During childhood growth, stem cell competition is less stringent (higher risk) as the stem cell/niche units increase in number to cope with the increase in tissue volume, an unnecessary mechanism in adulthood (lower risk). The presentation will end showing typical fetal doses in medical radiation procedures.