• Section 7 Radiation Effects on the Developing Embryo and Fetus Answers and Feedback

  • Section 7 Radiation Effects on the Developing Embryo and Fetus Answers and Feedback 

    1. ANSWER: A
    FEEDBACK: The risk estimate for the hereditary effects of radiation, based on a doubling dose of 1 Gy, plus an allowance for multifactorial diseases, is estimated by the ICRP to be 0.2%/Sv. (For x-rays, sieverts and grays are interchangeable units, since the radiation weighting factor for x-rays is unity.) The risk for a hereditary effect from an exposure of 0.1 Gy is therefore 0.2/100 × 0.1 = 2 × 10–4, a risk of 2 in 10,000. The correct option is A, less than 1 in 1,000. 

    FEEDBACK: Radiation-induced abortions after a 2-Gy exposure are very likely during weeks 0–2 of gestation, but are unlikely during weeks 8–15. Option A is False. During weeks 0–2, radiation-induced abortions are likely, but congenital abnormalities are unlikely to occur until weeks 2–6. Option B is False. Although not high, the risk of mental retardation may occur during weeks 15 –25 (a risk level of about 10%/Sv). Option C is True. The risk of mental retardation is as much as 40%/Sv during weeks 8–15. During the period of organogenesis (2–6 weeks of gestation), congenital abnormalities are likely after a dose of 2 Gy. Option D is True. 

    3. ANSWER: 1-B, 2-A, 3-C
    FEEDBACK: Animal experiments indicate that exposure to radiation during organogenesis leads to a wide spectrum of malformations. B matches with 1. During pre-implantation, radiation appears to have an all-or-nothing effect; either the newly fertilized egg is killed, or it develops normally. Growth retardation and malformations do not result from irradiation at this time. A matches with 2. There is an increased risk of cancer due to exposure in utero. C matches with 3. 

    FEEDBACK: An accident situation in which injuries are possible justifies the small risks associated with diagnostic x rays. Option A is False. A therapeutic abortion would not be justified. Option B is False. On the basis of the Japanese survivors’ data, 8–15 weeks is the sensitive period for reduced head diameter and mental retardation. The doses are not large enough for this to be very likely, but if a radiation-induced defect occurred, it would involve the central nervous system. Option C is True. On the basis of the case-control studies of Stewart et al, even a few radiographs during pregnancy increase the risk of leukemia and childhood cancer. Option D is True. The dose to the fetus would be considerably less than 0.1 Gy. Option E is False. 

    FEEDBACK: Intrauterine death occurs as a result of irradiation during pre-implantation (0–10 days), and neonatal death (i.e., death at or about the time of birth) occurs because of irradiation during organogenesis (10 days to 6 weeks). Irradiation at 18 weeks is too late for either of these. Options A and B are False. The data from persons exposed in utero at Hiroshima and Nagasaki show that irradiation to a sufficient dose may produce microcephaly (reduced head diameter) and mental retardation. The most sensitive time interval for these effects was 8–15 weeks. There was a less sensitive interval at 15 –25 weeks. Option C is True. The case-control studies of Stewart et al showed that even a few obstetric radiographs could lead to an elevation of risk of leukemia and childhood cancer. Option D is True. 

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