• Section 8 Whole-Body Radiation Effects Answers and Feedback

  • Section 8 Whole-Body Radiation Effects Answers and Feedback 

    FEEDBACK: Lymphocytes from a blood sample can be stimulated to divide, and chromosomal aberrations can be scored at the first mitosis. The number of aberrations reflects the average effective total body dose. Option A is True. The aberrations scored are of the exchange type, such as dicentrics, which require breaks in two chromosomes, so that the relation to dose is linear-quadratic. Hence, option D is False. The dose that can be detected depends on how many cells are scored, but for practical purposes, 25 cGy is the lowest dose that can be detected. Option B is False. Lymphocytes are very radiosensitive, die an interphase death, and disappear quickly after a large dose. A few days after exposure to 10 Gy, there would be few lymphocytes in circulation, so the system could not be used to assess dose. In any case, the person would have died a gastrointestinal death before 3 weeks. Option C is False. 

    2. ANSWER: C
    FEEDBACK: In the few humans who have died a gastrointestinal death as a consequence of total body irradiation, it is the small intestine that is most completely denuded. The correct option is C. Small intestine 

    3. ANSWER: B
    FEEDBACK: Xeroderma pigmentosum is characterized by sensitivity to ultraviolet radiation but not to x-rays. Bloom syndrome and Fanconi anemia both exhibit genomic instability but are not particularly sensitive to either x-rays or ultraviolet radiation. The characteristic of ataxia telangiectasia is sensitivity to xrays but not to ultraviolet radiation. The correct option is B. 

    4. ANSWER: C
    FEEDBACK: A total body dose in the range of 0.75–1.25 Gy results in nausea in 5%–30% of persons exposed. At higher doses in the range of 1.25–3.00 Gy, the prevalence increases to 20%–70%. Above 5.3 Gy, moderate to severe nausea is expected in 50%–90% of persons exposed. The correct option is C. 

    5. ANSWER: B
    FEEDBACK: The lymphocyte count would be decreased by a dose of 0.5 Gy. A transient early erythema may be produced by a dose of 2 Gy, with 6 Gy required for a robust erythema. Temporary epilation occurs after a dose of 3 Gy and permanent epilation after 7 Gy. A dose of 3.5 Gy or more is required to produce sterility in the female. The correct option is B. 

    6. ANSWER: 1-D, 2-A, 3-C, 4-B
    FEEDBACK: Three of the four options in this question relate to death by total body irradiation at differing dose levels. The LD 50/60 refers to the death of 50% of the exposed population in 60 days due to failure of the hematopoietic system. Its value is about 3–4 Gy. C matches with 4. LD 50/5 refers to the dose required to kill humans by denuding the lining of the gastrointestinal tract. Its value is about 10 Gy. B matches with 3. Only a few examples of death by the cerebrovascular syndrome have ever been seen in humans. Death occurs in about 48 hours, and the dose required is about 100 Gy. A matches with 1. The

    fourth option involves hereditary effects (i.e., effects in offspring due to irradiation of parents). The dose required to double the natural or spontaneous mutation rate is about 1 Gy. D matches with 2. 

    7. ANSWER: B
    FEEDBACK: The minimum dose of x rays in an acute exposure likely to produce a vision-impairing cataract is 2 Gy. Dicentric chromosomal aberrations in stimulated human peripheral lymphocytes can be observed at any dose above about 0.25 Gy. Option B is correct. A transient early erythema may be produced by a dose of about 2 Gy, and a robust erythema requires 6 Gy. Ataxia is not a likely result of any dose, except perhaps hundreds of grays. The risk estimate for radiation-induced cancer is 8%/Gy for an acute exposure. A 25 % increase would require 25 /8 Gy, or 3.1 Gy.

    FEEDBACK: Vomiting and other GI symptoms in the majority of individuals exposed require a dose of several GY.Option A is false. Diarrhea indicates a supralethal dose (i.e., a dose in excess of 3–4 Gy). Option B is false.  Option C is true because temporary sterility in males occurs after a dose as low as 0.15 Gy. However, permanent sterility in females requires a dose of 3 Gy or more. Option D is false. A decrease in lymphocyte count would be observed at a dose as low as 0.5 Gy. Option E is true.

    9. ANSWER: A
    FEEDBACK: The dose that would kill 50% of a population as the result of failure of the hematopoietic system (i.e., LD 50/60) is 3–4 Gy. Option A is correct. Seizures are not a feature of any radiation dose short of the central nervous system/cerebrovascular syndrome, which requires a dose in excess of 100 Gy. Option B is false. The nadir of the white blood cell count, determined by the lifetime of mature circulating cells, is several weeks following irradiation. Option C is false. Bone marrow transplants cannot save persons exposed to doses in excess of about 10 Gy, because they will die a gastrointestinal death. Option D is false.

    FEEDBACK: A dirty bomb is a dispersal device that causes purposeful dissemination of radioactive material over a wide area without a nuclear detonation. Potential sources of radioactive material for a dirty bomb include naturally occurring radionuclides (e.g., radium, uranium, thorium), products of the nuclear fuel cycle, radioisotopes used in medicine, components of military systems, and radiation sources used in industry. Highly radioactive material such as nuclear fuel rods, cobalt-60 teletherapy sources, and industrial radiography units could deliver significant whole body exposure to those present, resulting in acute radiation syndrome. Contaminated-injured patients are anticipated from an explosive device that releases radioactive material. Patients with large amounts of radioactive contamination pose an exposure hazard to medical personnel. As an act of terrorism, the primary purpose of a dirty bomb is to inflict fear, destroy the sense of well-being, and disrupt community function. All options are true. 

    Return to Syllabus