Section 8 Whole-Body Radiation Effects Answers and
Feedback
1. ANSWER: A-TRUE, B-FALSE, C-FALSE, D-FALSE
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.
8. ANSWER: A-FALSE, B-FALSE, C-TRUE, D-FALSE, E-TRUE
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.
10. ANSWER: A-TRUE, B-TRUE, C-TRUE, D-TRUE
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