Section 5 Radiation Carcinogensis Answers and
1. ANSWER: 1-A, 2-B, 3-D, 4-E, 5-C
FEEDBACK: An excess incidence of leukemia was observed in patients with
ankylosing spondylitis treated with x-rays for the relief of pain. A matches with 1. An excess of
breast cancer was observed in patients who underwent fluoroscopy many times
during the management of tuberculosis, first reported from Canada and later
repeated in a New England study. B
matches with 2. Thyroid tumors, both benign and malignant, were
observed in the inhabitants of the Marshall Islands in the Pacific as a result
of fallout from the testing of nuclear weapons. C matches with 5. An excess of lung cancer is observed in
underground miners, including uranium miners, who breathe radon, which concentrates
in the environment of the mine. Radon is a noble gas with a half-life of about
3 days. It decays to solid radioactive isotopes that stick to particles of dust
and are deposited in the bronchi and lungs. These radionuclides emit alpha
particles that irradiate the bronchial epithelium and may cause lung cancer. D matches with 3. Women employed
as dial painters ingested radium by licking their brushes for the application
of luminous paint to watches. Bone sarcomas and carcinomas of epithelial cells
lining the paranasal sinuses and nasopharynx were observed in this exposed
population. E matches with 4.
2. ANSWER: 1-D, 2-B, 3-C, 4-A
FEEDBACK: The prostate has a relatively high natural or spontaneous incidence
of cancer in the United States, but a low risk of induction by radiation. D matches with 1. Thyroid cancer
is relatively rare in the population, but both benign and malignant tumors are
induced by radiation, especially in children and young people. B matches with 2. Breast cancer
is relatively common in the U.S. population and is readily induced by radiation.
C matches with 3.
Malignancies in the kidney are rare and do not figure prominently in any of the
major populations exposed to radiation. A
matches with 4.
3. ANSWER: A-FALSE, B-TRUE, C-TRUE, D-FALSE
FEEDBACK: Risk estimates for radiation-induced cancer are based on studies of
exposed populations in which there is a clear dose-related excess of cancer
cases. Good examples include the survivors of the atomic bombs in Hiroshima and
Nagasaki, as well as the women who underwent fluoroscopy many times during the
management of tuberculosis. Options B
and C are True. Patients treated with I-131 show no clear dose-related
excess of cancer or leukemia, nor do populations living near nuclear power
plants. Consequently, neither can be used to obtain risk estimates. Options A and D are False.
4. ANSWER: A-FALSE, B-FALSE, C-TRUE, D-TRUE, E- FALSE
FEEDBACK: Latency is the time between irradiation and the appearance of
malignancy. For leukemia, the latent period is short, on the order of 5–7
years, while for solid tumors the latent period may be as long as 20–50 years. Option A is False; option D is True.
Children are more sensitive than adults for some malignancies, while for
others, there appears to be little difference with age. However, children are
certainly not less sensitive than adults. Option
B is False. Radiation induces benign as well as malignant tumors
(thyroid tumors are the best example). Option
C is True. The ICRP risk estimate for radiation-induced cancer in a
working population at low dose and dose rate is 4%/Gy. A dose of 0.1Gy would result
in a cancer incidence of 0.4%, not 10%. Option
E is False.
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