• Section 5 Radiation Carcinogenesis Answers and Feedback

  • Section 5 Radiation Carcinogensis Answers and Feedback 

    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. 

    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. 

    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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