486 Obstetrics and Gynecology Board Review •••
❍ What are the acute effects of whole-body radiation?
Three types of syndromes can develop depending on the dose:
(1) Cerebrovascular occurring at high doses (10,000 cGy) with death occurring within 1 to 2 hours.
(2) Gastrointestinal injury at moderate doses (500–1200 cGy) resulting in destruction of the gastrointestinal tract
and death within several days.
(3) Hematopoetic injury with doses of 250–500 cGy with death occurring within several weeks.
❍ What is the approximate mean lethal whole-body dose for humans?
Approximately 400 cGy.
❍ Does radiation exposure lead to new mutations or does it just increase the incidence of those mutations that
occur spontaneously in a population?
It increases the incidence of the range of mutations that occur spontaneously.
❍ What is the approximate “doubling dose” of radiation that is required to double the spontaneous mutation
rate in humans?
The best estimate based on mouse data is 100 cGy. The incidence of mutations is essentially a linear function of
dose.
❍ What is meant by the “oxygen enhancement effect”?
Well-oxygenated cells are more sensitive to irradiation because the oxygen molecules react with free radicals that affect
biologic damage. That is, a small amount of oxygen will potentiate the effect of irradiation. Inadequately oxygenated
cells have a significant impact on the radiosensitivity of a tumor, often necessitating higher doses of radiation.
❍ What is the latency period between exposure to radiation and the development of radiation-induced cancer
and leukemia in humans?
The latency period is usually long with leukemias typically occurring 5 to 7 years following exposure and solid
lesions developing after 30 to 40 years.
❍ What concepts have been explored to potentiate radiation therapy and enhance tumor kill?
(1) Reoxygenation of hypoxic tumor cells between doses of radiation.
(2) The use of radiation sensitizers that selectively increases the effect of ionizing radiation on a tumor.
(3) Hypoxic cell sensitizing compounds that, when administered, sensitize hypoxic cells to radiation.
(4) Bioreductive drugs that specifically kill cells deficient in oxygen.
❍ What do actinomycin D, doxorubicin, mitomycin C, 5-fluorourasil, cyclophosphamide, methotrexate,
bleomycin, and cisplatin have in common?
They are all cytotoxic chemotherapeutic agents that have been shown to interact with radiation to maximize tumor
cell killing.
❍ What role does hyperthermia play in radiation therapy?
Heat selectively kills cells that are hypoxic, nutritionally deficient, and acidosis all being hallmarks of tumor cells.
Temperatures above 42.5°C have been demonstrated to enhance the effects of cytotoxic agents.