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20 Cards in this Set
- Front
- Back
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Stochastic Effects |
-Exhibit an increasing incidence of response-not severity with increasing dose. -Probability or frequency of the biologic response to radiation as a function of radiation dose. Diseases incidence increase proportionally with dose, and there is no threshold -our radiation protection guides are based on the stochastic effects of radiation and on linear, non threshold dose-response relationship |
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Local Tissue Effects (Skin) |
-In addition to the deterministic effects of erythema and desquamation and late-developing carcinoma, chronic irradiation of the skin can result in severe nonmalignant changes -Radiodermatitis |
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Local Tissue Effects (Chromosomes) |
-Irradiation od blood-forming organs can produce hematologic depression as a deterministic response or leukemia as a stochastic response. -Low dose of radiation can produce chromosome aberrations that may not be apparent until many years after radiation exposure. -Occurs because of radiation damage to the lymphocytic stem cells. These cells may not be stimulated into replication an maturation for many years. |
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Local Tissue Effects (Cataracts) |
-The radiosensitivity of the lens of the eye is age dependent. As age of the individual increases, the radiation effect becomes greater and the latent period becomes shorter. -Most investigators would suggest that the threshold after an acute x-ray exposure is approximately 2 Gyt 200 rad -Occupational exposures to the lens of the eye are to low to require protective lens shields for radiologic technologists. It is nearly impossible for a medical radiation worker to reach the threshold dose |
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Life-Span Shortening |
-After both acute and chronic radiation exposure that show that irradiated animals die young. -Shows that the relationship between life-span shortening and dose is apparently linear, non threshold -At worst humans can expect a reduced lifespan of approximately 10 days every 10 mGyt -Radiation worker 12 days lost -Radiation-induced life-span shortening is nonspecific, it occurs simply as accelerated premature aging and death |
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Risk Estimates (3) |
-Relative risk -Hormesis -Excess Risk -Absolue Risk -The stochastic effects are also easy to observe, its nearly impossible to associate particular late response with previous radiation exposure -Consequently, precise dose-response relationships are often not possible to formulate, and we therefore resort risk estimates. |
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Relative Risk |
-Is computed by comparing the number of persons in the exposed population showing a given stochastic effect with the number in an unexposed population who show the same stochastic effect. -A relative risk of 1.0 indicates no risk at all -1.5 indicates that the frequency of a late response is 50% higher in the irradiated population than in the non irradiated population |
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Radiation Hormesis |
- Some evidence supports the principle of radiation hormesis. -Suggests that low levels of radiation--less than approximately 100mGyt (10) are good for you |
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Radiation-Induced Leukemia |
-Is considered to have a latent period of 4 to 7 years and an at risk period of 20 years |
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Radiation induced Cancer |
Its not possible to link any case of caner to a previous radiation exposure because cancer is so common. -Approximately 20% of all death are caused by cancer; Therefore any radiation induced cancers are obscured -Radiation-induced skin cancer follows a threshold dose response relationship. |
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Radiation induced Cancer Part 2 |
-Now known that radiation exposure from radon in the mines contributed to the incidence of lunch caner in miners. -The exposure in these mines occurred because of the high concentration of uranium ore, -One of the decay products of uranium is radon |
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Radiation Induced cancer part 3 |
-More than 4000 uranium miners have been observed, they have received estimated dose to lung tissue as high as 30 Gyt (300 rad) -Relative risk was approximately 8:1 -Smoking uranium miners have a relative risk of approximately 20:1 -Americans smoke less and less -One result of this trend is that radon exposure is now the leading cause of lung cancer -42,000 cases of lung cancer each year or radon induced. |
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Nuclear incidents |
-Three mile island incident -Chernobyl nuclear power plant -The fukushima nuclear plant |
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Bier Committee |
The Committee on the biologic effects of ionizing radiation |
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Radiation and pregnancy |
-Before pregnancy concern is interrupted fertility -During concern is directed to possible congenital effects in newborns -post pregnancy are related to suspected genetic effects |
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Irradiation in Utero |
-concerns two types=that of the radiation worker and of the patient -All Observations point to the first trimester during pregnancy as the most radiosensitive -Within first 2 weeks dos pronounced effect of a high radiation dose is prenatal death which manifests as a spontaneous abortion. |
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Irradiation in utero 2 |
-effects are time related, and radiation dose related -Include prenatal death, neonatal death, congenital amoralities, malignancy induction, general impairment of growth, genetic effects, and mental retardation. |
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Major Organogenesis |
Major Organogenesis= Period from 2nd through 12 week, two effects may occur -Skeletal and oran abnormalities -As major organogenesis continues, congenital abnormalities of the CNS may be observed if the pregnancy is carried to term |
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Irradiation in utero 3 |
-Irradiation in utero, principally during the period of major organogenesis, has been associated with microcephaly (Small head) and mental retardation. -100mGyt (10 rad) to fetus is rarely occurs in radiology, essentially possible only during fluoroscopy and CT -not radiography or nuclear med |
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Genetic Effects |
essentially all the data indicating that radiation causes genetic effects have come from large scale experiments with flies or mice -We do not have any data that suggest that radiation induced genetic effects occur in humans. |
