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Rad Protection Ch.9
Stochastic Effects & Late Tissue Reactions of Radiation
| Question | Answer |
|---|---|
| Late Effects | Radiation-induced damage at the cellular level may lead to measurable somatic and hereditary damage in the living organism as a whole later in life. These outcomes are called late effects and are the long-term results of radiation exposure. |
| Examples of measurable late biologic damage: | - Cataracts. - Leukemia. - Genetic mutations. |
| Epidemiology | The science that deals with the incidence, distribution and control of disease in a population. |
| Radiation Dose Response Relationship | - Is demonstrated graphically through a curve that maps the observed effects of radiation exposure in relation to the dose of radiation received. |
| Radiation Dose Response Relationship: | - Information obtained can be used to attempt to predict the risk of occurrence of malignancies in human populations that have been exposed to low levels of ionizing radiation. |
| 2Rdrr = | The observed effects of radiation exposure in relation to dose of radiation received. As the dose increases, so does the effects. |
| Threshold | Is the point a response will occur. |
| Nonthreshold | No dose is safe. |
| LNC | Biologic response is directly proportional to the dose. |
| Lqntc | Estimates the risk associated with low level. |
| S | Therapy to demonstrate high dose. |
| Relationship Dose Response Relationship | - Threshold. - Non-threshold. - Linear non-threshold curve. - Linear-quadratic, non-threshold curve. - Sigmoid or S-shaped (nonlinear) threshold curve. |
| Threshold | - Biologic effects begin to occur only when the threshold level or dose is reached. - A point at which a response or reaction to an increasing stimulation first occurs. |
| Threshold: | - With reference to ionizing radiation, threshold means that below a certain radiation level or dose, no biologic effects are observed. |
| 1.Nonthreshold | 1. Indicates that a radiation absorbed dose of any magnitude has the capability of producing a biologic effect. |
| 2.Nonthreshold | 2.No radiation dose can be considered absolutely safe with the severity of the biologic effects increasing directly with the magnitude of the absorbed dose. |
| 3.Nonthreshold | 3.For the linear nonthreshold curve biologic effect responses will be caused by ionizing radiation in living organisms in a directly proportional manner all the way down to dose levels approaching zero. |
| Which type of dose response relationship curve describes for any dose there is a response? | Nonthreshold. |
| 1.Risk Models Used to Predict Cancer Risk and Heritable Damage in Human Populations: | 1.Stochastic effects (e.g., cancer) and hereditary effects at low-dose levels from low-LET radiation, such as the type of energy used in diagnostic radiology, appear to follow a linear-quadratic nonthreshold curve. |
| 2.Risk Models Used to Predict Cancer Risk and Heritable Damage in Human Populations: | 2.Committee on the Biological Effects of Ionizing Radiation (BEIR) 1980 |
| Somatic Effects | When living organisms that have been exposed to radiation sustain biologic damage, the effects of this exposure are classified as somatic (i.e., body) effects. |
| Stochastic Effects: | The probability that the effect happens depends upon the received dose, but the severity of the effect does not. Example: Occurrence of cancer. |
| Tissue Reactions: | Both the probability and the severity of the effect depend upon the dose. Example: A cataract. |
| __________________ are deterministic | Tissue reactions. |
| Late Somatic Effects | - Effects that appear months or years after exposure to ionizing radiation. - May result from previous whole-body or partial-body acute exposure. - Previous high radiation doses. |
| Late Somatic Effects: | - Long-term low-level doses sustained over several years diagnostic imaging and radiographers. - Natural background exposure. - X-rays and radioactive material used for diagnostic purposes. |
| Late Stochastic Somatic Effect | - Late effects that do not have a threshold and occur in an arbitrary or probabilistic manner. - Severity depends on dose. - PROBABILISTIC. |
| CARCINOGENESIS (stochastic) | Most important late somatic effect. |
| CATARACTOGENESIS (late tissue reaction) | Opacity of the lens of the eye. |
| EMBRYOLOGIC EFFECTS (stochastic) | - Birth defects. - Dependent on the embryonic stage of development. |
| _____________ is the most important late somatic effect. | Cancer. |
| Cataracts | - Opacity of the eye lens. - 2 Gy results in a partial or complete loss of vision. |
| Radiation induced cancer may take ____ or more years to develop. | 5. |
| Embryologic | - Birth defects. - All life forms most vulnerable during embryonic stage of development. - Period of gestation of exposure governs the effects-death or congenital abnormality. - Fetal radiosensitivity decreases as gestation progresses. |
| Carcinogenesis | - Cancer is the most important late stochastic effect caused by exposure to ionizing radiation. - This effect is a random occurrence that does not seem to have a threshold and for which the severity of the disease is not dose-related. |
| Radium Watch-Dial Painters | - 1920s and 1930s. - Development of osteoporosis and osteogenic sarcoma (bone cancer). |
| 1.Radiation-Induced Cancer | - Cancer caused by low-level radiation is difficult to identify. - Human evidence of radiation carcinogenesis comes from epidemiologic studies conducted many years after subjects were exposed to high doses of ionizing radiation. |
| 2.Radiation-Induced Cancer | - May take 5 or more years to develop in humans. - The physical appearance of cancer induced by ionizing radiation does not appear different than a cancer caused by other agents. |
| 3.Radiation-Induced Cancer | - Laboratory experiments with animals and statistical studies of human populations exposed to ionizing radiation prove that radiation induces cancer. |
| Early Medical Radiation Workers | Short term effects: - Cancerous skin lesions. Long term effects:: - Aplastic anemia. - leukemia. |
| Uranium Miners | One of the byproducts of uranium after it radioactively decays is titanium and molybdenum. |
| Patients injected with Thorotrast | - 1925-1945. - Used as a contrast agent. - Patients developed liver tumors. |
| Infants treated with radiation to reduce enlarged thymus gland | - 1940s and 1950s. - Thymus gland responds to infection by enlarging. - Treated by therapeutic doses of radiation. - Thyroid gland is in close proximity. - 20 years after treatment patients developed thyroid cancers. |
| Children of Marshall Islanders | - Exposed to high levels of fall out of atomic bomb test in 1954. - Thyroid cancer in these individuals has been observed. |
| Japanese Atomic Bomb Survivors | - August 6, 1945 the US dropped 1st atomic bomb on Hiroshima Japan marking a pivotal moment in World War II. - 3 days later another bomb was releasd on Nagasaki. - 88,000 killed. - 70,000 injured. |
| Patients with benign postpartum mastitis | - Given radiation therapy treatments to relieve symptoms. - Continued follow up on these patients. |
| Survivors of Atomic Bomb | - 1950 to 1956 117 new cases of leukemia were reported. - Solid tumors take 10 years to develop, so increases are being followed up. - 4:1 to 10:1 risk of getting breast cancer for Japanese women. |
| Survivors of Atomic Bomb: | - Every 300 atomic bomb survivors one died of a malignancy. - Directly related to magnitude of dose. - Plutonium and gamma. |
| Chernobyl Nuclear Disaster | - In 1986 a Nuclear Disaster in the City of Chernobyl resulting from a faulty nuclear power station. - The city of Pripyat, 2 miles from the plant sustained the majority of the effects. - 49,360 people were in the city at the time. |
| Other studies involving ionizing radiation: | Life span shortening: - Human studies. - Animal studies. |
| Cataract | A thickening of the lens of the eye. |
| B= | Normal eye. |
| A= | Eye with cataract. |
| Cataractogenesis | -There is a high probability that with only 2 Gyt will induce cataracts to form on the eye. -The chances of a single does of radiation to induce cataract formation is low. |
| Cataractogenesis: | -Fluoroscopic procedures do result in higher doses of radiation and therefore radiographers should use protective measures when in high level does of fluoro such as intervential procedures. |
| Genetic Effects | - Biological effects of ionizing radiation on future generations. - Also called Hereditary effects. |
| Mutagens | Agents involved in creating natural spontaneous mutation: - Elevated temperatures. - Chemicals. - Viruses. - Ionizing radiation. |
| Mutations caused by nature, no radiation involved: | - Hemophilia. - Huntington's chorea. - Downs syndrome. - Sickle cell anemia. - Cystic fibrosis. - Hydrocephalus. |
| Radiation induced mutations | - When exposed to ionizing radiation, mutations may occur. - Damage may be repaired before birth or may cause permanent birth defect. |
| Doubling Dose Concept | - Is the radiation dose that causes the number of spontaneous mutations occurring in a given generation to increase to two times their original number. |
| Doubling Dose Concept: | - The radiation doubling equivalent dose for humans, as determined from studies of the children of the atomic bomb survivors of Hiroshima and Nagasaki, is estimated to have a mean value of 1.56 Sv. |
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