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88 Cards in this Set
- Front
- Back
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Mechanisms of Injury |
x-rays that do not reach the dental x-ray film; and are absorbed by the patient’s tissue |
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Two mechanisms of radiation injury |
IonizationFree radical formation |
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When x-rays are absorbed by the patient’s tissue |
Chemical changes occur that result in biologic damage. |
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Radiation Injury |
All ionizing radiations are harmful and produce biological changes in living tissues |
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Ionization |
Results when x-rays strike patient tissue Results in formation of a positive atom and dislodged negative electron |
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With ionization, the ______ will interact with other _____ within the ________ tissues causing chemical changes within the cell that results in ________ damage |
electron, atoms, absorbing, biologic |
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Free Radical Formation |
Cell damage occurs primarily through formation of free radicals |
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When are free radicals formed |
when an x-ray photon ionizes water/primary component of living cells |
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A free radical is |
Highly reactive and unstable |
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Damage to living tissue caused by exposure to ionizing radiation may result from |
A direct hit and absorption of an x-ray photon within a cell Absorption of an x-ray photon by water within a cell |
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Two theories of Radiation Injury |
Direct theory Indirect theory |
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Direct Theory |
Cell damage results when ionizing radiation directly hits critical areas within the cell. This occurs infrequently Direct strike of DNA |
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Most x-ray photons pas through cell and cause |
little damage |
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Indirect Theory |
X-ray photons are absorbed within the cell and cause the formation of toxins, which in turn damage the cell. |
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When x-ray photons are absorbed by water within a cell what is the result |
free radical formation results. |
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Cells are what percentage of water |
70%-80% |
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The free radicals combine to form |
toxins that damage cells Cause cell dysfunction & biological damage |
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If all ionizing radiations are harmful and produce biologic damage, what level of exposure is considered acceptable? |
None |
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Dose-Response Curve |
Dose and damage are plotted on a graph, a linear non-threshold relationship is seen. Correlate the damage of tissue with the dose of radiation received. |
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Non-threshold Relationship |
Indicates that a threshold dose level for damage does not exist Suggests that no matter how small the amount of radiation received, some biological damage does occur No SAFE amount of radiation |
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Stochastic Effects |
* direct function of dose * Show up years after exposure * not certain that cancer or genetic damage will result. No dose threshold; effects do not depend on the magnitude of the absorbed dose Examples - cancer and genetic mutations |
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As dose of radiation -------------, probability that cancer or genetic effect will occur ------------ |
increases, increases |
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Non-stochastic Radiation Effects |
Somatic effects that have a threshold and increase in severity with increasing absorbed dose Cause and effect relationship between radiation and some side-effects Require larger radiation doses to cause serious impairment of health |
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Examples of Non-stochastic Radiation Effects |
erythema, loss of hair, cataracts, and decreased fertility |
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Sequence of Radiation Injury |
Latent period Period of injury Recovery period Cumulative effects |
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Period of injury |
A variety of cellular injuries may result |
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Latent period |
The time that elapses between exposure to ionizing radiation and the appearance of clinical signs Depends on the total dose of radiation received and the amount of time it took to receive the dose |
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Cumulative effects |
Effects of radiation exposure are additive. Unrepaired damage accumulates in tissues. |
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Recovery period |
Depending on a number of factors, cells MAY repair the damage caused by radiation. |
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Determining Factors for Radiation Injury |
Total dose Dose rate Amount of tissue irradiated Cell sensitivity Age |
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Total dose |
total amount of radiation absorbed |
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Dose rate |
rate at which exposure occurs |
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Amount of tissue irradiated |
total-body more effects than small areas |
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Cell sensitivity |
rapid dividing cells more sensitive |
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Age |
children more sensitive than adults |
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Short-term effects |
Associated with large doses of radiation in a short amount of time |
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Acute radiation syndrome (ARS) |
Includes nausea, vomiting, diarrhea, hair loss, hemorrhage |
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Long-term effects |
Small doses absorbed repeatedly over a long period of time Effects seen after years, decades, or generationsCancer, birth abnormalities, genetic defects |
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Somatic cells |
All cells in the body except the reproductive cells Seen in the person irradiatedNot seen in future generations |
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Genetic cells |
The reproductive cells Not seen in the person irradiatedPassed on to future generations |
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Biologic effects of radiation can be classified as |
somatic or genetic. |
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radiosensitive |
A cell that is sensitive to radiation is termed |
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radioresistant |
one that is resistant is termed |
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Radiation Effects on Cells |
radioresistant radiosensitive The response is determined byMitotic activity Cell differentiation Cell metabolism |
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Radiosensitive organs |
Lymphoid tissueBone marrowTestesIntestines |
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Radioresistant tissues |
Salivary glands Kidney Liver |
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Critical organ |
An organ that, if damaged, diminishes the quality of a person’s life |
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Critical organs exposed during dental radiographic procedures include |
Skin Thyroid gland Lens of the eye Bone marrow |
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Tissue or Organ: bone marrow |
Radiation effect: Leukemia
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Tissue or Organ: reproductive cells |
Radiation effects: genetic mutations |
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Tissue or Organ: salivary gland |
radiation effects: carcinoma |
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Tissue or Organ: Thyroid |
radiation effects: carcinoma |
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Tissue or Organ: skin |
Radiation effects: carcinoma |
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Tissue or Organ: lens of the eye |
radiation effects: cataracts |
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Radiation Measurement Topics: Units of Measurement |
Exposure measurement Dose measurement Dose equivalent measurement |
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Units of Measurement |
Time=minutes Distance=miles or kilometers Weight=pounds/kg Dental radiation=R, rad,rem |
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Traditional (older) units of radiation measurement |
Roentgen (R)Radiation absorbed dose (rad)Roentgen equivalent (in) man (rem) |
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SI (newer) units of radiation measurement |
Coulombs/kilogram (C/kg) Gray (Gy) Sievert (Sv) |
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Exposure Measurement |
Measurement of ionization in the air produced by x-rays Roentgen ®-traditional unit of exposure for x-rays “The quantity of x-radiation that produces an electrical charge of 2.58x10-4 coulombs in a kg of air at standard temperature”. |
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Roentgen ® |
Measure ® Volume of air is irradiated Ionization occurs Electrical charges are collected and measured **measures amount of energy that reaches the surface of an organism-not radiation absorbed |
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Dose Measurement (rad) |
Dose-amount of energy absorbed by a tissue Using SI units 1 rad=0.01 joule per kilogram |
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Dose Measurement Rad |
The amount of energy absorbed by tissue |
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radiation absorbed dose (Rad) |
A special unit of absorbed dose that is equal to the deposition of 100 ergs per gram of tissue. *Can be applied to all forms of radiation. Not restricted to air. *Applies to EVERY type of tissue |
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Dose Equivalent Measurement (rem) |
Different types of radiation have different effects of tissues |
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Dose equivalent measurement is used to |
compare bio effects of different types of radiation |
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Dose equivalent (or effective dose) combines the amount of radiation absorbed |
amount of radiation absorbed and the medical effects of that type of radiation. |
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Dose Equivalent Measurement (rem) |
j |
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Sources of Radiation Exposure |
*Natural background radiation * Artificial or man-made radiation |
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Artificial or man-made radiation |
Resulting from modern technology |
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Natural background radiation |
A form of ionizing radiation that is ubiquitous in the environment Cosmic radiation: Stars and sun Terrestrial radiation :Radioactive materials in the earth and air |
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In the United States the average dose of background radiation received by an individual ranges from |
150 to 300 mrads per year. |
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The potential risk of dental radiography inducing a fatal cancer in an individual has been estimated to be |
3 in 1 million. |
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The risk of a person developing a cancer spontaneously is much higher, or 3300 in 1 million. |
much higher, or 3300 in 1 million |
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Risk and Risk Estimates |
1 in a million risks of a fatal outcome |
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What is the estimated dose necessary to produce cancer in thyroid gland |
6000 mrads |
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what is the Average dental dose necessary to induce thyroid cancer |
is only 1/1000 of dose |
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Areas of maxilla and mandible exposed during dental radiography account for __________ percent of active bone marrow |
very small |
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Risk of cancer induced (leukemia) is directly associated |
with amount of blood-producing tissues irradiated and the dose |
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Leukemia is included by doses of |
5000 mrads or more |
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Average dental mrads is |
1-3 mrads |
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Total of 250 rads in a 14-day period causes |
erythema, reddening of skin More than 500 dental films in a 14-day period would have to be exposed. |
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How many mrads are necessary to induce cataract formation? |
More than 200,000 meads Some scientists consider eyes no longer a critical organ |
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Film Speed |
*Use fastest film possible (F-speed) *Reduces absorbed dose by 60% *Using F-speed film instead of E-speed film reduces absorbed dose by additional 20% |
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Collimation |
*Radiation exposure limited by using rectangular collimation *Rectangular collimation reduces absorbed dose by 60%-70% |
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Technique |
Exposure limited by increasing source-to-film distance |
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Use long-cone paralleling technique and increased source-to-film distance reduces |
skin dose |
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Exposure Factors |
Radiation exposure can be limited by using a higher kVp Reduces skin dose |
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Dental radiographs should be prescribed for a patient only when |
the benefit of disease detection outweighs the risk of biologic damage |
