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35 Cards in this Set
- Front
- Back
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Radiation Biology |
•Thestudy of the effect of ionizing radiation on living tissue
•Facilitatesbetter understanding of the harmful effects of radiation •Allradiations are harmful and produce biological changes in living tissues •Notall x-rays pass through the client and reach dental x-ray film. •Somerays are absorbed by client tissues •Chemicalchanges occur that result in biological damage. |
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IONIZATION
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•X-raysare a form of ionizing radiation.
•Whenx-rays strike a client, ionization results. •Chemicalchanges occur within the cell thus causing biological damage. •Ionizationis produced through photoelectric effect or Compton Scatter. •Resultsin the formation of a positive atom and a dislodged negative electron •Electroninteracts with other atoms giving off kinetic energy and causing furtherionization. |
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FREERADICAL FORMATION
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•Primarymeans by which x-radiation causes cell damage.
•Occurswhen an x-ray photon ionizes water (primary component of living cells) •Water Ionization = hydrogen + hydroxyl free radicals. |
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FREE RADICALS |
•Uncharged(neutral) atoms or molecules that exists with single, unpaired electron in itsoutermost orbit (shell)
•Itpossess characteristics of unstability andhigh reactivity •Itwill bind and recombine to regain stability•Believedto be involved in degenerative diseases and cancers. |
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DIRECT THEORY |
•There is evidence of cell damage as aresult of ionizing radiation targeting critical areas. Ex: x-ray photon directly striking DNAcell causing injury to irradiated organism.
•Occurs infrequently.
•Most x-ray photons pass through the celland cause little or no damage |
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INDIRECT THEORY |
•X-ray photons are absorbed within cellcausing toxins thusdamaging the cell
•Free radicals combine to form toxinscausing cellular dysfunction and biological injury. •Damage is not a result of a direct “hit”by x-ray photons•Occurs frequently because of the highwater content in the cells (70 – 80% water) |
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DOSE-RESPONSECURVE�
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•Correlates the response anddamage of tissues with the dose oramount of radiation received.
•In dental radiography, although the dosesreceived by the patient are low, damage does occur. •There is no safe amount of radiationexposure. |
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DOSE-RESPONSE CURVE &RADIATION INJURY
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THRESHOLDCURVE Indicatesthat below a certain level (threshold), no response is evident
LINEARCURVE Indicatesthat the response is proportional to the dose. LINEARNON-THRESHOLD CURVE Indicatesthat a response is seen at any dose |
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STOCHASTIC
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Randomlydetermined; having a random probability distribution or pattern that may beanalyzed statistically but may not be predicted precisely.
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STOCHASTIC EFFECTS
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•Occuras a direct function of dose
•Severityof effects is not dependent on the magnitude of the absorbed dose •Doesnot posses a dose threshold •Dueto effect of ionizing radiation on chromosomes•Ex:cancer (tumor) |
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NONSTOCHASTICEFFECTS
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•Somatic effects that have a threshold.
•Increase in severity as absorbed doseincreases. •Caused by significant cell damage – thenphysical effects occur•Ex: erythema, loss of hair, cataractformation, infertility |
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LATENT PERIOD |
•The time that elapses between exposureand observable clinical signs
•The more radiation received, the fasterthe dose rate and thus the shorter thelatent period |
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INJURY PERIOD |
•Follows the latent period
•Cellular damage may result eg:cell necrosis, cell transformations etc. |
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RECOVERY PERIOD |
•Notall cellular radiation injuries are permanent
•Cellularrepair follows cellular damage •Mostof the damage caused by low-level radiation is repaired within the cells of thebody. •Radiationeffects are cumulative: damage that remains unrepairedaccumulates in the tissues. •Cumulativeradiation effects include: cancer, cataract formation, birth defects3dd;this.left\u003de};_.k\u003d_.Vi.prototype;_.k.getHeight\u003dfunction(){return this.bottom-this.top |
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RADIATION INJURY |
Total dose Dose Rate Area exposed Cell sensitivity Age |
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TOTAL DOSE |
•Refers to the quantity of radiationreceived, or the total amount of radiation energy absorbed.
•MORE DAMAGE OCCURS WHEN LARGEQUANTITIES OF RADIATION ARE ABSORBED BY A TISSUE |
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DOSE RATE |
•Refersto rate at which exposure to radiation occurs and absorption takes place
•Moreradiation damage occurs because of higher dosage rates – the cells need time toheal themselves!
Geneticand somatic cells make up tissues of human body |
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GENETIC CELLS |
•ReproductiveCells (ova, sperm)
•Undergocell mutation ie: cannot repair themselves •Notseen in the individual who is irradiated but rather in future offspring |
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SOMATIC CELLS |
•Consistof all other cells other than reproductive•Ex:cells of skin, hair, blood, glands, bone, nerves, muscles
•Donot undergo cell mutation ie:are able to heal themselves up to a certain point•Agiven dose of radiation is less dangerous ifadministered in two smaller doses than onelarger one •Allowingtime to elapse between doses allows somatic cells to repair themselves•Effectsinclude cancer, leukemia, cataracts |
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AREA EXPOSED |
•The larger the area exposed (irradiated),the greater the injury to the individual
•Damage occurs to the blood-formingtissues |
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CELL SENSITIVITY |
•More damage occurs in cells that are mostsensitive to radiation ex: young cells
RADIOSENSITIVE A cell sensitive to radiation ex: smalllymphocyte, bone marrow, reproductive RADIORESISTANT A cell resistant to radiation ex: muscle,nerve, mature bone |
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ACUTE DOSE OF BLOOD CELLS |
•Internal bleeding
•Fatigue •Bacterial infections •Fever |
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ACUTE DOSE OF GASTROINTESTINAL CELLS |
•Nausea
•Vomiting •Diarrhea •Dehydration •Bleeding ulcers |
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ACUTE DOSE OF NERVE CELLS
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•Loss of co-ordination
•Coma •Confusion •Shock •Convulsions |
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Who are more susceptible to radiation injury ?
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Children and ederly |
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SHORT TERM EFFECTS |
•Effects are seen within minutes, days, orweeks following latent period
•Large amounts of radiation in a shortperiod of time •Do not apply to Dentistry |
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SMALL TERM EFFECTS |
•Small amounts of radiation absorbedrepeatedly over a long period of time
•Apply to Dentistry |
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BACKGROUND RADIATION
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•Naturally occuringbackground radiation includes cosmic and terrestrial radiation.
•Cosmic radiation originates from thestars and sun.
•Terrestrial radiation is emitted fromradioactive materials present in the earth and air ex: potassium, uranium |
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NEW SYSTEMSysteme Internationale (SI)
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•Coulombs/Kilogram (C/kg)
•Gray (Gy) •Sievert (Sv) |
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OLD SYSTEMTraditional / Standard
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•Roentgen (R) - exposure
•Radiation Absorbed Dose (rad) •Radiation Equivalent (in) Man (rem) |
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ROENTGEN (COULOMB) radiation /exposure
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•Theroentgen measures the energy produced by gamma radiation in a cubic centimeterof air. - measuresradiation exposure
•It isusually abbreviated with the capital letter "R". •A milliroentgen, or"mR",is equal to one one-thousandth of a roentgen. •Anexposure of 50 roentgens would be written "50 R". |
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RAD (GRAY)
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•RadiationAbsorbed Dose recognizes that different materials thatreceive the same exposure may not absorb the same amount of energy - amount ofenergy absorbed by a tissue••A radmeasures the amount of radiation energy transferred to some mass of material,typically humans. ••Oneroentgen of gamma radiation exposure results in about one rad ofabsorbed dose.
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REM (SIEVERT)
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•RoentgenEquivalent Man (rem) is aunit that relates the dose of any radiation to the biological effect of thatdose. – different types of radiation have different effects on tissues. •Torelate the absorbed dose of specific types of radiation to their biologicaleffect, a "quality factor" must be multiplied by the dose in rad,which then shows the dose in rems.
•Forgamma rays and beta particles, 1 rad ofexposure results in 1 rem of dose |
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IN DENTAL RADIOGRAPHY, THE CRITICAL ORGANS AT RISK INCLUDE
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1. THYROID GLAND
2. BONE MARROW 3. SKIN 4. EYES |
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QUANTITYOF EXPOSURE VARIES DEPENDS ON:
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1. FILM SPEED F-speed film instead of D-speed film.
2. COLLIMATION•Rectangularinstead of round collimation reduces absorbed dose by 60 – 70% 3. TECHNIQUE Longcone paralleling technique and longer target-to-film distance reduces skindose. 4. EXPOSURE HigherkVpreduces skin dose……why? •Less exposure time |
