DENT 1050 Test #1, Chapters 4 and 5 Flashcards
Radiation injury; All radiation is:
harmful and produces biologic changes in living tissue
Radiation injury; Free radical formation:
i. Primary form of damage x-radiation causes
ii. Occurs when an x-ray ionizes water
1. Results in hydrogen and hydroxyl free radicals
Free radical
an uncharged (neutral) atom or molecule that exists w/a single, unpaired electron in its outermost shell; highly reactive and unstable
To achieve stability, free radicals do 1 or 3 things:
a. Recombine w/o causing changes in the molecule
b. Combine w/ other free radicals and cause changes
c. Combine w/ ordinary molecules to form a toxin - damaging
Direct Theory of radiation injury
Cell damage results when ionizing radiation directly hits critical areas within the cell (DNA) - occurs infrequently
Indirect Theory of radiation injury
X-ray photons are absorbed w/in the cell and cause the formation of toxins which in turn damage the cell via free radicals;
i. greater chance of free radical formation because cells are 70-80% water
ii. actual damage done is BY the free radicals, ions and toxins, NOT the actual x-ray
Dose-Response Curve
used to correlate the “response” or damage of tissues w/the dose or amount of radiation received
Linear relationship of dose-response curve
response of the tissues - damage - is directly proportional to the dose
Nonthreshold relationship of dose-response curve
a threshold dose level for damage doesn’t exist; do not need a certain dose for damage to occur; NO absolute SAFE amount of radiation exposure
Radiation Injury Sequence, Repair & Accumulation
Latent period, period of injury, recovery period, cumulative effects
Latent Period of radiation injury
the time that elapses between exposure to ionizing radiation and the appearance of observable clinical signs; the more radiation received and the faster the dose rate -> the shorter the latent period
Period of injury of radiation injury
follows the latent period when cells show damage
Recovery period of radiation injury
depending on a number of factors, cells can repair the damage caused by radiation (if allowed time to repair)
Cumulative effects of radiation injury
the effects of radiation exposure are additive and damage that remains unrepaired accumulates in the tissue
Determining factors for radiation injury
Total dose, dose rate, amount of tissue irradiated, cell sensitivity, age
Determining factors: Total dose
quantity of radiation received
Determining factors: Dose rate
dose/time; more damage takes place with high dose rates b/c a rapid delivery of radiation doesn’t allow time for the cellular damage to be repaired
Determining factors: Amount of tissue irradiated
extensive radiation injury occurs when large areas of the body are exposed because of the damage that occurs to the blood-forming tissues (nuclear energy disaster)
Determining factors: Cell sensitivity
rapidly dividing, young cells are more adversely affected
Determining factors: Age
children are more susceptible to radiation damage than adults
Radiation effects: Short-term
a. seen within minutes, days or weeks
b. large amounts of radiation absorbed in a short amount of time
c. Acute Radiation Syndrome (ARS)
d. rarely seen in dentistry
Acute Radiation Syndrome (ARS)
includes nausea, vomiting, diarrhea, hair loss, hemorrhage
Radiation effects: Long-term
a. appear after years, decades or generations
b. Associated w/small amounts of radiation absorbed repeatedly over a long period of time
c. linked to induction of cancer, birth abnormalities and genetic defects
Radiation effects: Somatic effects, somatic cells
- ALL THE CELLS IN THE BODY EXCEPT REPRODUCTIVE CELLS
i. somatic effects; seen in the person irradiated
ii. cell changes are NOT transmitted to future generations
Radiation effects: Genetic effects, genetic cells
- REPRODUCTIVE CELLS: OVA & SPERM
i. genetic effects: NOT seen in the person irradiated, but are passed on to future generations
ii. genetic damage can NOT be repaired
Radiation effects on cells: Cancer cells
rapidly divide and are less differentiated - that’s why radiation therapy can be successful in the treatment of cancer
Radiation effects on tissues and organs: Critical organs
organ that if damaged diminishes the quality of a person’s life
i. critical organs exposed during dental radiographs: skin, thyroid, lens of the eye, bone marrow
Radiation measurements: Units of measurement
units are used to define: exposure, dose, dose equivalent; two systems: Traditional and Systeme Internationale
Radiation measurements: Traditional system
a. Roentgen (R)
b. Radiation absorbed dose (rad)
c. Roentgen equivalent (in) man (rem)
Radiation measurements: Systeme Internationale
*QF, quality factor; J, joule
a. Coulombs per kilogram (C/kg)
b. Gray (Gy)
c. Sievert (Sv)
Coulomb (C)
unit of electrical charge; the quantity of electrical charge transferred by 1 ampere in 1 second
Ampere (A)
unit of electrical current strength; current yielded by 1 volt against 1 ohm of resistance
Erg (erg)
unit of energy equivalent to 1.0 x 10^-7 joules or to 2.4 x 10^-8 calories
Joule (J)
SI unit of energy equivalent to the work done by the force of 1 newton acting over the distance of 1 meter
SI
International System of Units
Newton (N)
SI unit of force; the force that, when acting continuously on a mass of 1 kilogram, will impart to it an acceleration of 1 meter per second squared (m/sec^2)
Kilogram (kg)
Unit of mass equivalent to 1000 grams or 2.205 pounds
both Roentgen and Coulombs are measured in:
1 cc of air and 1 kg of air
Roentgen (R)
Definition: 1 R = 87 erg/g
Conversion: 1 R = 2.58 x 10^-10 C/kg
Radiation absorbed dose (rad)
Definition: 1 rad = 100 erg/g
Conversion: 1 rad = 0.01 Gy
Roentgen equivalent (in) man (rem)
Definition: 1 rem = rads x QF
Conversion: 1 rem = 0.01 Sv
*QF, quality factor
Coulombs per kilogram (C/kg)
Definition: —
Conversion: 1 C/kg = 3880 R
Gray (Gy)
- starred conversion
Definition: 1 Gy = 0.01 J/kg
Conversion: 1 Gy = 100 rads
Sievert (Sv)
- starred conversion
Definition: 1 Sv = Gy x QF
Conversion: 1 Sv = 100 rems
*QF, quality factor
Radiation risks: In the U.S. the average dose of background radiation (BR) per year is:
150-300 mrads
Radiation risks: risk and risk estimates
- Risk: likelihood of adverse effects or death resulting from exposure to a hazard
- Risk of dental radiography inducing a fatal cancer: approx. 3/1,000,000
- Risk of spontaneous cancer: 3,300/1,000,000
- Death is more likely to occur from common activities than from dental radiography
Radiation risks: dental radiation and exposure risks; Thyroid gland
estimated dose of 6,000 mrads is necessary to produce cancer - dental radio dose is usually 6 mrads
Radiation risks: dental radiation and exposure risks; Bone marrow
mand./max make up 1% of the body’s total bone marrow; Leukemia (directly associated with the amount of blood-producing tissues irradiated and the dose) is induced most likely at doses of 5,0000 mrads - avg bone marrow dose: 1-3 mrads from periapical
Radiation risks: dental radiation and exposure risks; Skin
250 rads in 14-day period causes erythema - would have to have more than 500 dental films in 14-day period
Radiation risks: dental radiation and exposure risks; Eyes
more than 200,000 mrads are necessary to induce cataracts - avg surface dose to cornea of the eye is approx. 60 mrads
Collimation
Definition: restriction of the size and shape of the x-ray beam in order to reduce patient exposure;
Reduces 60-70%
Risk vs Benefit of dental radiographs
the benefit of disease detection far outweighs the risk of damage from x-radiation
Patient protection: Pregnancy
i. the recommendations don’t have to be altered
ii. FMS (18 films) w/ lead apron receives 1 mrem to uterus
iii. Background radiation in 9 mo. receives 225 mrem to uterus
iv. avoid it unless absolutely necessary (weigh risk to benefit
Proper equipment: Filtration
added filtration: aluminum disks placed in the path of the x-ray between the collimator & the tubehead seal; used to filter out the longer wavelength, low-energy x-rays; added in 0.5 mm increments
Proper equipment: Position-Indicating Device (PID); which is more effective but what is its disadvantage
rectangular is more effective than the round at reducing patient exposure; disadvantage is that it’s easier to “cone”-cut
Thyroid collar
NOT recommended for use w/ extraoral films (panoramic) (results in non-diagnostic films - obscures information
Fast Film
Single most effective method in reducing a pt’s exposure to x-radiation
E-speed (Ektaspeed)
fastest intraoral film available; compared to D-speed film, it requires 1/2 exposure time
Operator protection
THE DENTAL RADIOGRAPHER MUST AVOID THE PRIMARY BEAM. Dental radiographer should stand at a position perpendicular to the primary beam (90-135 degrees)
Radiation exposure guidelines
Radiation Control for Health and Safety Act: enacted 1968
Consumer-Patient Radiation Health and Safety Act: enacted 1981
Maximum Accumulated Dose (MAD)
occupationally exposed workers must not exceed an accumulated lifetime radiation dose - dose can and should be “0”
Maximum Accumulated Dose (MAD)
determined by worker’s age (minimum age requirement is 18 years)
ALARA concept
all exposure to radiation must be kept to a minimum or “AS LOW AS REASONABLY ACHIEVABLE”
