LO 4 Flashcards
All _______ radiations are harmful and cause _________
Ionizing; biologic changes in living tissue
Although the amount of x-radiation used in dental radiography is small
biologic damage does occur
What are the 2 mechanisms of radiation injury?
- Ionization
- Free radical formation
Describe ionization in relation to radiation
- Results when x-ray strikes patient’s tissue
- Produced through photoelectric effect or Compton scatter
- Results in formation of positive atom and dislodged electron
- Electron interacts with other atoms within absorbing tissue - chemical change in cell = damage
- Can have little effect if sensitive molecules not altered or can have profound effect on cell function (e.g. DNA)
X-radiation causes cell damage primarily through the formation of ________
Free radicals
What causes free radicals to form?
- X-ray photon ionizes water, the primary component of a living cell
- Results in the production of hydroxyl and hydrogen free radicals
- They are highly reactive and unstable
What 3 things may free radicals do to achieve stability?
- Recombine without causing changes in the molecule
- Combine with other free radicals and cause changes
- Combine with ordinary molecules to form a toxin (hydrogen peroxide H2O2) capable of producing wide spread cellular changes
What 2 theories describe how radiation damages biologic tissue?
- Direct theory
- Indirect theory
What is the direct theory of biologic damage?
- Cell damage results when ionizing radiation directly hits critical areas within a cell
- Occurs infrequently
- Most x-ray photons pass through the cell and cause little to no damage
What is the indirect theory of biologic damage?
- X-ray photons absorbed withing cell and cause formation of toxins, which in turn damage the cell
- When x-ray photons are absorbed by water in the cell, they form free radicals
- Free radicals combine to form H2O2
What is a dose response curve?
Correlates/plots the response/damage of tissue with the dose or amount of radiation recieved
What does it mean that when dose and damage of radiation are plotted a linear, nonthreshold relationship is seen?
- Leanear indicated response of tissue is directly proportional to dose
- Nonthreshold means there is no certain level where damage does not exist - it starts immediately
Describe stochastic radiation effects
- It’s a direct function of the dose
- PROBABILITY of occurrence increases with dose, but SEVERITY is not dependent on the magnitude of absorbed dose
- No dose threshold
- Examples are cancer and genetic mutations
Describe nonstochastic radiation effects
- These are somatic effects that have a threshold - they DO increase in severity with absorbed dose
- Require larger radiation doses to cause serious health impacts
- E.g. erythema, hair loss cataracts, decreased fertility
What is the sequence of radiation injury?
- Chemical reactions (ionization/free radical formation) happen rapidly - observable effects not visible immediately after exposure
- A latent period elapses between exposure of ionizing radiation and observable clinical signs
- After the latent period, a period of injury occurs
- Recover period begins - not all injuries are permanent, but each exposure causes cellular damage which is followed by repair
The more radiation recieved and the faster the dose rate, the _______ the latent period
Shorter
What types of cellular injuries may occur as a result of radiation exposure?
- Cell death
- Changes in cell function
- Breaking or clumping of chromosomes
- Abnormal mitotic activity
Most damage caused by low-level radiation is _________
Repaired within the cells of the body
Unrepaired damage ______ in the tissues and this can lead to ______ after repeated exposures
Accumulates; health problems
Define recovery period
Depending on a number of factors, cells can repair the damage caused by radiation
Define cumulative effects
- The effects of radiation are additive
- Unrepaired damage accumulates in tissue
What are the 5 determining factors of radiation injury?
- Total dose - quantity of radiation recieved or total amount of radiation absorbed
- Dose rate - rate at which exposure to radiation occurs. Dose rate = dose/time
- Amount of tissue irradiated - total body irradiation causes more damage than localized
- Cell sensitivity - more damage occurs in cells that are sensitive to radiation (rapidly dividing or young cells)
- Age - children are more susceptible than adults
What are the short-term effect of radiation?
- Seen within minutes, days, or weeks
- Associated with large amounts of radiation in a short time (nuclear accident - NOT dentistry)
What are the long-term effects of radiation?
- Appear over years, decades, or generations
- Small amounts absorbed repeatedly over a long period
What are the somatic and genetic effects of radiation?
- Somatic cells - all cells in body except reproductive, seen in the person irradiated
- Genetic cells - reproductive cells, passed on to future generations
A cell that is sensitive to radiation is termed _________ while those that are resistant are termed ________
Radiosensitive; radioresistent
The response of cells to radiation is determined by _______
- Mitotic activity
- Cell differentiation (has it specialized yet?)
- Cell metabolism
Is the majority of radiation we recieve on a day-to-day basis natural or man-made?
Man-made
What is a critical organ?
An organ that, if damaged, diminishes the quality of a person’s life
Critical organs exposed during dental radiogrpahic procedures include _______
- Skin
- Thyroid gland
- Bone marrow
- Lens of eye
(Also oral mucosa and salivary gland)
What are the 3 units of radiation measured?
- Exposure
- Dose
- Dose equivalent
The two measurement systems used are ________
- Standard system (older)
- SI system/systeme international
What is the most important unit of radiation measurement in the standard system?
Radiation absorbed dose (rad)
What is the most important unit of radiation measurement in the SI system?
Sievert (Sv)
What is the SI equivalent to the rad (radiation absorbed dose)?
The gray (1Gy = 100 rads)
What do sieverts measure?
Compares the biologic effects of different kinds of radiation
What is the standard system equivalent to the sievert?
Roentgen equivalent man (1Sv = 100 rems)
What does the radiation absorbed dose measure?
The amount of energy absorbed by tissue
What is natural background radiation?
- A form of ionizing radiation that is everywhere in the environment (cosmic radiation - stars and terrestrial radiation - earth and air)
- Average dose in U.S. is 150 - 300 mrads per year
What is artificial/human-made radiation?
- Results from modern technology (consumer products, atomic fallout, weapons production, nuclear fuel cycle)
- Includes medical radiation (dental radiography, medical radiogrpahic procedures, radiation therapy, etc)
The risk of dental radiography inducing camera in an individual is estimated to be ______ while the risk of developing it spontaneously is _____
- 3 in 1 million
- 3300 in 1 million
The amount of exposure a client recieved from dental radiographs depends on _______
- Film speed
- Collimation
- Technique
- Exposure factors
Dental radiographs should only be prescribed for a patient when _______
The benefit of disease detection outweighs the risk of biologic damage
