Biology And safety Flashcards
SI unit of radioactivity
Becquerel (Bq)
1 Bq = 2.7 x 10^-11
Radioactivity
The measurement of decay rate or a radioactive material
Exposure
Measure of radioactive KINETIC ENERGY emitted from a source and is quantified a generally by its capacity to ionize air
SI units of exposure
Coulombs/kg
1 C/kg = 3876 R (roentgen)
Absorbed dose
The energy absorbed by any type of matter and is derived by calculating the imparted energy divided by the mass absorbing it
SI unit or absorbed dose
Gray
1 gray = 100 rad
Equivalent dose
Used to compare the biological effect on a tissue for different types of radiation
DEPENDENT ON LINEAR ENERGY TRANSFER
SI unit of equivalent dose
Sievert
1 sievert = 100 rem
Linear energy transfer
The rate at which energy is transferred from the ionizing radiation to soft tissue.
Used to determine equivalent dose
Effective dose
Used to measure the estimated risk to humans
- deleterious effect
- radio sensitivity of different tissues
Tissues with a higher effective dose show more affects to the same level of dose. More radio sensitive.
SI unit for effective dose
Sievert
Greater the number of effective dose
The greater the risk to that position of the human body
What tissues have the highest effective dose factor?
Bone marrow Breast tissue Stomach Colon Lung
Radiobiology
The study of ionizing radiation effects on living systems
Direct effect
When a photon or secondary electron ionizes biological macromolecules.
Photon + RH –> R* + H*
What are free radicals fates? (2)
Dissociation: R* –> X + Y *
Cross linking: R* + S* –> RS
Altered molecules differ structurally and functionally from originals
Radiolysis of water
Photon absorbed by water.
H2O + photon –> H* + OH*
In the presence of O2…
Produce hydrogen peroxide
Is hydrogen peroxide damaging?
YES! It is cytotoxic to the cell
Ionization of water leads to …
Free radical production
Indirect effect
The radicals produced by water radiolysis interacting with biological macromolecules
What are a radicals?
Unstable molecule with an unpaired electron. Will react with anything to become stable. Damaging to the cell and DNA
How much does the direct effect account for in biological adage from X-rays ?
1/3
How much does indirect effects account for in biological damage?
2/3
What is the primary cause of radiation induced cell death?
Damage to DNA
Damaged DNA results from: (4)
Breakage of one or both DNA strands
Cross linking DNA
change or loss of base
Disruption of hydrogen bonds between DNA strands
Deterministic Effect
Radiation injury is DEPENDENT on the dose
Requires higher level of exposure
There IS an exposure threshold
Generally tissue related
What is a exposure threshold
The amount of exposure required to have an effect occur which is clinically observable
Below the threshold - there is no effect, no clinical observations
Short term deterministic effects are seen primarily where?
Seen in it issues that have rapidly dividing and many undifferentiated stem cells
Bone marrow, GI tract, oral mucous
Long term deterministic effects
Loss of parenchymal cells - replaced by fibrous connective tissues
Loss of capillaries
Loss of capillaries results in (3) impaired…
Oxygen transport
Nutrient transfer
Waste removal
What factors can you modify to reduce deterministic effects? (4)
Dose
Dose rate
Oxygen
LET
What type of cells have high sensitivity to radiology?
Cells that…
Divide regularly
Long mitotic futures
Undergo little or no differentiation
BONE MARROW
MUCOUS MEMBRANES
SEX ORGANS
Cells that have low sensitivity to radiology ?
Cells that …
Are highly differentiated
Incapable of division
MUSCLE
EYE
List oral manifestations of irradiation? (6)
Lose of taste Mucositis Xerostomia Radiation caries Trismus Osteoradionecrosis
What is the stochastic effect?
Radiation injury based on PROBABILITY of occurrence
“All or nothing”
Probability increases with dose
NO threshold
– there is no level of exposure at which there is 0 risk —
How do stochastic effects damage?
Sublethal damage to DNA
Induced cancers and genetic alterations
Greater dose = greater or lesser stochastic damage?
Greater
What is the average natural effective dose of radiation does someone get per year?
2.4 micro sievert
What is the average effective does an individual gets from man made radiation?
2.5 micro sievert
How much does do you get from one dental X-ray?
.005 millisievert
Comparable to one day of natural exposure
1400 dental X-rays = 240 five hour flights = 19 years of smoking a pack of cigarettes a day
.
What dental X-ray has the highest dose?
Panoramic
-except a full mouth set with digital X-ray
What is the probability of getting a long term risk from a pano?
One in a million
What are the three guiding principles in radiation safety?
Justification
ALARA
Dose limitation
Justification
Selecting radiographs that benefit the patient
The dentist has an obligation to do more good than harm
ALARA
As low as reasonably achievable
Keep radiation exposures to a minimum for adequate diagnosis and evaluation
Dose limits
There are no dose limits in diagnostic and therapeutic radiology
Should dentists prescribe routine X-rays at preset intervals?
No
Prescribe radiographs pertaining to a patients needs. If a high caries risk pt you might want to take radiographs every six months
What type of film speed should be used that requires less radiation?
High speed
E or F
What type of film speed is slow
D
Does digital imaging require more or less radiation?
Less
What are intensifying screens?
Contain rare earth elements that give off light photons when struck by X-rays.
These light photons strike the underlying film. Requires less radiation
Longer source to skin reduces exposure. T or F
True
Rectangular collimators do not focus the beam to an area. Therefore do not reduce the exposure. T or F
False - they reduce exposure and focus the beam
How does filtration of the X-ray beam work?
Aluminum filter removes low energy photons
How far for the radiation source should you stand?
2 meters or 6 feet
Radiation exposure decreases inversely or directly to the square of the distance
Inversely
Where should the operator be positioned in relation to the he primary X-ray beam?
90-135 degrees
How often do you need to inspect the X-ray unit?
Every 5 years
Ionizing radiation is…
Radiation is sufficient energy to displace atomic electrons thus breaking bonds that hold a molecule together.
Produces molecular changes
What are three types of ionizing radiation?
X-rays
Gamma rays
UV light
What is the number one natural source of radiation?
Radon
What is the number one source of man made radiation?
CT scans
Name the two types of ionizing radiation:
Particular radiation
Electromagnetic radiation
What does particulate radiation consist of?
Alpha
Beta
Neutrons
What does elctromagnetic radiation consist of?
Gamma and x rays
Radiation
Transmission of energy through space and matter
What can ionizing radiation lead to in living cells?
Cell death
Molecular alteration leading to harmful affects
