Safety Flashcards
Define ionizing radiation
radiation that possesses the ability to remove electrons from atoms by a process called ionization
What are somatic effects?
effects of radiation that damages the cell itself
Define attenuation
the loss of intensity in an x-ray beam as it passes through matter.
What is the unit of exposure?
Air kerma or coulombs/kilogram (air kerma preferred)
What is the unit of absorbed dose?
Gray
energy absorption per kilogram of tissue irradiated
Joules per kilogram (1Gy= 1 J/kg)
Gyt is what unit of measurement?
Gray(tissue) = unit of radiation absorbed in tissue
Gya is what unit of measurement?
Gray(air) = unit of radiation absorbed in air
What is the unit of effective dose?
Sievert
Define effective dose
the relative risk to humans of exposure to ionizing radiation
Define equivalent dose
(occupational exposure) Product of absorbed dose times the radiation weighting factor
Define absorbed dose
Quantifies the biologic effects of radiation on humans and animals
What describes patient dose?
absorbed dose
What is the SI equivalent for RAD?
Gray (Gy)
What is the SI equivalent for Rem?
Sievert (Sv)
What is the SI unit for Roentgen (R)?
Coulomb per kilogram (C/kg)
What is the SI unit for Curie?
Becquerel (Bq)
Define Radioactivity
used to measure quantity of radioactive material (not the amount of radiation emitted but atoms decaying per second)
SI unit for radioactivity?
Becquerel (Bq)
Define stochastic effects
randomly occurring effects of radiation
- probability of occurrence is related to the dose of radiation
(increase dose = increase probability)
Define deterministic effects
Effects become more severe based on dose
- has a threshold dose
Define LET
Linear energy transfer:
The amount of energy deposited by radiation per unit length of tissue
Define RBE
Relative biological effectiveness:
ability to produce biological damage (varies w/LET)
What is direct effect?
radiation directly interacts with DNA in the cellular nucleus
What is indirect effect?
radiation interacts with water molecules in the cytoplasm of the cell
define radiolysis of water
radiation energy is deposited in the water of the cell resulting in an ion pair (positively charged water molecule and a free electron)
Law of Bergonie and Tribondeau
cells are most sensitive to radiation when they are immature, undifferentiated and rapidly dividing
What are the early somatic effects of radiation?
-Hematopoietic syndrome
- gastrointestinal syndrome (GI)
- Central nervous system
What are the late somatic effects of radiation?
-carcinogenesis
- cataractogenesis
- embryologic effects
- thyroid disfunction
- life span shortening
cardinal principles of radiation protection
time, distance, shielding
Define mean marrow dose
average dose of radiation to bone marrow
Unit of measurement for air kerma
gray (air) Gya
Calculate dose equivalent
(absorbed dose) x (radiation weighting factor)
Equation: (Sv) = (Gy) x (Wr)
What is Radiation weighting factor?
considers the biological impact of the type and energy of the the radiation used
What is the radiation weighting factor for x-rays/gamma rays?
Wr=1
What is tissue weighting factor?
considers the relative radiosensitivity of the organ or body part being irradiated
Unit of measurement for effective dose?
Sievert (Sv)
Unit of measurement of equivalent dose?
Sievert (Sv)
Calculate the effective dose
(absorbed dose) x (radiation weighting factor) x (tissue weighting factor)
Sv = (Gy) x (Wr) x (Wt)
What is the best protection against radiation exposure?
distance
Define Primary radiation
radiation exiting the x-ray tube
define exit radiation
xrays that emerge from the patient and strike the image receptor
(consists of primary and scattered photons)
Define heterogeneous beam
x-ray beam that has photons with different energies
Describe Photoelectric interaction
incident photon interacts with an inner orbital (K or L shell) electron. All energy is deposited into electron and is ejected from orbit able to ionize other atoms
photon is “absorbed”
Describe photoelectric effect
- The ejected electron from the inner shell leaves a vacancy
- electrons from the adjacent orbit drops down to fill the void
- as electron drops, excess energy is shed and released as a secondary photon
How are characteristic photons made?
through the photoelectric effect
Are Characteristic photons high or low energy
low energy
Describe Compton interaction
- incoming x-ray photon strikes an outer shell electron
- partial energy transfer to the electron
- electron is ejected from orbit
What is the compton electron?
The outer shell electron that is ejected during compton interaction
In the compton effect, what happens to the photon after the interaction with an outershell electron?
The photon continues on an alternate path with less energy causing the wavelength of the photon to be longer.
Coherent scatter is also known as?
classical scatter
Coherent scatter is produced by what type of photons?
low energy x-ray photons
Describe coherent scatter
- low energy x-ray photons do not remove but vibrate electrons
- through the vibration energy equal to original photon is emitted
- no ionization occurs
- may cause fog on images if kVp is higher than 70
What kVp does coherent scatter have no effect on?
<70 kvp
Describe Pair production
- involves an interaction between the incoming photon and the atomic nucleus
- must be high energy photon
- does not occur in radiography
What are the two primary photon - tissue interactions in diagnostic x-ray?
photoelectric and compton
What dose response relationship indicates the following:
- no level of radiation is completely safe
- a response occurs at every dose
- degree of response to exposure is directly proportional to amount of radiation recieved
Linear - non threshold relationship
Describe Linear - threshold relationship
- lower doses (below threshold) are expected to provide no response
- if threshold exceeded, response is directly proportional to dose received
What dose response relationship indicates the following:
- lower doses (below threshold) are expected to provide no response
- if threshold is exceeded the response is not directly proportional to the dose received and is increasingly effective per unit dose
nonlinear - nonthreshold relationship
Descrive nonlinear-nonthreshold relationship
- no level of radiation can be considered completely safe
- response occurs at every dose
- degree of response is not directly proportional to the dose recieved
- the effect is large even with a small increase of dose
What is the annual effective dose limit for occupational workers?
50 mSv
What is the annual equivalent dose limit for occupational workers lens of eye
150 mSv
What is the annual equivalent dose limit for occupational workers skin, hands and feet
500 mSv
Equation for Cumulative effective dose limit?
Age (in yrs) X 10 mSv
What is the annual effective dose for general public?
5 mSv
What is the maximum total equivalent dose for the gestation period?
5 mSv
What is the equivalent dose limit per month of an embryo-fetus?
0.5 mSv
What does RBE stand for?
Relative biologic effectiveness
Define RBE
The ability to produce biological damage (varies with LET)
Define somatic cells
not germ or reproductive cells
Somatic cells have what type of division process?
Mitosis
Define Germ cells
reproductive cells (sperm or ovum)
What type of division process is for germ cells?
meiosis
Exposure to somatic cells may result in what?
disruption in the ability of the organism to function
Exposure to germ cells may result in?
mutations that can be passed on to further generations
What is direct effect?
Radiation transfers its energy directly to the DNA or RNA
What are the results of direct effect?
- no effect (most common)
- alternation of cell structure and function
- cell death
- cell line death (failure of organ development)
- mutations, cancer, abnormal formations
What is indirect effect?
- Radiation energy interacting with water molecule
- resulting in a positively charged whater molecule (HOH+) and a free electron
- free radicals cause biological damage
What are the results of indirect effect?
- no effect (most common)
- formation of free radicals
- formation of (H2O2) hydrogen peroxide
What are free radicals?
highly reactive ions that have an unpaired electron in the outer shell
Most radiation induced damage to the body is a result of indirect or direct effect?
indirect - body is mostly water
What does OER stand for?
Oxygen enhancement ratio
Define OER?
cells that are more oxygenated are more susceptible to radiation damage
At what whole body dose dose the blood cell count begin to diminish?
25 rads
What is the most radiosensitive blood cell in the body?
lymphocytes
What is the radiosensitivity of epithelial tissue?
highly radiosensitive, divides rapidly
What is the radiosensitivity of muscle?
relatively insensitive, specialized cell (lacks division)
What is the radiosensitivity for adult nerve tissue
requires very high doses for damage response
What is the radiosensitivity of reproductive cells?
immature sperm cells = highly radiosensitive
ova and fetus = highly radiosensitive
Early deterministic effects
- erythema (skin reddening)
- epilation (hair loss)
- decreased blood count
What can occur from acute radiation syndrome?
- hematopoietic syndrome
- GI syndrome
- central nervous system (cerebrovascular syndrome)
Define Hematopoietic syndrome
decrease in total number of all blood cells
Define GI syndrome
death from serious damage to the lining of the intestines
Define Cerebrovascular syndrome
complete failure of nervous system and results in death from increased fluid in the brain
Late deterministic effects
-cataractogenesis (cataracts to form)
- thyroid problems (cancer or disfunction)
- fertility problems
Probabilistic effects is the same as?
Stochastic effects
Stochastic effects include?
- carcinogenesis
- nonmalignant radiodermatitis
- embryologic effects (most sensitive during 1st trimester)
- genetic mutation
Methods for beam limitation
- collimator
- cylinder cones
- aperture diaphragm
True or false: low energy xrays contribute to the diagnostic image?
False: low energy xrays only contribute to patient dose
What is beam hardening?
the removal of low energy rays resulting in a predominantly short wavelength, high energy beam.
More filtration does what to patient dose?
added filtration = lower patient dose
What are the two types of filtration?
added and inherent
What are examples of inherent filtration?
- glass envelope of the x-ray tube
- insulating oil around the tube
- diagonal mirror used for positioning light
What are examples of added filtration?
- aluminum sheets placed in the path of the beam near the xray tube window
- mirror placed in the collimator head
What is total filtration?
the overall total of inherent plus added filtration
what must be the total filtration aluminum equivalent for xray tubes?
2.5 mm aluminum equivalent
Define half-value layer
The amount of filtration that reduces the intensity of the xray beam to half its original value
The use of a grid increases what?
increase in patient dose due to a required increase of mAs
What is DAP
Dose area product :
the total of air kerma striking the surface of the patient
What is LIH
used in fluoroscopic procedures to display the most recently acquired image on the monitor
What is ABC or AERC?
Automatic brightness control
Automatic exposure rate control
(both are specific to fluoro)
What is the inverse square law?
as distance increases radiation dose decreases
What is the lead equivalent for a lead apron?
at least 0.25 mm lead equivalent
what is the lead equivalent for a thyroid shield
0.5 mm lead equivalent
How to reduce compton interactions?
increase collimation
What is the lead equivalent of a primary protective barrier?
1/16 inch lead equivalent
What is OSL?
Optically stimulated luminescence dosimeters
- use aluminum oxide
- unaffected by heat and humidity
- most radiosensitive
What is TLD’s
Thermoluminescent Dosimeters
- use lithium fluoride crystals
- medium radiosensitivity
What is a digital ionication dosimeter?
- has small ionization chamber
- stores electrical charge from radiation
- unaffected by environment
