Quantities and Units Flashcards
Why are there needs to develop standards for measuring and limiting radiation exposure?
- Awareness of potential harmful effects of ionizing radiation
- Desire of the medical community to reduce radiation exposure
How did Roentgen make his discovery?
through use of a Crookes tube, he coated a piece of paper with barium and it was illuminated
What are somatic injuries?
Injuries to the body including radiodermatitis and skin cancer
What were some results of excessive occupational radiation exposure for early pioneers?
- Radiodermatitis
- Cancer
- Blood disorders (aplastic anemia and leukemia)
What is radiodermatitis?
Lesions on fingers induced by ionizing radiation
What is skin erythema dose?
The dose which causes reddening of the skin as the upper limit
Why was skin erythema dose determined to be inefficient?
It was not reliable because of the varying levels in which people developed erythema
What were qualities needed in a new unit?
It needed to be based on some measurable effect produced by radiation, like ionization of atoms or energy absorbed in the irradiated object
When was the roentgen accepted as a unit of exposure?
1928 at the second internation congress of radiology
What are the early tissue reactions of ionizing radiation?
- Nausea
- Fatigue
- Diffuse redness of the skin
- loss of hair
- Intestinal disorders
- Fever
- Blood disorders
- Shedding of the outer layer of skin
What are the late tissue reactions of ionizing radiation?
- Cataract formation
- Fibrosis
- Organ atrophy
- loss of parenchymal cells
- Reduced infertility
- Sterility
What are Stochastic effects of ionizing radiation?
- Cancer
- Genetic (hereditary) effects
What is tolerance dose?
Radiation dose to which occupationally exposed persons could be subjected to without harmful effects
What happened in the Radiology Field in 1934?
Tolerance dose of 0.2 R per day because the standard recommended dose
What happened in the Radiology Field in 1936?
Tolerance dose was reduced to 0.1 R per day
Why was a replacement for tolerance dose needed?
Scientists began to recognize later deterministic somatic effects and late stochastic effects on people
When was the roentgen accepted as the internationally accepted unit of exposure?
1937
How were dose limits calculated in the 1970s?
They were calculated and established to ensure that risk from radiation exposure acquired on the job did not exceed risks encountered in safe occupations
What happened in the Radiology Field in 1980?
ICRU adapted SI units for use with Radiation
What are the traditional non-metric units of radiation?
- Exposure (X) - measured in R
- Absorbed dose (D) - measured in Rad
- Equivalent dose (EqD) - measured in REM
- Effective dose (EfD) - measured in REM
What is Exposure?
The total electrical charge (All + or all -) per unit mass that x-ray photons up to 3 million eV generated in dry, standard temp/pressure
How can Exposure (X) be defined further?
It is a radiation quantity, that expresses the concentration of radiation delivered to a specific area
What information must be obtained about an x-ray beam?
The amount of ionization the beam produces in a known mass of air
How is the measurement of beam ionization obtained?
In an accredited calibration laboratory using standard, or free-air ionization chamber
How does an ionization chamber work to measure radiation exposure by the amount of ionization an x-ray beam produces?
The chamber consists of a box with a known quantity of air, two oppositely charged metal plates and an electrometer, which measures the amount of charge collected on a positively charged plate
What is Coulomb (C)?
The basic unit of electrical charge
What do Coulombs represent?
The quantity of electrical charge flowing past a point in a circuit in 1 second when an electrical current of 1 ampere is used
What is ampere?
The SI unit of electrical current
What is C/kg used for?
X-ray equipment calibration and to calibrate radiation survey equipment
What is air kerma?
The SI quantity used to express how energy is transferred from a beam of radiation to a material such as patient skin
Why is air kerma important?
It denotes a calculation of radiation intensity in air
What can air kerma be used for?
To express x-ray tube output and inputs to the image receptor
What are the acronyms for kerma?
- Kinetic energy released in matter
- Kinetic energy release in material
- Kinetic energy released per unit Mass
What is air kerma expressed in?
Joule per kilogram (J/kg)
What else can air kerma be expressed in?
j/kg and may be stated in Gray
What is Gy(a)/?
Used to indicated kinetic radiation energy deposited or absorbed in a mass of air
What is Gy (t)?
Used to indicated kinetic radiation energy deposited or absorbed in a mass of tissue
What is Dose Area Product? (DAP)
The sum total of air kerma over the exposed areas of the patient’s surface
What is DAP usually specified in?
Units of mGY-cm^2
What is absorbed dose?
The amount of energy per unit mass absorbed by an irradiated object
What is absorbed dose responsible for?
Any biologic damage resulting from exposure of the tissues to radiation
What does absorbed dose depend on?
- atomic number of the tissue comprising the structure
- Mass density of the tissue
- energy of the incident photon
What is the SI unit of absorbed dose?
Gy
What can units of absorbed dose be used to measure?
The energy deposited by any form of radiation
What are the subunits used to indicated absorbed dose values?
-centigray (cGy) - 1/100
- milligray (mGy) - 1/1000
- micorgray (uGy) 1/1,000,000
What is the subunit conversion of Rad to centigray?
Number of rad / 1 = Number of cGy
What is surface integral dose? (SID)
The total amount of radiant energy transferred by ionizing radiation to the body during exposure
What is the equivalent SI unit for SID?
Gy-m^2
What is quality factor?
(Q) is an adjustment multiplier that is employed in the calculation of dose equivalence to detail the specific ability of a dose of any kind of ionizing radiation to cause biologic damage.
Which types of ionizing radiation have a quality factor of 1?
X-ray photons
Beta particles
Gamma photons
High-energy external photons
Which types of ionizing radiation have a quality factor of 5?
Thermal neutrons
Which types of ionizing radiation have a quality factor of 20?
Fast neutrons
Low-energy internal photons
Alpha particles
Mult. Charged particles of unknown energy
What is equivalent dose? (EqD)
The product of the average absorbed dose (D) in a tissue and its associated Wr (weighing factor) chose for that type
What is the formula for EqD?
EqD = D x Wr and Sv = Gy X Wr
What is Eqd expressed in?
SV or mSv
What is Radiation Weighing Factor (Wr)?
A dimensionless factor used for radiation protection purposes to account for differences in biologic impact amongst various types of ionizing radiation
Which types of radiation type/energy ranges have a Wr of 1?
x-ray and gamma ray photons and electrons (Every energy)
Which types of radiation type/energy ranges have a Wr of 2?
Protons
Which types of radiation type/energy ranges have a Wr of 5?
- Neutrons, energy <10 keV
- > 20 MeV
Which types of radiation type/energy ranges have a Wr of 10?
- 10 keV-100keV
- > 2 MeV-20MeV
Which types of radiation type/energy ranges have a Wr of 20?
- > 100 keV - 2 MeV
- Alpha particles
What is effective dose? (EfD)
A measure of the overall risk of exposure to humans from ionizing radiation
What is the formula for EfD?
EfD = D x Wr x Wt
What are tissue weighing factors? (Wt)
A value that denotes the percentage of the summed stochastic risk stemming from irradiation of tissue to the all-inclusive risk
What is linear energy transfer? (LET)
The amount of energy transferred on averaged by incident radiation to an object per unit length of track through the object
What is LET expressed in?
kiloelectron volts per micrometer
What is the general rule of LET?
Radiation with higher LET transfer a large amount of energy into a small area and can do more biologic damage
What are the typical values for absorbed dose to skin for AP lumbar spine exam?
6.4 mGy
What are the typical values for absorbed dose to bone marrow for AP lumbar spine exam?
0.6 mGy
What are the typical values for absorbed dose to a fetus for AP lumbar spine exam?
3.5 mGy
What are the typical values for equivalent dose to a fetus for AP lumbar spine exam?
3.5 mSv
What are the typical values for effective dose for AP lumbar spine exam?
3.3 mSv
What is Collective EfD used to describe in radiation protection?
internal and external dose measurements
What is the quantity of Collective EfD used to describe?
Radiation exposure of a population or a group from low doses of different sources of ionizing radiation
What is the radiation unit for Collective EfD?
Person-sievert
How is collective eFd calculated?
Total persons X Avg effective dose
What is total effective dose equivalent?
The sum of effective dose equivalent from external radiation and quantity called committed effective dose equivalent from internal radiation sources
What is TEDE?
Takes into account all possible sources of radiation exposure and is a useful dose monitor for occupational exposed personnel
