140 terms

Radiation Protection Ch. 4

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To be able to measure patient and personnel exposure in a consistent and uniform manner, diagnostic imaging personnel should:
be familiar with radiation quantities and units
German physics professor, Wilhelm Conrad Roentgen discovered x-rays on:
November 8, 1895
Roentgen passed electricity through a Crookes tube that he had covered with:
a shield made of black cardboard.
As Roentgen passed a charge through the pear-shaped, partial vacuum discharge tube, he observed light emanating from:
a piece of paper coated with barium platinocyanide.
The world's first x-ray picture on film clearly showed:
the bones of Roentgen's wife's hand
Somatic damage:
biologic damage to the body of the exposed individual caused by exposure to ionizing radiation
The word somatic comes from Greek term:
soma, meaning "of the body"
The first American radiation fatality:
Clarence Madison Dally (1865-1904)
Clarence Dally was:
glass-blower, tube maker, assistant, and longtime friend of fluoroscope inventor Thomas A. Edison.
Dally died of:
radiation-induced cancer in October 1904 at 39 years
Because of Clarence Dally's severe injuries and death, Thomas Edison:
discontinued his x-ray research.
Occupational exposure
radiation exposure received by radiation workers in the course of exercising their professional responsibilities
As a result of occupational exposure, many radiologists and dentists developed:
a reddening of the skin called radio dermatitis.
Blood disorders such as aplastic anemia, which results from bone marrow failure, and leukemia, an abnormal overproduction of white blood cells, were more common among:
early radiologists than among non radiologists.
From 1900 to 1930, the unit in use for measuring radiation exposure was called the:
skin erythema dose.
Skin erythema dose
the received quantity of radiation that causes diffuse redness over an area of skin after irradiation.
The First International Congress of Radiology was held in:
London, England, in 1925.
The International Commission on Radiation Units and Measurements (ICRU) was also formed in:
1925.
In 1928, a Second International Congress of Radiology was held in Stockholm, Sweden.
...
SI units were developed in:
1948
NCRP adopted SI units in 1985, but US still uses:
SI and traditional today.
Early deterministic somatic effects:
appeared within minutes, hours, days, or weeks of the time of radiation exposure.
Early deterministic somatic effects are believed to be preventable, if:
doses to radiation workers were limited and kept lower than a value at which no adverse biologic effects were demonstrated.
Tolerance dose
a radiation dose to which occupationally exposed persons could be continuously subjected without any apparent harmful acute effects, such as erythema of the skin.
Tolerance dose established today referred to as:
effective dose
Threshold dose
a radiation of radiation lower than which an individual has a negligible chance of sustaining specific biologic damage.
Late deterministic somatic effects and late stochastic effects:
Effects of ionizing radiation that appeared months or years following exposure to ionizing radiation
Genetic or Heritable Effects
Biologic effects of ionizing radiation on generations yet unborn
Early Deterministic Somatic Effects:
-Nausea
-Fatigue
-Diffuse redness of the skin (Erythema)
-Loss of hair (epilation)
-Intestinal disorders (diarrhea)
-Fever
-Blood disorders
-Shedding of the outer layer of the skin (desquamation)
Late Deterministic Somatic Effects:
-Cataract formation
-Fibrosis
-Organ atrophy (enlarged)
-Loss of parenchymal cells
-Reduced fertility
-Sterility
Late Stochastic Effects:
-Cancer
-Genetic (hereditary) effects
Stochastic means:
randomly occurring
Some occupations that are very hazardous are:
-deep sea diving
-professional mountaineering
Some nonhazardous occupations are:
-trade
-government desk work
The two most dangerous jobs:
logging and deep sea fishing
Hazardous jobs are determined by:
insurance companies
Even in nonhazardous occupations, there is still:
a small risk of fatality or serious injury (approximately 1 chance in 10,000 each year).
No amount of radiation is:
considered completely safe.
The probability of long-term harm, such as the development of cancer, was expected to:
decrease as the dose decreased, but it was not expected to become zero at any dose.
Effective dose (EfD) is based on:
the energy deposited in biologic tissue by ionizing radiation.
EfD takes into account the following:
1. The type of radiation (x-radiation, gamma, neutron)
2. The variable sensitivity of the tissues exposed to radiation.
The quantity, EfD, is actually a measure of:
the overall risk arising from the irradiation of biologic tissue and organs.
EfD takes into consideration the:
exposure to the entire body.
EfD is expressed in:
sieverts (Sv)
The SI unit of absorbed dose:
the Gray (Gy)
Radiation quantities:
- Exposure (X)
- Air kerma
- Absorbed dose (D)
- Equivalent dose (EqD)
- Effective dose (EfD)
Radiation Units:
- Coulombs per kilogram (C/kg)
- Gray (Gy)
- Gy
- Sievert (Sv)
- Sv
Unit of measure for radiation quantity Exposure:
R
Unit of measure for radiation quantity Absorbed Dose:
Rad
Unit of measure for radiation quantity Equivalent Dose:
Rem
Unit of measure for radiation quantity Effective Dose:
Rem
Radiation Unit for Exposure:
Coulombs per kilogram (C/kg)
Radiation unit for Air kerma:
Gray (Gy)
radiation unit for absorbed dose:
Gy
radiation unit for equivalent dose:
Sievert (Sv)
Radiation unit for effective dose:
Sv
When a volume of air is irradiated with x-rays or with gamma rays, the interaction that occurs between the radiation and neutral atoms in the air causes:
some electrons to be liberated from those air atoms as they are ionized.
As the intensity of x-ray exposure of the air volume increases,
the number of electron-ion pairs produced also increases.
The amount of radiation responsible for the ionization of a well-defined volume of air may be determined by measuring the number of electron-ion pairs or charged particles in that volume of air. This radiation ionization in the air is termed:
exposure.
Exposure (X)
the total electrical charge of one sign, either all pluses or all minuses, per unit mass that x-ray and gamma ray photons with energies up to 3 million electron volts (MeV) generate in dry air
Exposure is measured with:
a free-air ionization chamber
The radiation quantity that expresses the concentration of radiation delivered to a specific area, such as the surface of the human body is called:
Exposure
SI unit for Exposure:
Coulombs per kilogram (C/kg)
Traditional unit for Exposure:
roentgen (R)
Coulomb (C)
the basic unit of electrical charge.
Coulomb represents the:
quantity of electrical charge flowing past a point in a circuit in 1 second when an electrical current of 1 ampere is used.
The ampere is:
the SI unit of electrical current.
In the International System, the exposure unit is measured in :
Coulombs per kilogram (C/kg)
The roentgen is defined as:
the photon (either x-ray or gamma ray) exposure, that under standard conditions of pressure and temperature, produces a total positive or negative ion charge of 2.58 x 10 ^-4 C/kg of dry air.
Coulomb per kilogram (roentgen) unit is used for:
x-ray equipment calibration because x-ray output intensity is measured directly with an ionization chamber.
Precise Measurement of Exposure in Radiography
• Total amount of ionization (charge) an x-ray beam produced in a known mass of air must be obtained.
• Accomplished in lab by using a standard, or free-air, ionization chamber.
Units used away from the laboratory must be periodically recalibrated in a:
standardization laboratory against a free-air chamber.
Air kerma
SI quantity used to express radiation concentration transferred to a point, which may be at the surface of a patient's or radiographer's body
Air kerma actually denotes a:
Calculation of radiation intensity in air
X-ray tube output and inputs to image receptors are sometimes described in:
air kerma
Air kerma is:
kinetic energy released in a unit mass (kilogram) of air and is expressed in metric units of joule per kilogram (J/kg).
tissue kerma
kinetic energy released in a unit mass of tissue
Tissue Kerma is also given in units of:
joules per kilogram
Air kerma may be stated in Gray:
Gya for air kerma and Gyt for tissue kerma
Dose Area Product (DAP)
Total of air kerma over the exposed area of the patient's surface
Dose Area Product
a measure of the amount of radiant
energy that has been thrust into a
portion of the patients body surface
DAP is usually specified in units of:
mGy-cm2
Absorbed Dose (D)
The amount of energy per unit mass absorbed by the irradiated object.
Absorbed dose is responsible for:
biologic damage resulting from exposure of the tissues to radiation.
The amount of energy absorbed by a structure depends on:
-Atomic number (Z) of the tissues comprising the structure,
-Mass density of the tissue
-Energy of the incident photon
-Effective atomic number
Absorption increases as:
atomic number and mass density increase and also as photon energy decreases.
Low-energy photons are:
more easily absorbed in a material such as biologic tissue than are high-energy photons.
SI unit for absorbed dose:
gray (Gy)
Traditional unit for absorbed dose
rad (radiation absorbed dose)
Conversion factor for absorbed dose:
1 gray = 100 rad
The effective atomic number (Zeff) of a given biologic tissue is:
a "composite," or weighted average, of the atomic numbers of the many chemical elements comprising the tissue.
Bone has a higher effective atomic number than does soft tissue because:
bone contains calcium and phosphorus, whereas soft tissue is composed mostly of fat and structures close to that of water.
As energy increases, the difference in the amount of absorption between any two tissues of different atomic number:
decreases.
Because the process of absorption is responsible for biologic damage and absorption properties vary with the quality of the radiation and the type of tissue irradiated,
irradiation of tissues in therapeutic radiology is generally specified in terms of absorbed dose rather than in terms of exposure.
At all energies, mass density always has an effect on absorption. This effect is:
linear and proportional/
A material that is twice as dense as another will:
absorb twice as much energy from the same photon beam.
joule
the work done or energy expended when a force of 1 newton (N) acts on an object along a distance of 1 meter (m).
Surface integral dose (SID)
Total amount of radiant energy transferred by ionizing radiation to the body during a radiation exposure
Historically, the surface integral dose had been known as:
exposure area product
Equivalent SI unit for SID is the:
Gy-m2
Equal absorbed doses of different types of radiation produce different amounts of:
biologic damage in body tissue.
Quality Factor (Q)
adjusts the absorbed dose value
Linear Energy Transfer (LET)
Amount of energy transferred by
incident radiation to an object
per unit length of track through
the object.
High LET transfers large amount of energy into a small area and does more:
biologic damage than radiation with a low LET.
Equivalent Dose (EqD)
Product of the average absorbed dose in a tissue or organ in the human body and its associated radiation weighting factor (WR) chosen for the type and energy of the radiation in question.
Stochastic effects
nonthreshold, randomly occuring biologic effects of ionizing radiation such as cancer and genetic (hereditary) abnormalities.
SI unit for Equivalent dose:
sievert (Sv)
Traditional unit for equivalent dose:
rem
Conversion factor for equivalent dose:
1 sievert = 100 rem
Effective dose provides a measure of:
the overall risk of exposure to humans from ionizing radiation.
NCRP defines EfD as:
the sum of the weighted equivalent doses for all irradiated tissues or organs.
EfD incorporates both:
the effect of the type of radiation used (x-radiation, gamma, neutron) and the variability in radiosensitivity of the specific organ or body part irradiated through the use of appropriate weighting factors.
These factors determine the:
overall harm to those biologic components and the risk of developing a radiation-induced cancer or, for the reproductive organs, the risk of genetic damage.
The weighting factor that takes into account the relative detriment to each specific organ and tissue is called the:
tissue weighting factor.
Tissue weighting factor is used in the calculation of:
EfD.
The tissue factor is a conceptional measure for the relative risk associated with irradiation of different body tissues.
...
Tissue weighting factor
A value that denotes the percentage of the summed stochastic (cancer plus genetic) risk stemming from irradiation of tissue (T) to the all inclusive risk, when the entire body is irradiated in a uniform fashion
Tissue weighting factor accounts for:
the risk to the entire organism brought on by irradiation of individual tissues and organs.
Incorporates type of radiation and
radiosensitivity of the part through
weighting factors:
Effective dose
SI unit for effective dose:
sievert
Traditional unit for effective dose:
rem
Absorbed Dose (D) is responsible for:
biologic damage.
Value denoting the percentage of the summed stochastic risk stemming from irradiation of tissue to the all-inclusive risk
Tissue weighting factor
Tissue weighting factor assigns:
risks for potential biologic responses from various types of radiation on a common scale
Because radiation doses for radiation workers employed in diagnostic radiology are relatively small, they may be specified in terms of:
mSv.
The quantity, collective effective dose (ColEfD), is used to:
describe radiation exposure of a population or group from low doses of different sources of ionizing radiation.
Collective effective dose (ColEfD) is determined as the:
product of the average dose for an individual belonging to the exposed population and the number of persons exposed.
The radiation unit for the quantity ColEfD
person-sievert
Total Effective Dose Equivalent (TEDE)
A radiation dosimetry quantity that was defined by NRC to monitor and control human exposure to ionizing radiation.
TEDE is designed to:
take into account all possible sources of radiation exposure.
TEDE
"the sum of effective dose equivalent from external radiation exposure and a quantity called committed effective dose equivalent (CEDE) from internal radiation exposures."
useful dose monitor for occupationally exposed personnel such as nuclear medicine technologists and interventional radiologists, who are likely to receive possibly significant radiation exposure during the course of a year
TEDE
What is the equivalent of the SI unit sievert?
Rem
What was used as the first measure of exposure for ionizing radiation?
skin erythema
What is the unit of collective effective dose (ColEfD)?
person-sievert
The concept of tissue weighting factor is used to do what?
Account for the risk of the entire organism brought on by irradiation of individual tissues and organs
To convert the number of grays into milligrams, the number of grays must be:
multiplied by 1000
What does the SI radiation unit coulomb per kilogram measure?
radiation exposure in air only
What radiation quantities accounts for some biologic tissues' being more sensitive to radiation damage than other tissues?
equivalent dose
What is the SI unit for surface integral dose?
Gy-m2