Chapter 4: Radiation Quantities and Units Flashcards
who discovered xrays
wilhelm conrad roentgen
when was xrays discovered
November 8, 1895
with what was xrays discovered
with crookes tube
First xray image
roentgens wifes hand
who was the first fatality
Clarence Dally thomas edison assistant
what was the crookes tube then updated to
Coolidge tube
devised a FLUOROSCOPE using a fluorescing screen
-dynamic
Thomas edison
when did clarence dally die
October in 1904
What place did Conrad discovered x-rays
the university of wurzburg Germany bavaria
what was the paper coated with for the tube to be energized
barium platinocyanide
- Awareness of potential harmful effects of ionizing radiation
Desire of the medical community to reduce radiation exposure throughout the world by developing standards for measuring and limiting this exposure
Reasons diagnostic imaging personnel should be familiar with
radiation quantities and units
greek term “soma” means
of the body
Among physicians, cancer deaths attributed to x-ray exposure were reported as early as
1910
Result of excessive occupational radiation exposure for early pioneers and excessive exposure of patients
Radiodermatitis
Cancer
Blood disorders
somatic
to yourself
genetic
future generations
many radiologists and dentists using the new penetrating rays developed a reddening of the skin called
radiodermatitis.
when were committees being started
1910
first death was 1904
best overall dose
effective dose
Unit used from 1900 to 1930 to measure radiation exposure Problems encountered in using the skin erythema dose as a way to measure radiation exposure
Need to find a more reliable unit
New unit selected to be based on some exactly measurable effect produced by radiation, such as ionization of atoms or energy absorbed in the irradiated object
- Because the amount of radiation required to produce an erythema reaction varied from one person to another
Skin Erythema Dose
early tissue reactions appear within
minutes, hours, days, or weeks of the time of radiation exposure, were believed to be preventable if doses to radiation workers were limited.
Early tissue reactions
- Nausea
- Fatigue
- Diffuse redness of the skin
- Loss of hair
- Intestinal disorders
- Fever
- Blood disorders
- Shedding of the outer layer of skin
Late tissue reactions
- Cataract formation
- Fibrosis
- Organ atrophy
- Loss of parenchymal cells
- Reduced fertility
- Sterility
Stochastic effects
- Cancer
- Genetic (hereditary) effects
stochastic
random
meaning nothing is safe
nonthreshold
is a radiation dose to which occupationally exposed persons could be subjected without any apparent harmful acute effects, such as erythema of the skin
tolerance dose (threshold dose)
meaning up to a certain point, your fine after that you start seeing reactions
Threshold
Concept of tolerance dose
Threshold dose
a dose of radiation lower than which an individual has a negligible chance of sustaining specific biologic damage
threshold dose
is recommended as a tolerance daily dose limit in 1934
0.2 R (roentgens)
is recommended as a tolerance daily dose limit in 1936
0.1 R
late reactions time period
couple months and years
becomes internationally accepted as the unit of measurement for exposure to x-radiation and gamma radiation in 1937.
Roetgen
radiation exposure received in the course of exercising professional responsibilities, many radiologists and dentists using the new penetrating rays developed a reddening of the skin called radiodermatitis.
occupational exposure
replaced the tolerance dose for radiation protection purpose in 1950s
maximum permissible dose (MPD)
The rem has since been replaced by the SI unit
sievert
Based on the energy deposited in biologic tissue by ionizing radiation, it takes into account both of the following: the effective dose
The type of radiation (e.g., x-radiation, gamma, neutron)
2. The variable sensitivity of the tissues exposed to the radiation
The International System of Units (SI) is developed. what year
1948
he ICRP replaces effective equivalent dose with the term effective dose (EfD). what year
1991
The SI unit of absorbed dose
gray (Gy)
who created the gray
Louis Harold Gray
ionization produced in air.
exposure
deposition of energy per unit mass in any material from exposure to ionizing radiation.
absorbed dose
is a quantity that builds upon D but then takes into account the type of radiation striking an object
equivalent dose
builds upon EqD by adding an attempt to take into account the different harmful degrees of radiation effects on the parts of the body that are being irradiated to arrive at an index of overall harm to a human
effective dose
The quantity equivalent dose uses radiation weighting factors (WR)
to adjust the value of the absorbed dose to reflect the different capacity for producing biologic harm by various types and energies of ionizing radiation
The quantity effective dose uses tissue weighting factors (WT)
to adjust the quantity equivalent dose to reflect the difference in harm to the person as a whole depending on the tissues and organs that have been irradiated. Therefore, effective dose takes into account both the type of radiation and the part of the body irradiated.
Units for exposure
Coulombs per kilogram
units for air kerma
gray
Units for absorbed dose
gray
Units for equivalent dose and effective dose
Sievert
is the total electric charge of one sign, either all plus or all minus, per unit mass that x-ray and gamma ray photons with energies up to 3 million electron volts (MeV) generated in dry (i.e., nonhumid) air at standard temperature (22° C) and pressure (760 mm Hg or 1 atmosphere at sea level).
exposure
It is a radiation quantity “that expresses the concentration of radiation delivered to a specific area, such as the surface of the human body.
exposure
This type of direct measurement is normally accomplished in an accredited dosimetry calibration laboratory (ADCL) by using a standard, or free-air,
ionization chamber
chambers collected electrical charge of 2.58 x 10-4 c/kg of irradiated air constitutes an exposure
of 1 roentgen R
The basic unit of electric charge
It is equal to the “amount” of electrical charge moving past a point in a conductor in 1 second when an electric current amounting to 1 ampere is used
coulomb (c)
The SI unit of electric current
Ampere
SI unit of measure for the radiation quantity, exposure, is equal to an electric charge of 1 C produced in a kilogram of dry air by ionizing radiation.
Coulomb per kg
Acronym for
Kinetic energy released in air
Kinetic energy released in material
Kinetic energy released per unit mass
Air Kerma
Gradually replacing the traditional quantity, exposure
Denotes a calculation of radiation intensity in air
Quantity that can be used to express x-ray tube output and inputs to image receptors
Air Kerma
SI quantity used to express how energy is transferred from a beam of radiation to a material such as the patient’s skin
Air Kerma
Expressed in metric units of joule per kilogram (J/kg)
May be stated in Gy
When the Gy is used to indicate kinetic radiation energy deposited or absorbed in a mass of air, it is written as Gya.
When the Gy is used to indicate kinetic radiation energy deposited or absorbed in a mass of tissue, it is written as Gyt.
air kerma
Is the sum total of air kerma over the exposed area of the patient’s surface, or a measure of the amount of radiant energy that has been thrust into a portion of the patients body surfaceIs usually specified in units of mGy-cm2
Dose area product (DAP)
This quantity is the amount of energy per unit mass absorbed by an irradiated object
Absorbed Dose
It is responsible for any biologic damage resulting from exposure of the tissues to radiation.
Some structures in the body can absorb more radiant energy than others
Absorbed Dose
The amount of energy absorbed by a structure depends on the
Atomic number (Z) of the tissue comprising the structure
Mass density of the tissue
Energy of the incident photon
The Si unit of absorbed dose is :
milligray
Units for the following :
- in the air
- hit tissue
- scatter
-field of view
- how much tissue are you radiating
Dose area product
is the amount of energy transferred on average by incident radiation to an object per unit length of track, or passage, through the object and is expressed in units of kiloelectron volts per micrometer (keV/µm)
linear energy transfer (LET)
Quality Factor of xray
1
quality factor of beta
1
quality factor of gamma
1
quality factor of alpha
20
quality factor of x-ray, beta, and gamma
1
quality factor for fast neurons
20
Is the product of the average absorbed dose in a tissue or organ in the human body and its associated WR chosen for the type and energy of the radiation in question
EqD
Used for radiation protection purposes when a person received exposure from various types of ionizing radiation
For measuring biologic effects may be determined and expressed in Sv or in a subunit of the Sv
EqD
tissue is only used with which dose
effective
D x WR and Sv = Gy x WR
EqD
Must be used when determining EqD
Is a dimensionless factor (a multiplier) used for radiation protection purposes to account for differences in biologic impact among various types of ionizing radiation
Places risks associated with biologic effects on a common scale
Radiation Weighting Factor (WR)
Provides a measure of the overall risk of exposure to humans from ionizing radiation
EfD
how much was absorbed in the body + type of radiation
equivalent dose
Takes into account the relative detriment to each specific organ and tissue
Used in the calculation of EfD
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
Accounts for the risk to the entire organism brought on by irradiation of individual tissues and organs
Tissue Weighting Factor (WT)
“The sum of the weighted equivalent doses for all irradiated tissues or organs” (NCRP Report No. 116)
Incorporates both the effect of the type of radiation used and the variability in radiosensitivity of the organ or body part irradiated through the use of appropriate weighting factors
These factors quantify the overall potential harm to those biologic components and the risk of developing a radiation-induced cancer or, for the reproductive organs, the risk of genetic damage.
EfD
D × WR × WT
EfD
Quantity used to describe radiation exposure of a population or group from low doses of different sources of ionizing radiation
Collective EfD
Person-sievert is the radiation unit for this quantity
Collective EfD
Used in radiation protection to describe internal and external dose measurements
Collective EfD
is another SI quantity that is used to express how energy is transferred from a beam of radiation to air. It is mostly replacing the traditional quantity, exposure.
Air Kerma
A radiation dosimetry quantity that was defined by the NRC to monitor and control human exposure to ionizing radiation
Total Effective Dose Equivalent (TEDE)
is defined as the amount of energy per unit mass absorbed by an irradiated object
Absorbed Dose
Described by NRC regulations as “the sum of effective dose equivalent from external radiation exposure and a quantity called committed effective dose equivalent (CEDE) from internal radiation exposures.
Traditionally, the whole-body TEDE regulatory limit is
0.05 Sv for occupationally exposed personne
how much Tede for the general public
0.001 Sv for the general public
Determined as the product of the average EfD for an individual belonging to the exposed population or group and the number of persons exposed
Collective EfD
If 200 people receive an average effective dose of 0.25 Sv, the collective effective dose is
(200)(0.25)= 50 person - sieverts
