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Chapter 4
Radiation Quantities and Units
| Term | Definition |
|---|---|
| absorbed dose | amount of energy per unit mass absorbed by an irradiated object; uses an SI unit of gray (Gy) |
| air kerma | SI quantity that can be used to express radiation energy transferred to a point; kinetic energy released in a unit mass (kg) of air and is expressed in metric units of J/kg |
| collective effective dose (ColEfD) | designated for use in the description of a population or group exposed to different individual amounts of ionizing radiation; equal to the sum of all of the doses times the # of individuals exposed and would be expressed in units such as person-Sievert |
| committed effective dose equivalent (CEDE) | measure of the probabilistic health effect on an individual as a result of intake of radioactive material into the body; takes into account the length of time that the radioactive material may stay within the body |
| coulomb (C) | basic SI unit of electrical charge; 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 |
| coulomb per kilogram (C/kg) | SI unit of radiation exposure; can be used for x-ray equipment calibration |
| dose area product (DAP) | the sum total of air kerma over the exposed area of the patient's surface |
| early tissue reactions | reactions in biologic tissues that are dependent on the duration of time after the exposure to ionizing radiation; they appear within minutes, hours, days, or weeks of the time of exposure; these reactions are precipitated by cell death |
| effective dose (EfD) | quantity that is used for radiation protection purposes to provide a measure of the overall risk of exposure to humans from ionizing radiation; takes into account the dose from all types of ionizing radiation to various irradiated organs or tissues |
| equivalent dose (EqD) | quantity that attempts to numerically specify the differences in transferred energy; is the product of the average absorbed dose in a tissue or organ in the human body and its associated radiation weighting factor; enables calculation of EfD |
| exposure (X) | amount of ionizing radiation that may strike an object, when in the vicinity of a radiation source; measured in SI units of C/kg or traditional units of R |
| genetic or hereditary effects | biologic effects of ionizing radiation on future generations due to irradiation of germ cells in previous generations |
| gray (Gy) | SI unit of absorbed dose and air kerma |
| International System of Units (SI) | common units that makes possible a standard system of units among all branches of science throughout the world |
| late tissue reactions | nongenetic consequences of radiation exposure that appear months or years afterward; these effects may be either stochastic or tissue reactions |
| linear energy transfer (LET) | the mean quantity of energy deposited by ionizing radiation in an object per unit length of track as it passes through the object; it is expressed in units of keV/µm |
| occupational exposure | radiation exposure received by radiation workers (occupationally exposed persons) in the course of exercising their professional responsibilities |
| radiation weighting factor | a dimensionless factor (a multiplier) that was chosen for radiation protection purposes to account for differences in biologic impact among various types of ionizing radiations; places risks associated with biologic effects on a common scale |
| Sievert (Sv) | SI unit of measure for equivalent dose (EqD) and effective dose (EfD); it is the product of the absorbed dose and the radiation weighting factor |
| somatic damage | damage caused by biologic reactions in tissues of the body that were irradiated that can be directly related to the dose of ionizing radiation received; can result in severe injuries and/or death |
| stochastic effects | mutational or randomly occurring biologic changes, independent of dose, in which the chance of occurrence of the effect rather than the severity of the effect is proportional to the dose of ionizing radiation; occur months or years after high level doses |
| tissue weighting factor | a value that denotes the percentage of the summed stochastic (cancer plus genetic) risk stemming from irradiation of specific tissues to the all-inclusive risk when the entire body is irradiated in a uniform fashion |
| total effective dose equivalent (TEDE) | a system of units and quantities used to monitor occupationally exposed personnel; sum of the EfD from external radiation exposures and the CEDE from internal sources; designed to take into account all possible causes of radiation exposure |
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