Units, Detection, and Measurement

217 Topic 2

Occupational Exposure

Radiation exposure received in the course of exercising professional responsibilities, referring to all exposures received in the workplace

Radiodermatitis

A reddening of the skin developed by many early radiologists and dentists using the new penetrating rays

Skin Erythema Dose

The received quantity of radiation that causes diffuse redness over an area of skin after irradiation, used between 1900 and 1930

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, which could be regarded as a threshold dose

Threshold Dose

A dose of radiation lower than which an individual has a negligible chance of sustaining specific biologic damage

Maximum Permissible Dose (MPD)

The radiation protection quantity that replaced the tolerance dose in the 1950s, initially expressed in rem

Effective Dose (EfD)

A measure of the overall risk arising from the simultaneous irradiation of various biologic tissues and organs within an individual, which is based on the energy deposited in biologic tissue by ionizing radiation and takes into account both the type of radiation and the variable sensitivity of the tissues exposed

Medical Exposure

Radiation exposures from diagnostic and therapeutic procedures, including individuals assisting patients with these procedures

Public Exposure

All radiation exposures other than occupational and medical exposures

Exposure

The amount of radiation responsible for the ionization of a well-defined volume of air, determined by measuring the number of electron-ion pairs

Coulomb (C)

The basic unit of electrical charge, equal to the amount of electrical charge moving past a point in a conductor in 1 second when an electrical current of 1 ampere is used

Coulombs per Kilogram (C/kg)

An exposure unit equal to an electrical charge of 1 Coulomb produced in a kilogram of dry air by ionizing radiation

KERMA

Kinetic Energy Released per unit Mass, with the unit J/kg

Air Kerma

An SI quantity used to express the total kinetic energy released in a unit mass of air, expressing radiation concentration transferred to a point

Dose Area Product (DAP)

The sum total of air kerma over the exposed area of the patient's surface, usually specified in mGy

cm²

Activity

The number of radionuclides disintegrating per second, with the SI unit becquerel (Bq) and conventional unit curie (Ci)

Absorbed Dose (D)

The amount of energy per unit mass absorbed by an irradiated object, with the SI unit gray (Gy) and conventional unit radiation absorbed dose (rad)

Quality Factor (Q)

An adjustment multiplier employed in the calculation of dose equivalence to detail the ability of a dose of any kind of ionizing radiation to cause biologic damage

Linear Energy Transfer (LET)

The amount of energy transferred on average by incident radiation to an object per unit length of track or passage through the object, expressed in keV/µm

Radiation Weighting Factors (WR)

A dimensionless factor chosen to account for differences in biologic impact among various types of ionizing radiation

Equivalent Dose (EqD)

The product of the average absorbed dose and the radiation weighting factor, which depends on the type of radiation

Tissue Weighting Factors (WT)

Factors that specifically take into account the relative detriment to each specific particular organ and tissue

Collective Effective Dose (ColEfD)

The sum of individual doses received in a given period of time by a specified population from exposure to a specified source of radiation, expressed in person-sieverts

Total Effective Dose Equivalent (TEDE)

A radiation dosimetry quantity defined by the Nuclear Regulatory Commission (NRC) to monitor and control human exposure to ionizing radiation, calculated as the sum of effective dose equivalent from external radiation exposures and Committed Effective Dose Equivalent (CEDE) from internal radiation exposures

CT Dose Index (CTDI)

A parameter determined by an ionization measurement using a long, pencil-like, cylindrical ionization chamber inserted into a cylindrical acrylic phantom, representing the dose to any point in the patient including scatter from CT slices in both directions

CTDIW

A weighted average of two measured CTDI values

CTDIVOL

The average absorbed dose within the scanned volume

Pitch

The relationship between the movement of the couch and the X-ray beam collimator dimension

Dose Length Product (DLP)

A CT parameter representing the product of CTDIVOL and the irradiated scan length, characterizing the volumetric extent along the patient's body that has been irradiated

Scan Length

A CT dose parameter derived from the product of slice width, the number of slices, and pitch

Roentgen (R)

The conventional unit associated with exposure, defined as the photon exposure that, under standard conditions of pressure and temperature, produces a total positive or negative charge of 2.58 × 10^-4 C/kg of dry air

Rem (radiation equivalent man)

The traditional unit used for radiation protection purposes, defined as the dose equivalent to any type of ionizing radiation that produces the same biologic effect as 1 rad of radiation absorbed dose of X-radiation

Electron Volt (eV)

The energy acquired by an electron when it is moved through a 1-V potential difference by a battery or some other mechanism

Hertz (Hz)

The standard unit for frequency, equal to one repeatable cycle of a phenomenon or event occurring in 1 second

Committed Effective Dose Equivalent (CEDE)

A measure of the probabilistic health effect on an individual resulting from an intake of radioactive material into the bod