Ablation

means removal or destruction.

Absorbed dose

is a measure of the energy imparted by ionizing radiation per unit mass of irradiated material. The units of absorbed dose are the gray and the rad.

Absorption of radiation

is the process through which radiation deposits some or all of its energy as it passes through matter.

Activity—

see Radioactivity.

Acute radiation injury

is an injury that manifests itself within the first several weeks after exposure to radiation.

Angiography

is the study of blood vessels, usually using x-rays and a pharmaceutical called a contrast agent.

Anode

is a positively charged electrode. Negative ions are attracted to anodes.

Atoms

are the smallest particles with which an element can enter into a chemical reaction. Atoms are characterized by an atomic number describing their proton number and elemental identity and by an atomic mass number that varies according to the total number of protons and neutrons in the atom.

Attenuation of radiation

is the reduction in intensity that occurs as radiation interacts with matter. Attenuation occurs through a combination of scattering and absorption.

Authorized user

means an individual who is identified as an authorized user on a license for the medical use of radioactive material.

Background radiation

is naturally occurring radioactivity and radiation caused by cosmic rays.

Beta particles

are electrons (beta-minus) or positrons (beta-plus) that are emitted by the nucleus of a radioactive atom.

Biological half-life

is the time required for the body or an organ system to eliminate half of the dose of an administered compound.

Brachytherapy

is radiation therapy using sealed radioactive sources placed inside or on the surface of the patient. These may be intercavitary (within body cavities), interstitial (within tissues), after loaded (i.e., put in after tubes, holders, etc., to contain them are placed in the patient), high dose rate (i.e., using large amounts of radioactivity to get the maximum effect in a short time), or low dose rate.

Byproduct material

is defined under the Atomic Energy Act of 1954, 42 SC 2014 Sec. 11(e) to mean: (1) any radioactive material (except special nuclear material) produced during the process of producing or utilizing special nuclear material, and (2) the tailings or wastes produced during the extraction or concentration of uranium or thorium from any ore. This latter category is of no relevance in medicine.

Cancer

is the commonly used term for any malignant neoplasm.

Chain reaction

denotes any process in which some of the reaction products become reaction raw materials. In particular, nuclear reactors consume and produce neutrons simultaneously as nuclei fission in a chain reaction.

Chemotherapy

is the treatment of disease with chemical compounds. The term is generally used in connection with the use of chemical for treatment for malignant disease.

Committed effective dose equivalent

is the sum of the products of the applicable weighting factors for each of the body organs or tissues that are irradiated multiplied by the committed dose equivalent to that area.

Computed tomography (CT),

or x-ray transmission computed tomography, is an x-ray technique in which the x-ray tube and possibly the detector are rotated around the patient; the detected signal produced by transmitted x-rays is processed by a computer to create transaxial images of x-ray attenuation in the patient. The technique enhances contrast by decreasing the contribution of scattered x-rays to the image.

Contamination, radioactive,

is the deposition of radioactive material where its presence is not desired.

Contrast agents

are pharmaceuticals used to enhance the distinction of bright and dark tones of images by changing some property in the patient. Many x-ray contrast agents contain iodine or barium, which attenuate x-rays more than the elements in the body.

Contrast of images

refers to the distinction between bright and darktones.

Cosmic rays

are radiation that originates outside the earth's atmosphere.

Curie (Ci)

is the unit of radioactivity used in the older literature; it is equal to 3.7 × 10¹⁰ disintegrations per second. The Système Internationale d'Unités

(SI) unit supplanting the curie is the becquerel (Bq), where 1 Bq = 1 disintegration per second.

Cyclotron

is a device used for accelerating charged particles in a spiral path to create high-energy particles.

Decay, radioactive,

is the disintegration of the nucleus of an atom with the emission of radiation, representing a release of mass, energy, or both. This process may also be referred to as nuclear or radioactive disintegration.

Decay in storage (DIS)

means allowing radioactive materials with short half-lives to decay to background levels in storage facilities, then disposing of them by conventional waste disposal methods.

Deterministic (nonstochastic)

means that the intensity of a radiobiologic effect is related to the amount of exposure. In such an effect there is believed to be a threshold below which the effect is not seen.

Dosage

is the amount of a material administered. Dosages may be incorrectly referred to as doses.

Dose

is the energy delivered to the body by radiation. It is a generic term encompassing absorbed dose, dose equivalent, effective dose equivalent, committed dose equivalent, committed effective dose equivalent, or total effective dose equivalent. (See 10 CFR 20.1003.)

Dose equivalent

is a concept for modifying the absorbed dose to take into account the body part exposed, the dose rate, the age of the exposed person, and the type of radiation involved, such as photons, alpha, or other heavy or multiply charged particles, neutrons of unknown energy, or high-energy protons. The dose equivalent is the product of the absorbed dose in tissue, the quality factor for the radiation, and all other necessary modifying factors for the anatomic location. The unit for dose equivalent is the sievert.

Dose rate

is the rate at which radiation energy is delivered.

Dosimetrist

is an individual who calculates radiation doses, usually for radiation therapy.

Dosimetry

is the measurement of radiation doses.

Effective dose equivalent (EDE)

is the sum of the products of the dose equivalent to the organ or tissue and the weighting factors applicable to each of the organs or tissues that are irradiated. Its purpose is to put radiation doses to different anatomic locations on an equivalent basis for creating estimates of doses to populations.

Electrons

are negatively charged particles that surround the nucleus of an atom and determine its chemical properties. The mass of an electron is 1/1,835th the mass of a proton.

Element

is a pure substance consisting of atoms of the same atomic number. The atoms will contain the same number of protons, but a naturally occurring

element may be a mixture of isotopes—nuclei with different numbers of neutrons.

Epilation

is the loss of hair, either temporary or permanent.

Error

is a term used in several ways. In the narrow sense, it means a mistake or incorrect conclusion. In the broader sense, ''error" is used as a synonym for "uncertainty" in statistics; thus one talks about the "standard error of the mean," which reflects a statistical uncertainty.

Erythema

is a reddening of the skin resulting from radiation exposure. At one time it was used as a measure of the radiation dose received.

External dose

means that portion of the dose equivalent received from radiation sources outside of the body.

Extrapolation

means making an estimate of an effect from data acquired beyond the range of interest. Its opposite is interpolation, in which estimates are made of values between acquired data points.

Fission

means "splitting"; nuclear fission is the splitting of atoms into two or more parts of significant mass. Large amounts of energy, representing the difference in binding energy of the particles in the original nucleus and in the final particles, are released. Nuclear fission is the energy-producing mechanism exploited in the nuclear power reactor.

Fluoroscopy

is x-ray imaging of changes in the body or the distribution of a contrast agent in real time.

Gamma rays

are short-wavelength electromagnetic radiation (photons) that is emitted from the nucleus.

Gray (Gy)

is an SI unit of absorbed radiation dose, equal to an imparted energy of 1 joule per kilogram of matter. The older unit was the rad; 100 rads = 1 Gy.

Half-life

is the time it takes for half of the substance under consideration to disappear. If the value is unqualified, for radioactive materials, half-life refers to the physical half-life, which is a property of the decay of the radionuclide under consideration.

Interstitial

means "between cells."

Ion

means a charged atom, either positive or negative.

Ionizing radiation,

in the broadest sense, is any radiation that removes electrons from atoms (or molecules). This radiation comes from natural sources, such as cosmic radiation or naturally occurring elements such as radium, uranium, thorium, and radon. It also comes from anthropogenic (human-made) materials, such as those produced in a nuclear reactor. Finally, the radiation comes from machines such as x-rays and fluoroscopes. Ionizing radiation in medicine for both diagnostic and therapeutic purposes is derived from a

number of sources: (1) reactor-generated byproduct material and special nuclear materials produced in reactors, naturally occurring and accelerator-produced radioactive materials, and (3) x-ray machines and particle accelerators.

Isotopes

are a group of atoms that have the same proton number but different numbers of neutrons. Because the proton number determines the elemental identity, a discussion of isotopes is properly a discussion of different nuclides of the same element. The word "isotope" has been improperly used over the years to mean radioactive material or radionuclides.

Linear accelerator

is a device for accelerating a charged particle. It is commonly used in radiation therapy.

Late radiation injury

refers to radiation-induced cancer diagnosed a few to many years after exposure.

Linear

means a straight line or a direct relation between a dependent and an independent variable.

Linear, no-threshold model,

means the extrapolation of late and genetic radiation effects to low dose levels in a linear or straight-line fashion from data obtained at higher doses. It is presumed to define the upper limit of estimated effects.

Magnetic resonance imaging (MRI)

is the production of images from small signals emitted by hydrogen nuclei when, in a magnetic field, they return from an excited state to the ground state. Ionizing radiation is not used in MRI.

Malignant

connotes a tumor that is capable of metastasis or spreading to remote anatomic sites.

Manhattan Project

was the code name for the World War II effort to create a sustained fission reaction and an explosive device from that reaction. The resources and effort concentrated in this project rapidly developed much of what we know about radioactive materials today.

Maximum permissible dose (MPD)

is the maximum absorbed dose per unit time allowed to a particular type of individual, such as a member of the public or a radiation worker. There is no MPD for patients.

Medical institution

means an organization in which several medical disciplines are practiced (this is the Nuclear Regulatory Commission's (NRC) definition). In the broader usage, medical institution and hospital are synonyms. A hospital is a place where high-intensity procedures, such as surgery with anesthesia, are performed. This is in contrast to a physician's office, where only low-intensity procedures might be performed, or to a free-standing imaging center, where only imaging might be performed.

Metabolism

is the sum of all the physical and biological processes that produce and maintain a living organism.

Metastasis

means the spread of malignant cells beyond their original anatomic site.

Microcurie

means 1/1 millionth of a curie, or 3.7 × 10⁴ disintegrations per second.

Milliroentgen

means 1/1,000th of a roentgen, or 0.001 R.

Misadministration

means, in common parlance, the usage of the wrong pharmaceutical or treatment or the wrong amount, on the wrong patient, or at the wrong time. For the meaning that the NRC uses, see 10 CFR 35.2; it is noted that the definition has changed over time, so it and any statistics on misadministrations involving byproduct materials should be related to the definition in force at the time of reporting.

NARM

stands for naturally occurring and accelerator-produced radioactive material and stands in direct opposition to reactor-generated byproduct material. NARM and x-rays are not regulated under the Atomic Energy Act.

Naturally occurring radioactive material

are those materials that occur naturally in the universe and that spontaneously decay to emit radiation. The first of these to be exploited medically for its radioactive properties was radium.

Neutron

is a neutral nuclear particle of mass almost equal to that of the proton.

Nondeterministic (stochastic)

is applied to effects in which the likelihood of an event, but not the seriousness or intensity, varies with the amount of exposure.

Nuclear medicine

is a branch of medicine that uses very small (tracer) amounts of pharmaceuticals labeled with radioactive materials for diagnosis and therapy. Much of the diagnosis is accomplished by imaging the distribution of the radiopharmaceutical within the body; body functions and metabolism may therefore be studied without disruption. Radiation therapy with these unsealed sources may be targeted to particular tissues.

Nuclear reactor

is a device in which a nuclear fission reaction may be self-sustaining. In medicine, nuclear reactors may be used to create radioactive materials for administration to patients for both diagnostic and therapeutic purposes and to produce teletherapy sources. A reactor may also be used as a source for thermal or epithermal neutrons to irradiate a boron compound in a patient's tumor so that it becomes a source of ionizing radiation in the patient. This is referred to as boron-neutron capture therapy.

Nuclide

denotes any nucleus and its orbital electrons. It is a synonym for atom or element, but often is used when a particular mass number is being discussed.

Occupational exposure

(using the NRC's definition of occupational dose) means radiation exposure to an individual in a restricted area or in the course of employment in which the individual's assigned duties involve exposure to radiation. It does not include background radiation, medical radiation

exposure, exposure during voluntary participation in medical experiments, or as a member of the general public. (See 10 CFR 20.1003.)

Oncology

is the study of the genesis and proliferation of malignant tissue and refers to the medical discipline responsible for the diagnosis and treatment of patients with malignancies.

Palliative radiation therapy

means the use of radiation to contribute to a patient's comfort and decrease pain, but not necessarily to prolong life or "cure" a disease.

Particle accelerators

produce accelerated charged particles that range from electrons to heavy protons and ions such as carbon and argon. These particles may be used directly or directed onto a target to produce x-rays or fast neutrons. Particle accelerators are used to create radioactive materials for later administration to patients, mostly for diagnostic purposes, and to irradiate patients directly for treatment of malignancies. The accelerators may be betatrons, cyclotrons, linear accelerators, or synchrotrons, named for selected characteristics of their design.

Person-sievert,

or person-Sv, is a unit that represents the sum of the number of people exposed to radiation multiplied by their effective dose equivalent.

Photon

denotes a quantity of electromagnetic energy. Photons have no mass but do have momentum. Visible light, gamma rays, and x-rays are all photons.

Physical half-life

is the time required for half of a radioactive material to decay.

Physician

means a medical doctor or doctor of osteopathy licensed by a state or other authorities to prescribe drug treatments in the practice of medicine.

Positron

is a particle having a mass equal to that of the electron and a positive charge. The positron is anti-matter; when it interacts with an electron, they annihilate and photons are formed, which carry away the energy. The positron is also called a beta-plus particle, since it is like the beta-minus particle in origin. Positrons may be emitted in the radioactive decay process of radionuclides that contain excess protons; medically useful positron emitters include carbon-11, oxygen-13, nitrogen-15, and fluorine-18.

Positron emission tomography (PET)

is a tomographic technique in which detectors surround a patient who has been made radioactive with a positron-emitting radiopharmaceutical; the information from the detector is processed by the computer to create transaxial images of the distribution of the radiopharmaceutical within the patient.

Rad

is a unit of radiation absorbed dose. One rad is equal to 100 ergs deposited per gram of substance. The gray is the equivalent SI unit; 1 Gy = 100 rads.

Radiation oncology

is the study and treatment of malignant disease with radiation.

Radiation therapy

is the treatment of malignant disease with radiation. It is essentially a synonym for radiation oncology.

Radioactivity

means the spontaneous disintegration of a nucleus in which alpha, beta, or gamma radiation may be emitted.

Radioisotope—

see Isotope.

Radionuclide

means a nuclide that disintegrates, thus emitting radiation.

Radiopharmaceutical

is a pharmaceutical containing radioactivity. Radiopharmaceuticals may be made in a user's laboratory by combining radioactive materials with nonradioactive kits or by cyclotron production and subsequent formulation of materials with short half-lives; radiopharmaceuticals may also be purchased from commercial radiopharmacies or manufacturers.

Radiosensitivity

means that some cells are relatively more sensitive to radiation than others.

Recordable event

means, according to the NRC (10 CFR 35.2) an event that is less serious than a misadministration (see Misadministration ), but involving a dosage other than that prescribed of sodium iodide I-131 or I-125 or a therapeutic radiopharmaceutical, or of radiation from a brachytherapy or teletherapy treatment.

Rem

is a unit of dose equivalent. It is equal to the dose in rads multiplied by a quality factor for the particular type of radiation. The SI unit for dose equivalents is the sievert (Sv); 1 Sv = 100 rem.

Risk coefficient

is defined in terms of fatalities per person-Sv and allows a comparison between the risks of exposure to radiation and other risks.

Roentgen

is a unit of x- or gamma-radiation exposure such that absorption by 1 cubic centimeter of air produces an electrical charge of 1 electrostatic unit (esu). There is no SI equivalent to this unit, as its use is expected to disappear.

Roentgen equivalent man (rem)

is a unit of human biologic dose as a result of exposure to one or more types of ionizing radiation. It is equal to the absorbed dose in rads times the Relative Biological Effectiveness of the radiation in question.

Scanner

is a device used to detect x-rays or gamma radiation from a volume of tissue. The word is used in connection with nuclear medicine imaging and CT imaging. Originally it connoted a detector device that went back and forth to cover an area, but is now used colloquially for several kinds of instruments.

Scattering

is the loss of radiation from a beam by deflection by nuclei or electrons. Generally scattered radiation has a lower energy than the original beam.

Scintillation counter

combines an absorbing phosphor, a photomultiplier tube, a sample holder, and associated devices and circuits needed to count the light emissions created as the result of absorption of ionizing radiation in the phosphor. If the absorbing phosphor is liquid and the sample being counted

is dissolved in the liquid, the counter is a "liquid scintillation counter" and may detect beta and gamma rays.

Sealed source

means any radioactive material that is encased in a capsule designed to prevent leakage or escape of the contents; the NRC defines sealed sources in terms of encapsulated byproduct material.

Sievert

(Sv) is the SI unit for dose equivalent. It is equal to 100 rem.

Stable isotopes

are those isotopes of an element that do not disintegrate and are thus not radioactive. Stable isotopes may be used in magnetic resonance imaging or in tracer methods that use mass spectrometry for detection.

Stochastic—

see Nondeterministic.

Teletherapy

is radiation therapy by means of an external beam of radiation. The source is commonly a cobalt-60 irradiator or a linear or other accelerator.

Transmutation

means changing one element into another. This occurs in radioactive decay whenever a charged particle such as an alpha or beta particle is emitted.

Weighting factor

is a way of taking into account the particular anatomic area irradiated in a calculation involving the equivalent dose to the whole body. The weighting factor for an organ or tissue is the proportion of the risk of stochastic effects resulting from irradiation of that area to the total risk of stochastic effects when the whole body is irradiated. (See Committed effective dose equivalent.)

Worker or employee in the radiation industry

is an individual who may be exposed as a result of his or her occupation.

X-rays

are short-wavelength electromagnetic radiations (photons) that emanate from energy changes in electronic shells.

X-ray machines

are used in medicine for both diagnostic and therapeutic purposes. In an x-ray machine, a beam of x-rays is generated when a stream of electrons hits an anode target; the beam is directed by collimation toward the field to be irradiated. After being attenuated by passing through an object such as a patient, x-rays are detected by a screen–film combination inside a cassette or by a fluorescent screen in an image-intensifier tube. The screen–film combination yields a film for diagnosis by a physician; the image-intensifier tube signal is fed into a video system for immediate viewing, as in fluoroscopy. X-rays may be used therapeutically to treat cancer.