Affinity: ability of a substance to bind to a receptor; it is a measurement of the strength of the binding.
ALARA: As Low As Reasonably Achievable. Radiation protection policy related to the management of staff working in an ionizing radiation environment.
Alpha (α) (alpha radiation): a particle emitted by a radioisotope and formed from a nucleus of helium containing two protons and two neutrons with potential therapeutic uses owing to strong ionizing power.
Becquerel (Bq): unit of radioactivity equal to one (1) disintegration per second. The becquerel replaces the former curie unit, one curie being the equivalent of 37 billion becquerels.
Beta-minus (β-) (beta-minus radiation): a particle emitted by a radioisotope and formed from a negatively charged electron, usable in therapy owing to its destructive potential.
Beta-plus (β+) (beta-plus radiation): a particle emitted by a radioisotope and formed from a positively charged electron (positron), an unstable anti-electron, which when it meets a negatively charged electron is annihilated to emit two gamma photons that move in exactly opposite directions and are therefore usable in imaging.
Biological half-life: time period at the end of which a cell or tissue has eliminated half the quantity of a molecule present by a biological metabolic mechanism followed by excretion.
Brachytherapy: method of internal irradiation by the temporary or permanent introduction of radioactive implants. Examples: radioactive seeds marked with iodine-125 in prostate tumors, iridium wires in breast tumors, and phosphorus-32 patches.
Cold kit: non-radioactive precursor of a radiopharmaceutical containing all the elements that enable this medication to be reconstituted almost instantaneously, simply by adding a radionuclide solution.
Computerized tomography (CT): cross-sectional imaging (usually with X-rays) allowing three-dimensional reconstruction.
Contamination: physical contact leaving a deposit of radioactive material on a surface, matter, or person. The contaminated person is irradiated as long as the active matter has not been eliminated or the radioactivity has not fully decayed naturally.
CT: abbreviation of computerized tomography.
Curie (Ci): unit of radioactivity; one curie equates to the radioactivity emitted by one gram of pure radium-226, one of the first natural radioactive materials available and isolated at the beginning of the last century. In principle, this unit should no longer be used because it was replaced by the becquerel (see entry for this word) in the 1980s.
Curietherapy: see Internal radiotherapy.
Decay: reduction in the degree of radioactivity over the course of time.
Dosimetry: the study and measurement of absorbed radiation.
Effective dose: the equivalent dose corrected by the weighting coefficient relating to the irradiated tissue (0.05 for the thyroid, 1 for the whole body) expressed in sieverts.
Effective half-life: radioactive half-life corrected by the biological half-life. With this information, the practitioner can estimate how long a radioactive substance that has been ingested by or injected into a patient will take before generating an effect on the organism (or a certain type of cell or tissue).
EMEA: European Medicines Evaluation Agency, European Health Authority: decentralised agency of the European Union, located in London. Recently renamed as EMA: European Medicines Agency
Equivalent dose or Dose equivalent: absorbed dose corrected by a weighting coefficient relating to the radiation (1 for X-rays, β-rays, and γ-rays, 20 for α-rays), expressed in sieverts. This is a value used in radiation protection to take account of the difference in biological effect of the various types of radiation.
External radiotherapy: method of therapy by irradiation using a source external to the patient (former cobalt therapy, but now X-ray therapeutic beams and also neutron therapy or proton therapy). Domain of the radiotherapist.
FDA: Food and Drug Administration, American Health Authority.
FDG (Fluorodeoxyglucose): substance labeled with fluorine-18, most frequently used for diagnosis based on positron emission tomography technology. A radiolabeled glucose analog that allows glucose-consuming cells such as tumor cells to be displayed.
Free radical: an extremely reactive chemical entity which contains a redundant electron and which is at the origin of later chemical transformations.
Galenic: study of the method of administering a medication.
Gamma (γ): radiation of a shorter wavelength than X-rays emitted by certain radionuclides and with very high energy; usable for diagnostic imaging.
Generator: tool for the production of a radioisotope by the decay of a parent radionuclide from which it is regularly separated by a physical means (column filtration, extraction).
GMP: Good Manufacturing Practice, the present highest industry standards for drug production. GLP stands for Good Laboratory Practice (Research) and GCP for Good Clinical Practice (Clinical Research and Development).
Gray (Gy): unit of absorbed dose corresponding to one joule per kilogram. The former unit of absorbed dose is the rad, with one gray equaling 100 rads.
Half-life: radioactive half-life, see Radioactive half-life. The term biological half-life is also used, which corresponds to the time at the end of which half the quantity of a substance has disappeared or been eliminated from a cell by a biological process.
Incidence: Number of new cases of a disease appearing during a certain period of time (usually one year).
IND: Investigational New Drug (dossier) – dossier containing all data gathered so far and required to obtain the authorization to perform a clinical trial.
Internal radiotherapy: method of therapy by irradiation using a sealed radioactive source inserted into a natural cavity or implanted, temporarily or permanently, into the tissues. Synonym for curietherapy. Domain of the radiotherapist.
Intracavity radiation: the emission of rays from a source placed inside a cavity: uterus, throat.
Intraoperative radiation: irradiation during a surgical operation.
Ionizing (radiation): electromagnetic or corpuscular radiation capable of producing ions (positively or negatively charged atoms or molecules) directly or indirectly during its passage through matter. This transformation of the molecules is considered to be destructive and induces a biological change. X-, β+-, and γ-rays are considered weak ionizers compared with β-- and above all with α-rays.
Irradiation: exposure to radiation, without physical contact with the radioactive material; not to be confused with contamination in which there is a transfer of radioactive material. Once outside the radioactive field, the person is no longer exposed to the effects of the radiation.
Isotope: All the atoms, the nuclei of which have the same number of protons, form a chemical element. There are 92 natural elements, to which 17 known artificial elements must be added. When a given number of protons are associated in an atom with different numbers of neutrons, they represent variant chemical elements called isotopes. In most cases only a few forms are stable; the other unstable forms are called radioisotopes or radionuclides. Of the 109 currently known elements, 28 exist only in an unstable, that is to say radioactive, form. This is the case for uranium, plutonium, and radium. There are more than 3,000 known radionuclides.
Label: an entity (simple or complex) which, due to its radiation or its color, can be monitored in a complex biological system.
Labeling: method of chemical fixation of a radioisotope on a non-radioactive molecule.
Ligand: part of the molecule joining the vector to the central radioactive atom and which can also confer particular properties on the whole, such as better solubility or better ability to be absorbed by cells.
Metabolic radiotherapy: method of therapy by selective irradiation of a target zone by a molecule participating in the metabolism and labeled with a radioisotope, injected into the patient. Domain of the nuclear physician.
MRI: magnetic resonance imaging; another name for medical nuclear magnetic resonance.
NDA: New Drug Application – dossier containing all data generated during the development of a drug that has to be filed in order to obtain a Marketing Authorization.
Neutron: a neutral elementary particle (with no electrical charge), a constituent of the nucleus of the atom together with the proton.
Neutron therapy: external radiotherapy using a neutron beam.
Nuclide: atomic nucleus.
Oncology (or cancerology): medical science covering the field of prevention, detection, and treatment of cancers.
Orphan drug: substance that has been developed for a disease that is rare, an orphan disease, that would not be considered a high priority by industry without incentives. Depending on the country, a disease can be considered as an orphan if it affects less than 5 out of 10,000 individuals in the population.
PET: positron emission tomography. Imaging modality based on the detection of the two gamma photons generated by a positron emitter.
PET/CT: imaging technology combining positron emission tomography and X-ray analysis.
Positron: see Beta-plus.
Posology: dosage and procedures for administering a medicine.
Prevalence: total number of patients at a given time for a defined disease. It is an estimation of how common a disease is in a population.
Proton: a positively charged elementary particle, constituting the nucleus of the atom together with the neutron.
Proton therapy: method of external radiotherapy using a proton beam.
Rad: see Gray.
Radiation: a beam of invisible particles or waves emitted by a source. Also, it corresponds to the process of transmission of energy in corpuscular (α, β- particles, etc.) or electromagnetic form (visible light, ultraviolet, infrared, X, γ, etc.)
Radioactive half-life (or period): time at the end of which half the atoms initially present in a radioactive element have disappeared through spontaneous transformation. This period (half-life) is different for each radionuclide, but is a precise physical constant for a given radionuclide and is influenced by neither temperature nor pressure.
Radioactivity: property of certain radionuclides which emit particles spontaneously (electrons, protons, neutrons, nuclei) and/or α-, β-, γ-, or X-rays.
Radiochemical: a radioactive substance not intended for human use.
Radiochemist: a chemist specializing in the manufacture of radioactive substances; therefore, in the field of nuclear medicine, a specialist in the development of labeling, and in the field of nuclear physics, a specialist in the chemistry of radionuclides.
Radiochemistry: chemistry of substances incorporating a radioactive element.
Radioelement: an element where all the isotopes are radioactive, e.g., those of the plutonium or uranium groups (term often used wrongly in the place of radionuclide or radioisotope).
Radioisotope: an unstable isotope that decays over the course of time, emitting radiation (see Radionuclide).
Radiologist: specialist in X-ray imaging.
Radionuclide: radioactive atomic nucleus. Two radionuclides compared with each other are called radioisotopes if they belong to the same family of atoms (e.g. the radioisotopes of iodine, such as iodine-123, -124, or -131) and radionuclides in other cases. The word in the plural, ‘radioisotopes,’ is frequently used wrongly to designate all radionuclides.
Radiopharmaceutical: radioactive medication intended for diagnosis or therapy in the field of nuclear medicine.
Radiopharmacist: a hospital pharmacist specializing in the labeling and handling of radiopharmaceutical preparations intended for administration to a patient.
Radiopharmacy: a laboratory, principally located in a hospital, equipped to handle radioactive substances for injection into patients.
Radiophysician: physician specializing in the handling and production of radionuclides.
Radiotherapist: physician specializing in treatment by external radiotherapy. If the radioactive substance has to be injected into a patient, this task is entrusted to the nuclear physician.
Radiotherapy: method of therapy (treatment of a disease) based on the use of radiation, of whatever sort (X-, α-, or β-rays, neutrons, etc.).
Rem: see Sievert.
Scanner: an imaging tool using X- or γ-rays that provide virtual sectioning (scans) of the area being analyzed.
Scintigraphy: method of imaging based on recording γ or β+ radiation emitted by a substance injected into the patient which concentrates in a particular organ or tissue (heart, thyroid, bones, etc.).
Sealed source: a radioactive substance placed in a sealed container, irradiating but not contaminating. The implants used in internal radiotherapy are sealed sources.
Side-effects or undesirable effects: disturbance to the state of health of any sort not linked to the principal illness, but more often to the treatment itself. For example: headaches, gastric problems, nausea and vomiting, hair loss, and changes in blood count as a result of, or in parallel to, chemotherapy.
Sievert (Sv): unit of equivalent dose, corresponding to a corrected dose of the ionizing effect of the radiation (for X, β+, and γ radiation, 1 Sv = 1 Gy). Previously the rem was used, with one sievert equivalent to 100 rems.
Source: origin of radiation. By extension, the radioactive substance itself.
Specific activity: radioactive activity value comparing the activity of the radionuclide with the total mass of the element present. When the radioisotope is present in its pure form, even in an extremely dilute solution, we talk about a carrier-free radioisotope solution. It is expressed in becquerels per mass unit.
Specific concentration: value that determines the degree of radioactive substance per volume unit. It is expressed in becquerels per volume unit.
Specific/specificity: describes molecules that only target a single type of cell or receptor.
SPECT: single-photon emission computed tomography. The imaging modality based on the measurement of γ-ray emission.
Targeted or vectorized radiotherapy: a more general term including metabolic radiotherapy. This nuclear medicine technique consists in treating a specific tissue of the organism with ionizing radiation, itself originating from the concentration of a substance which participates in a biological mechanism (the vector) and to which a suitable radionuclide is grafted.
Tomography: radiography providing a clear image of a single cross-section.
Vector: chemical substance which has the property of being recognized by certain macromolecules present in tissue (receptor, enzyme, etc.) and on which is grafted another toxic or radioactive substance, for therapeutic or diagnostic purposes.
X-rays: invisible, short-wave, light radiation, produced by a radioactive substance and capable of crossing material.
