Cell-killing effect:

The cessation of cell division and/or metabolism. Sufficient doses of radiation may kill cells in the body. Cell death is responsible for most of the acute effects of radiation.

Cell sensitivity to radiation:

The relative sensitivity (radiosensitivity) of individual cell types to the cell-killing or mutagenic effects of radiation.

Cell transformation:

A process by which cells in vitro, which have a limited ability to divide, are altered by radiation or chemicals so as to have an unlimited division potential. (See Neoplastically transformed cells.)


A unit of radioactivity equal to 3.7 × 1010 disintegrations per second.

Deterministic effects:

Effects formerly known as nonstochastic effects that may appear early or late after irradiation. There is a threshold dose above which both the probability of occurrence and the severity of the effect increase. Most deterministic effects involve cell killing.


See Absorbed dose.

Dose effect (dose response) model:

A mathematical formulation used to predict the magnitude of an effect that would be produced by a given dose of radiation.

Dose equivalent:

See Equivalent Dose.

Dose rate:

The quantity of absorbed dose delivered per unit of time.

Doubling dose:

Amount of radiation needed to double the natural incidence of a genetic or somatic abnormality.


A factor by which the effect caused by a specific dose of radiation changes at low dose rates as compared with high dose rates.

Electron volt:

A unit of energy (1.6 × 10-19 J). 1 eV is equivalent to the amount of energy gained by an electron passing through a potential difference of 1 volt.

Epidemiologic study:

The study of human populations designed to establish the relationships among various factors that determine the frequency and distribution of a disease. For example, a number of such studies have examined the role of radiation (the factor) in the induction of cancer (the disease). The science of epidemiology is derived from the word “epidemic.”


Loss of hair.

Equivalent dose:

Absorbed dose averaged over an organ or tissue and weighted for the radiation quality for the type of radiation of concern.


Redness of the skin. A transient erythema can occur a few hours after irradiation due to increased permeability of the capillaries. The main erythematous reaction occurs some weeks after exposure to radiation and is due to loss of cells in the basal layer. A late phase 8 to 20 weeks after irradiation is associated with damage to the dermis.

Excess cancers:

The number of individuals in a population who develop cancer over and above the number that would be expected to do so normally. Normally, about one out of every four people will develop cancer during his or her lifetime, and cancer will strike two out of every three families.


The delivery of a given total dose of a radiation as several smaller doses, separated by intervals of time.

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