An eye tumor that is an example of an inherited malignant tumor with a dominant autosomal gene inheritance pattern.


A chance of injury, loss, or detriment; a measure of the deleterious effects that may be expected as the result of an action or inaction.

Risk assessment.

The process by which the risks associated with an action or inaction are identified and quantified.

Risk coefficient.

The increase in the annual incidence or mortality rate per unit dose: (1) absolute risk coefficient is the increase of the incidence or mortality rate per unit dose; (2) relative risk coefficient is the fractional increase above the baseline incidence or mortality rate per unit dose.

Risk estimate.

The increment of the incidence or mortality rate projected to occur in a specified exposed population per unit dose for a specified exposure regime and expression period.

Sievert (Sv).

Special name of the SI unit of dose equivalent (see Units). 1 Sv = 1 J/kg = 100 rem.

SI units.

Units of the International System of Units as defined by the General Conference of Weights and Measures in 1960. They are the base units, such as meter (m), kilogram (kg), second (s), and their combinations, which have special names (e.g., the unit of energy, 1 J = 1 kg m2/s2, or absorbed dose, 1 Gy = 1 J/kg = 1 m2/s2 (see Units).

Solid cancers.

Solid cancers include all malignant neoplasms other than those of the lymphatic and hematopoietic tissue.

Somatic cells.

Nonreproductive cells.

Specific activity.

Activity of a given nuclide per unit mass of a compound, element, or radioactive nuclide.

Specific energy (z).

The energy per unit mass actually deposited in a microscopic volume in a single energy deposition event or at a given absorbed dose. This is a stochastic quantity as opposed to its average, the absorbed dose, D. The mean energy imparted by ionizing radiation to a medium per unit mass. Unit: 1 Gy = 1 J/kg.

Standardized morbidity ratio or Standardized mortality rate (SMR).

The ratio (multiplied by 100) of the mortality rate from a disease in the population being studied divided by the comparable rate in a standard population. The ratio is similar to a relative risk times 100.


Effects whose probability of occurrence in an exposed population (rather than severity in an affected individual) depends on dose; stochastic effects are commonly regarded as having no threshold; hereditary effects are stochastic; some somatic effects, especially cancers, are regarded as being stochastic.

Suppressor gene.

A gene that can suppress another gene such as an oncogene. Changes in suppressor genes can lead to expression by genes such as oncogenes.

Synergistic effect.

Increased effectiveness results from an interaction between two agents, so that the total effect is greater than the sum of the effects of the two agents acting alone.

Target cells.

Cells in a tissue that have been determined to be the key cells in which changes occur in order to produce an end point such as cancer.

Threshold hypothesis.

The assumption that no radiation injury occurs below a specified dose.

Transformed cells.

Tissue culture cells changed from growing in an orderly pattern exhibiting contact inhibition to growing in a pattern more like that of cancer cells.


The range of values within which the true value is estimated to lie. It is a best estimate of possible inaccuracy due to both random and systemic errors.

Random Errors. Errors that vary in a nonreproducible way around a limiting mean. These errors can be treated statistically by use of the laws of probability.

Systemic Errors. Errors that are reproducible and tend to bias a result in one direction. Their causes can be assigned, at least in principle, and they can have constant and variable components. Generally, these errors cannot be treated statistically.

Units of dose.

Also known as dosimetric units.



Conversion Factors

Becquerel (SI)


1 disintegration/s = 2.7 × 10−11 Ci



3.7 × 1010 disintegrations/s = 3.7 × 1010 Bq

Gray (SI)


1 J/kg = 100 rad



0.01 Gy = 100 erg/g

Sievert (SI)


1 J/kg = 100 rem



0.01 Sv

aInternational Units are designated SI.

NOTE: Equivalent dose equals absorbed dose times Q (quality factor). Gray is the special name of the unit (J/kg) to be used with absorbed dose; sievert is the special name of the unit (J/kg) to be used with equivalent dose.

UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation).

A UN committee that publishes periodic reports on sources and effects of ionizing radiation.


The variation of a property or quantity among members of a population. Such variation is inherent in nature and is often assumed to be random; it can then be represented by a frequency distribution.

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