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Glossary
Absorbed dose. When ionizing radiation passes through matter, some of its en
- ergy is imparted to the matter. The amount absorbed per unit mass of
irradiated material is called the absorbed dose, and it is measured in gray or
red.
Aneuploid. A chromosome number that deviates from the normal for a species.
It may be more or less than the diploid chromosome number but it is not an
exact multiple of the basic haploid chromosome number found in germ
cells.
Autosome. Chromosomes other than the sex (X or Y) chromosomes. Humans
carry 22 pairs of autosomes.
lzospermia. Absence of sperm in a semen sample.
Background radiation. Radiation that is a natural part of a person's environ-
ment.
BEIR. Biological Effects of Ionizing Radiation. A series of reports by a com-
mittee of the National Academy of Sciences.
Beta particle. An electron with a positive or negative charge.
Carcinogenesis. The process of induction of cancer in a cell.
Case-control study. An epidemiologic investigation in which study subjects are
selected on the basis of having a disease or condition and are compared in
81
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82
ADVERSE REPRODUCTIVE OUTCOMES
terms of a particular exposure to individuals who are selected because they
do not have the condition. These studies are efficient for the study of rare
diseases with long latency periods, but they are particularly susceptible to
selection bias.
Chromosomes. Structural elements of various sizes in the cell nucleus com-
posed of deoxyribonucleic acid (DNA) and proteins, they carry the genes
that convey the genetic information of an organism. Chromosomes have a
species-specific morphology and number.
Clusters (of adverse reproductive outcomesJ. Aggregation of events in space and
time.
Cohort study. An epidemiologic investigation or follow-up of a group of indi-
viduals who are known to have had an exposure and are followed to see if
they develop a disease or condition. Usually cohort studies are expensive
and time-consuming because they typically follow a large number of indi-
viduals for many years.
Confidence Interval (CU. An interval within which a value for a population can
lie with calculable probability (the probability that the true answer lies
within the range). For example, an epidemiologic data point of 4.3 is sub-
ject to a number of uncertainties based on sample size and other factors.
The value should not be assumed to represent the "truth" but rather an ap-
proximation of it. If a 95% CI of (2.3 to 7.8) is given for the data presented,
this means that with repeated analysis of this data the result will fall
within this range 95% of the time.
Confounder. A variable that is causally related to the disease under study and is
associated with the exposure in the study population, but is not a conse-
quence of that exposure.
Congenital. Present at birth. Congenital does not imply either genetic or nonge-
netic causation.
Congenital malformation. Structural abnormality present at birth. This term is
often used interchangeably with birth defect.
Contamination (gradioactiveJ. A radioactive substance in a material or place
where it is undesirable.
Cosmic rays. Radiation of many sorts, but mostly atomic nuclei (protons) with
very high energies originating outside the earth's atmosphere. Cosmic ra-
diation is part of the natural background radiation. Some cosmic rays are
more energetic than any synthetic forms of radiation.
Criticality accident. An unintentional event during which nuclear fuel (e.g.,
uranium-235) configures to initiate a chain reaction, releasing radiation and
heat.
DDREF. A factor by which the effect caused by a specific dose of radiation
changes at low dose rates compared with that at high dose rates.
Decay (radioactiveJ. The spontaneous transformation of one nuclide (a nuclide
is any atomic form of an element) into a different nuclide or into a different
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GLOSSER Y
83
energy state of the same nuclide. The process results in a depletion, with
time, ofthe radioactive atoms in a sample. Radioactive decay involves (1)
the emission from the nucleus of alpha particles, beta particles (electrons),
or gamma rays; (2) the nuclear capture or ejection of orbital electrons; or
(3) fission. Also called radioactive disintegration. See Half-life.
Deformational. Subcategory of malformations in which the organ systems de-
velop normally, but they incur a secondary deformity, for example, midline
cleft palates.
Deletion. Loss of a portion of a chromosome as a result of chromosome break
age.
Deoxyribonucleic acid (DNAJ. The long double-stranded molecule whose se-
quence, which consists of the four nucleotide bases (adenine, thymine,
guanine, and cytosine), provides the genetic information of an organism.
DNA. See Deoxyribonucleic acid.
Dominant. A trait that is expressed in individuals who are heterozygous for a
particular gene.
Dose (radiation;. A term denoting the amount of energy absorbed. Absorbed
dose is the energy imparted to matter by ionizing radiation for each unit of
mass of irradiated material at the point of interest. It is usually expressed in
red (conventional units) or gray (international tSI] unit). Cumulative dose is
the total dose resulting from repeated or continuous exposures to radiation.
Dose equivalent (H). A unit of biologically effective dose, defined by the ICRP
in 1977 as the absorbed dose in reds multiplied by the quality factor (Q).
For all X rays, gamma rays, beta particles, and positrons likely to be used in
nuclear medicine, the quality factor is 1. The dose equivalent (H) is given
by the equation H = DQN, where D is absorbed dose, Q is the quality fac-
tor, and N is the product of modifying factors (N is usually 19. See also
Equivalent dose.
Dose rate (radiation,. The radiation dose delivered for each unit of time and
measured, for instance, in red per hour. See Absorbed dose.
Doubling dose. The dose of radiation that, under a given set of conditions, will
lead to an overall mutation frequency that is double the spontaneous fre
quency.
Down syndrome. A pattern of abnormalities related, in most cases, to the pres-
ence of an extra number 21 chromosome in all of the body's cells, giving
them 47 chromosomes instead of the usual 46. People with Down syn-
drome have various degrees of mental retardation and often have congenital
malformations of the heart.
DREF. see DDREF.
Effective dose. A quantity that takes into account the difference in sensitivity of
various body tissues and the effectiveness of different forms of radiation.
This quantity is used to obtain a uniform expression of risk for stochastic
effects. It was been defined by the ICRP in 1990 as the sum of equivalent
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ADVERSE REPRODUCTIVE OUTCOMES
doses that have been multiplied by a tissue weighting factor (WT). The unit
of effective dose is the sievert or rem.
Embryo. An organism in the first stages of development. In humans, this is gen-
erally considered to be the period from the end of the second week through
the eighth week of gestation.
Equivalent dose. A newer version of dose equivalent. It was defined by the
ICRP in 1990 and uses radiation weighting factors (WR) instead of the older
quality factor (Q).
Euploid. A chromosome number that is the exact multiple of the haploid chro
mosome number.
Excess relative risk (ERR9. Relative risk minus 1.
Exposure. A term relating, in this report, to the amount of ionizing radiation that
. . . . . .
Is ~nc~c ent on living or Inanimate material.
Exposure rate. Increment of exposure expressed for each unit of time.
F.. In this report, first generation conceived after exposure of parents.
Fecundab~lity. The ability to reproduce.
Fertility. The capacity to conceive or induce conception.
Fetus. Unborn offspring. In humans it is the period from 8 weeks after fertiliza-
tion until birth.
Film badge. Photographic film shielded from light. It is worn by an individual
to measure radiation exposure.
Gamete. A mature male or female germ cell (sperm or egg) containing a haploid
number of chromosomes.
Gamma ray. Electromagnetic radiation emitted from the nucleus.
Gene. The basic unit of heredity. A finite segment of DNA that controls the
production of a specific polypeptide.
Genetic code. The triplet sequence of nucleotide bases in the DNA chain, as
reflected in messenger ribonucleic acid (mRNA), that determines the se-
quence of amino acids during protein synthesis.
Genetic effects of radiation. Radiation effects that can be transferred from parent
to offspring. Any radiation-caused changes in the genetic material of germ
cells. Compare to somatic effects of radiation.
Genetically significant dose (GSDJ. The GSD is that dose (of radiation) which,
if received by every member of the population, would be expected to pro-
duce the same genetic injury to the population as that caused by the actual
doses received by the individuals irradiated. The GSD is expressed in
Sieverts (or rem).
Genotype. The genetic constitution of an individual that determines the physical
and chemical characteristics of that individual.
Germ cell. Refers to male and female reproductive cells at their various levels
of development (i.e., spermatogonia or oogonia, spermatocytes or oocytes
and spermatozoon or ovum).
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GLOSSER Y
Gray (Gy9. The international (SI) unit of radiation absorbed dose. One gray is
equal to an energy deposition of 1 joule per kilogram (100 red).
Half-life (radioactive9. The time required for a radioactive substance to lose
50% of its activity by decay.
Heterozygous. Having dissimilar alleles at the same locus on homologous chro
mosomes.
High dose. More than 2 Gy (200 red).
Homozygous. Having the same genes at a given locus on homologous chromo
somes.
ICRP. International Commission on Radiological Protection.
Incidence. The number of people who have developed a disease in a given pe-
riod of time divided by the total population at risk.
Induced burden. An increased number of genetic effects because of an expo
sure.
Intermediate dose. A dose of 0.2 to 2.0 Gy (20 to 200 red).
Ionization. The process whereby a charged portion (usually an electron) of an
atom or molecule is given enough kinetic energy to dissociate.
Ionizing radiation. Radiation that produces ion pairs along its path through a
substance.
Irradiation. Exposure to radiation.
Isotopes. Nuclides with the same numbers of protons but different numbers of
neutrons.
Klinefelter syndrome. A pattern of abnormalities related to the presence of an
extra sex chromosome. Persons with Klinefelter syndrome are males, but
they have 47 chromosomes, two X chromosomes and one Y chromosome,
instead of the usual male chromosomal makeup of 46 chromosomes, with
one X and one Y.
85
Latent period. Usually refers to the time elapsed between radiation exposure and
the clinical appearance of an effect (such as the appearance of a cancer).
LET. See Linear energy transfer.
Linear energy transfer (LETJ. Amount of energy lost by ionizing radiation by
way of interaction with matter for each unit of path length through the ab-
sorbing material.
Locus. The site occupied by a specific gene, or allele, on a particular chromo
some.
Low birth weight. A weight of less than 2,500 grams at birth.
Low dose. A dose of less than 0.2 Gy (20 red).
Low dose rate. Less than 0.1 mGy (100 mrad) per minute averaged over about 1
hour. It sometimes also refers to less than 10 mGy (1 red) per year.
Micro- (o. A prefix that divides a basic unit by 1 million.
Milli- (m). A prefix that divides a basic unit by 1,000.
Multifactorial. Refers to causation involving the interaction of a number of
factors, often including several genes and nongenetic (environmental) factors.
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AD VERSE REPRODUCTIVE OUTCOMES
Mutation. A hereditary change in genetic material. A mutation can be a change
in a single gene (point mutation) or a change in the order or number genes.
Mutation rate. The rate at which mutations occur at a given locus, expressed as
the number of mutations per gamete for each locus in a generation.
NCRP. National Council on Radiation Protection and Measurements.
Nuclear Regulatory Commission (NRC). A U.S. government agency regulating
by-product material.
Nucleus (atomJ. The small, positively charged core of an atom. It is only about
1/lO,OOOth ofthe diameter of the atom, but, it contains nearly all ofthe
atom's mass. All nuclei, except the nucleus of ordinary hydrogen, contain
both protons and neutrons, the nucleus of ordinary hydrogen, consists of a
single proton.
Nucleus (cell9. A mass of protoplasm within the cytoplasm of a cell. It is sur-
rounded by a membrane and contains substances that direct the cell's me
tabolism, growth, and reproduction.
Nuclides. A general term applicable to all atomic forms of an element. The term
is often used incorrectly as a synonym for isotope, which properly has a
more limited definition. Whereas isotopes are the various forms of a single
element (hence, are a family of nuclides) and all have the same atomic
number and number of protons, nuclides comprise all of the isotopic forms
of all of the elements. Nuclides are distinguished by their atomic number,
atomic mass, and energy state.
Odds ratio (OR). Used as an estimation of relative risk. It is primarily used for
case-control studies and is calculated from the odds of exposure among the
cases to that among controls.
Oligospermic. A reduced sperm count; it has various in definitions but often
refers to a count of less than 20 million sperm per milliliter of semen.
P'~~1^w~rloi~ ~`r~prtpncirin inrillr~1 hv nreannnc.v nfl~.r 9() weeks of gestation
1 I GAG-at-Aim.. ~ $~ Eve ·_A1~ AA-~__~ ~9 id, _=A^~A^_J ~
that is accompanied by proteinuria, edema or both.
Preterm birth. A birth that occurs at a gestational age of less than 37 completed
weeks (~259 days).
Prevalence. The proportion of individuals in a population who have a disease at
a specific time, for example, the number of people in the United States who
have lung cancer. It is not the number of new cases in that year. Prevalence
is the incidence multiplied by the average duration of disease.
Quality factor. (QF). Dependent factor by which absorbed doses are to be mul-
tiplied to account for the various degrees of effectiveness of different
radiations. QF for 250-kVp X rays is equal to 1. See also Weighting factor
(radiation).
Rad. Radiation absorbed dose. A unit of absorbed dose of ionizing radiation.
One red is equal to 100 ergs/g. See Gray.
Radiation. Energy propagated through space or matter as waves (gamma rays,
ultraviolet light) or as particles (alpha or beta particles). External radiation
OCR for page 87
GLOSSAR Y
87
is from a source outside the body, whereas internal radiation is from a
source inside the body (such as radionuclides deposited in tissues).
Radiation therapy. Treatment of disease with any type of radiation. Often called
radiotherapy.
Radioactivity. The property of some nuclides of spontaneously emitting
radiation.
Radionuclide. Unstable nucleus that transmutes by way of nuclear decay.
Radiosensitivity. A relative susceptibility of cells, tissues, organs, or organisms
to the harmful action of radiation.
Recessive. Refers to a gene that produces its effect (is expressed) only when it is
present in the homozygous or hemizygous state.
Relative risk (RIB. The ratio of the disease incidence in the exposed population
divided by the incidence in the nonexposed population. If there is no differ
ence as a result of exposure, the RR is 1.0. A relative risk of 1.1 indicates a
10% increase in the number of cases than would be expected.
Rem. See Roentgen equivalent man.
Risk, absolute. In this report, the excess risk attributed to irradiation and usually
expressed as the numeric difference between irradiated and nonirradiated
populations (e.g., one excess case of cancer/1 million people irradiated an
nually for each red). Absolute risk may be given on an annual or lifetime
(70-year) basis.
Roentgen (R9. Quantity of X- or gamma-ray radiation per cubic centimeter of
air that produces one electrostatic unit of charge.
Roentgen equivalent man (rem9. The unit of the biologically effective dose. The
absorbed dose in red multiplied by the quality factor of the type of radia
tion. See Sievert.
Sex chromosomes. Chromosomes that determine the sex of the individual: in
humans, the X chromosome in the female, the X and Y chromosomes in the
male.
Sex-linked gene. A gene located on a sex chromosome. Often used to describe
genes on the X chromosome, although X-linked is the more accurate term.
Sievert (SvJ. The international (SI) unit of dose equivalent. The absorbed dose in
gray multiplied by the quality factor or radiation weighting factor of the
type of radiation. One sievert equals 100 rem.
Somatic cells. All cells in the body except gametes and their precursors.
Somatic effects of radiation. Effects of radiation that are limited to the exposed
individual, as distinguished from genetic effects, which only affect subse-
quent unexposed generations. Large radiation doses can cause somatic ef-
fects that are fatal. Lower doses may make the individual noticeably ill,
may produce temporary changes in blood cell levels detectable only in the
laboratory, or may have no detectable effect.
Somatic mutation. A mutation occurring in a somatic cell (i.e., one that is not
passed on to future generations).
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AD VERSE REPRODUCTIVE OUTCOMES
Spontaneous abortion. Non-deliberate interruption of intra-uterine pregnancy
before 28 of weeks gestation in which the embryo or fetus is dead when
delivered.
Stillbirth. Fetal death at 28 weeks of gestation or later (from last menstrual pe-
riod).
Stochastic elect. An effect whose probability of occurrence in an irradiated
population or individual is a function of dose. Commonly regarded as hav-
ing no threshold dose. An example is radiation carcinogenesis.
Teratogenic. Related to the induction of structural malformations in an embryo
and fetus.
Teratogens. Agents that can cause structural malformations in the developing
embryo or fetus.
Threshold dose. The minimum dose of radiation that will produce a detectable
biologic effect.
\
Tissue weightingiactor. See weighting factor.
Toxicant. The actions and effects of a toxicant are similar to those of a toxin,
but the source is a synthetic or artificial substance rather than a natural one.
Toxin. A natural substance that can induce a poisonous effect.
Translocation. The transfer of genetic material from one chromosome to an
other, nonhomologous chromosome. An exchange of genetic material be
tween two chromosomes, each of which retains a centromere, is referred to
as a reciprocal translocation. When a small fragment, which is usually lost,
Is formed (centric fusion), this is referred to as a Robertsonian translocation.
Triplet. In molecular genetics, a unit of three successive bases in DNA or RNA,
coding for a specific amino acid.
Trisomy. A state in which there are three members of a given chromosome in
stead of the normal pair.
Turner syndrome. A pattern of abnormalities related to the absence of a sex
chromosome. People with Turner syndrome have 45 chromosomes rather
than the usual number of 46 and are female. They have a single X chromo-
some, and the syndrome is often referred to as XO Turner syndrome.
UNSCEAR. United Nations Scientific Committee on the Effects of Atomic Ra-
diation. A series of reports by a committee of the United Nations.
Weightingfactor (WTJ. A number of values that are used to adjust for the various
sensitivities of tissues and effectiveness of radiations in order to express
risk. The values listed here were derived by the International Commission
on Radiological Protection in 1990 and refer to stochastic effects only.
Weightingiactor (radiations
photons
electrons and muons
neutrons
protons
alpha particles
1.0
1.0
5-20 (the value depends upon the energy)
5.0
20.0
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GLOSSAR Y
Weightingiactors (tissue)
bone
skin
bladder
breast
liver
0.01
0.01
0.05
0.05
0.05
esophagus 0.05
thyroid 0.05
remaining organs 0.05
bone marrow 0.12
colon 0.12
lung 0.1 2
stomach 0.12
gonads 0.20
X chromosomes. A sex chromosome found in duplicate in the normal female
and singly in the normal male.
X-linked. Genes carried on the X chromosome.
Y chromosome. One of the sex chromosomes found in the normal male. The Y
chromosome is essential for the development of male gonads.
89
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Representative terms from entire chapter:
ionizing radiation
