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130 terms

Biological aspects of radiation

STUDY
PLAY
During the 2nd to 10th week of pregnancy
time of major organogenesis; fetal anomalies can be produced. Skeletal and/or organ anomalies can appear if irradiation occurs early on, and neurologic anomalies can be formed in the latter part; mental retardation childhood malignant diseases can also result from irradiation during the first trimester
Fetal irradiation during the second and third trimester
with sufficient dose, can cause some type of childhood malignant disease
Fetal irradiation during the first 2 weeks of gestation
will most likely result in embryonic resorption or spontaneous abortion
How do fractionation and protraction affect radiation dose-effects?
1. They reduce the effect of radiation exposure.
2. They permit cellular repair.
3. They allow tissue recovery.
Fractionation and protraction
influence the effect of radiation on tissue. Larger quantities increase tissue effect.energy (quality, penetration) o radiation determines whether effects will be superficial (erythema) or deep (organ dose). Certain tissues (such as blood-forming organs, the lens, and the gonads) are more radiosensitive than others (such as muscle and nerve). If the dose is delivered in portions (fractionation), and/or delivered over a length of time (protraction), the less the tissue effects.
natural background radiation
is a result of cosmic radiation from space, naturally radioactive elements within the earth's crust (terrestrial) and our own bodies (internal radionuclides). the closer we are to the cosmic radiations from space, the greater our personal exposure will be; living at higher elevations and air travel expose us to greater amounts of radiation. Living or working in a building made of materials derived from the ground exposes us to some background radiation from the naturally radioactive elements found in the earth's crust. The food we eat, the water we drink, and the air we breathe, all contribute to the quantity of radiation we ingest and inhale
Man-made radiation
type of background radiation over which we have some control. Medical and dental x-rays, and nuclear medicine, contribute to our exposure to man-made background radiation
Which of the following accounts for the x-ray beam's heterogeneity?
1. Incident electrons interacting with several layers of tungsten target atoms
2. Energy differences among incident electrons
3. Electrons moving to fill different shell vacancies
Bremsstrahlung (or Brems) radiation
is one of the two kinds of x-rays produced at the tungsten target of the x-ray tube. The incident high-speed electron, passing through a tungsten atom, is attracted by the positively charged nucleus and therefore is deflected from its course, with a resulting loss of energy. This energy loss is given up in the form of an x-ray photon
The dose-response curve that appears to be valid for genetic and some somatic effects is the
linear nonthreshold
The x-ray interaction with matter that is responsible for the majority of scattered radiation reaching the IR is
Compton scatter
gestation
The length of time from conception to birth; pregnancy
congenital
refers to a condition existing at birth
Neonatal
relates to the time immediately after birth and the first month of life
In vitro
refers to something living outside a living body (as in a test tube)
in vivo
within a living system
Stochastic effects of radiation are those that
1. may be described as "all-or-nothing" effects.
2. are late effects.
What is used to account for the differences in ionizing characteristics of various radiations, when determining their effect on biologic material?
Radiation weighting factors (Wr)
In radiation protection, the product of absorbed dose and the correct modifying factor (rad x QF) is used to determine
rem (Sv)
Rem (dose-equivalent) is the only unit of measurement that expresses the dose-effect relationship. The product of rad (absorbed dose) and the quality factor appropriate for the radiation type is expressed as rem or DE (dose equivalent), and may be used to predict the type and extent of response to radiation
Immature cells are referred to as
1. undifferentiated cells.
2. stem cells.
Neurons and neuroglia
composed of nondividing, differentiated cells
Late or long-term effects of radiation exposure are generally represented by which of the following dose-response curves?
Linear nonthreshold
The most radiosensitive portion of the GI tract
the small bowel; projecting from the lining of the small bowel are villi, from the crypts of Lieberkühich are responsible for the absorption of nutrients into the bloodstream. Because the cells of the villi are continually being cast off, new cells must continually arise from the crypts of Lieberküeing highly mitotic, undifferentiated stem cells, they are very radiosensitive
tissues into order from lowest weighting factor (Wt) to highest weighting factor.
(A) Skin
(B) Breast
(C) Lung
(D) Bone marrow
Sources of natural background radiation contributing to whole-body radiation dose include
1. terrestrial radionuclides.
2. internal radionuclides.
Which of the following radiation exposure responses exhibit a nonlinear threshold dose-response relationship?
1. Skin erythema
2. Hematologic depression
3. Lethality
The genetic effects of radiation and some somatic effects, like leukemia, are plotted on
a linear dose-response curve.
The linear dose-response curve has
no threshold; that is, there is no dose below which radiation is absolutely safe.
The nonlinear/sigmoidal dose-response curve has a
threshold and is thought to be generally correct for most somatic effects—such as skin erythema, hematologic depression, and radiation lethality (death).
photoelectric effect
inner shell electron
Compton scatter
outer shell electron
classical scatter,
a low-energy photon interacts with an atom but causes no ionization; the incident photon disappears into the atom, and is then immediately released as a photon of identical energy but changed direction.
Thompson scatter
another name for classical scatter.
LET
increases with the ionizing potential of the radiation, for example, alpha particles are more ionizing than x-radiation; therefore, they have a higher LET.
As ionizations and LET increase,
there is greater possibility of an effect on living tissue; therefore, the RBE increases
RBE
(sometimes called QF—Quality Factor) of diagnostic x-rays is 1; the RBE of fast neutrons is 10; the RBE of 5 MeV alpha particles is 20.
Biologic material irradiated under hypoxic conditions is
less sensitive than when irradiated under oxygenated conditions
Myocytes
mature muscle cells and are fairly radioresistant.
radiosensitivity
red blood cell precursors, or erythroblasts, are the most radiosensitive. White blood cell precursors, or myelocytes, follow. Platelet precursor cells, or megakaryocytes, are even less radiosensitive.
Which of the following is (are) possible long-term somatic effects of radiation exposure?
1. Carcinogenesis
2. Leukemia
Somatic effects
are those induced in the irradiated body
Genetic effects
of ionizing radiation are those that may not appear for many years (generations) following exposure.
long-term somatic effects of radiation exposure
Formation of cataracts or cancer (such as leukemia), embryologic damage, and life-span shortening.
early effects of exposure to large quantities of ionizing radiation
Nausea and vomiting
The photoelectric effect is the interaction between x-ray photons and matter that is largely responsible for patient dose. The photoelectric effect is likely to occur under which of the following conditions?
1. With absorbers of high atomic number
2. With low-energy incident photons
3. With the use of positive contrast media
Dry desquamation
a dry peeling of the skin
Moist desquamation
is peeling with associated puslike fluid.
Which of the following factors can affect the amount or the nature of radiation damage to biologic tissue?
1. Radiation quality
2. Absorbed dose
3. Size of irradiated area
Radiation quality
determines degree of penetration and the amount of energy transferred to the irradiated tissue (LET)
The nature of the effect is influenced by
the location of irradiated tissue (bone marrow vs gonads and so on).
What is used to account for the differences in ionizing characteristics of various radiations, when determining their effect on biologic material?
1. Radiation weighting factors (Wr)
Tissue Weighting Factor (Wt)
represents the relative tissue radiosensitivity of irradiated material (eg, muscle vs intestinal epithelium vs bone, etc).
Radiation Weighting Factor (Wr)
a number assigned to different types of ionizing radiations in order to better determine their effect on tissue (eg, x-ray vs alpha particles).
Wr of different ionizing radiations is dependent on
the LET of that particular radiation.
Effective Dose (E)
= Radiation Weighting Factor (Wr ) x Tissue Weighting Factor (Wt ) x Absorbed Dose
The dose of radiation that will cause a noticeable skin reaction is referred to as the
skin erythema dose (SED)
The effects of radiation exposure to the skin follow a
nonlinear, threshold dose-response relationship
An individual's response to skin irradiation depends on
the dose received, the period of time over which it was received, the size of the area irradiated, and the individual's sensitivity
Which type of dose-response relationship expresses radiation-induced leukemia?
Linear, nonthreshold
Radiation-induced malignancy, leukemia, and genetic effects are
late effects (or stochastic effects) of radiation exposure
stochastic effects
can occur years after survival of an acute radiation dose, or after exposure to low levels of radiation over a long period of time
Radiation workers need to be especially aware of
the late effects of radiation because their exposure to radiation is usually low-level over a long period of time.
Occupational radiation protection guidelines are based on
late effects of radiation according to a linear, nonthreshold dose-response curve.
The tissue weighting factor of
gonads is 0.20
bone marrow, colon, lung, and stomach is 0.12
bladder, breast, esophagus, liver, and thyroid have a tissue weighting factor of 0.05
skin and surface of bone weighting factor is 0.01.
tissue weighting factor (Wt )
represents the relative tissue radiosensitivity of irradiated material (e.g., muscle versus intestinal epithelium versus bone, etc.).
radiation weighting factor (Wr )
a number assigned to different types of ionizing radiations in order to better determine their effect on tissue (e.g., x-rays versus alpha particles).
Wr of different ionizing radiations depends on
the LET of that particular radiation
radiation weighting factor of
x and gamma radiation, as well as electrons, is 1
protons is 2
alpha particles is 20
neutrons can be anywhere between 5 and 20 depending on their energy.
The following formula is used to determine effective dose (E):
E = Wr x Wt x absorbed dose
In the production of Bremsstrahlung radiation, the incident electron
is deflected, with resulting energy loss
Bremsstrahlung (or Brems) radiation
is one of the two kinds of x-rays produced at the tungsten target of the x-ray tube; The incident high-speed electron, passing through a tungsten atom, is attracted by the positively charged nucleus and therefore is deflected from its course, with a resulting loss of energy. This energy loss is given up in the form of an x-ray photon.
Early symptoms of acute radiation syndrome include
1. leukopenia.
2. nausea and vomiting.
acute radiation syndrome
whole body receives 600 rad at one time
Early signs of acute radiation syndrome include
nausea, vomiting, diarrhea, fatigue, and leukopenia (decreased white blood cells count); these occur in the first (prodromal) stage of acute radiation syndrome.
most radiosensitive to least radiosensitive:
(A) Immature spermatogonia
(B) Osteoblasts
(C) Epithelial cells
(D) Muscle cells
If 600 rad or more is received as a whole-body dose in a short period of time, certain symptoms will occur; these are referred to as
acute radiation syndrome
When 600 rad or more is received as a whole-body dose in a short time, biologic effects will appear within
minutes to weeks (depending on the dose received).
What is used to account for the differences in tissue sensitivity to ionizing radiation when determining effective dose (E)?
Tissue weighting factors (Wt)
The effects of a quantity of radiation delivered to a body is dependent on a few factors, including
the amount of radiation received, the size of the irradiated area, and how the radiation is delivered in time.
Late or long-term effects of radiation exposure are generally represented by which of the following dose-response curves?
Linear nonthreshold
Late or long-term effects of radiation can occur in tissues that have
survived a previous irradiation months or years earlier
late effects
such as carcinogenesis and genetic effects, are "all-or-nothing" effects—either the organism develops cancer or it does not.
Most late effects
do not have a threshold dose; that is, any dose, however small, theoretically can induce an effect. Increasing that dose will increase the likelihood of the occurrence, but will not affect its severity; these effects are termed stochastic.
Nonstochastic effects
those that will not occur below a particular threshold dose and that increase in severity as the dose increases.
straight (linear) line, indicates
response is proportional to dose. That is, as dose increases, response increases.
nonlinear
a response initially occurs slowly, then increases sharply as exposure increases
LET is best defined as
1. a method of expressing radiation quality.
2. a measure of the rate at which radiation energy is transferred to soft tissue.
What is (are) the major effect(s) of deoxyribonucleic acid (DNA) irradiation?
1. Malignant disease
2. Chromosome aberration
3. Cell death
If the damage happens to the DNA of a germ cell, the radiation response may not occur until
one or more generations later
Diagnostic x-radiation may be correctly described as
low energy, low LET
X-radiation used for diagnostic purposes is of relatively low
energy
Isotopes are atoms that have the same
atomic number but a different mass number; They differ in the number of neutrons
isobars.
Atoms with the same mass number but different atomic number
isotones
Atoms with the same number of neutrons but different atomic number
isomers
Atoms with the same atomic number and mass number
Which of the following ionizing radiations is described as having an RBE of 1.0?
Diagnostic x-rays
RBE
(sometimes called QF—Quality Factor) of diagnostic x-rays is 1; the RBE of fast neutrons is 10; the RBE of 5 MeV alpha particles is 20, and the RBE of 10 MeV protons is 5.0.
The genetic effects of radiation and some somatic effects, like leukemia, are plotted on a
linear dose-response curve.
The nonlinear/sigmoidal dose-response curve has a threshold and is thought to be generally correct for most
somatic effects
Which of the following accounts for the x-ray beam's heterogeneity?
1. Incident electrons interacting with several layers of tungsten target atoms
2. Energy differences among incident electrons
3. Electrons moving to fill different shell vacancies
During characteristic x-ray production, vacancies may be filled in
the K, L, or M shells, which differ from each other in binding energies, and therefore photons with varying amounts of energy are emitted
in vivo
within a living system
Photoelectric
complete absorption of the incident photon
Compton
partial transfer of energy.
Which of the following has/have been identified as sources of radon exposure?
1. indoors, in houses
2. smoking cigarettes
Irradiation of macromolecules in vitro can result in
1. main chain scission.
2. cross-linking.
3. point lesions.
Irradiation damage is a result of either the effects of
irradiation on water (radiolysis) or its effects on macromolecules
Main chain scission
breaks the DNA molecule into two or more pieces.
Cross-linking
incorrect joining of broken DNA fragments.
point lesion
the disruption of a single chemical bond as a result of irradiation.
Because 80% of the body is made up of water,
radiolysis of water is the predominant radiation interaction in the body
What is the term used to describe x-ray photon interaction with matter and the transference of part of the photon's energy to matter?
Scattering
Scattering
occurs when there is partial transfer of the proton's energy to matter, as in the Compton effect.
Absorption
occurs when an x-ray photon interacts with matter and disappears, as in the photoelectric effect
The reduction in the intensity (quantity) of an x-ray beam, as it passes through matter, is termed
attenuation.
Divergence
refers to a directional characteristic of the x-ray beam, as it is emitted from the focal spot
Late effects of radiation, whose incidence is dose related and for which there is no threshold dose, are referred to as
stochastic
How do fractionation and protraction affect radiation dose-effects?
1. They reduce the effect of radiation exposure.
2. They permit cellular repair.
3. They allow tissue recovery.
Stochastic effects of radiation are those that
1. may be described as "all-or-nothing" effects.
2. are late effects.
Which of the following are considered especially radiosensitive tissues?
1. Blood-forming organs
2. Reproductive organs
3. Lymphocytes
Excessive radiation to the reproductive organs can cause
genetic mutations or sterility.
Excessive radiation to the blood-forming organs can cause
leukemia or life span shortening.
Lymphocyte cells
the most radiosensitive cells in the body.
Which of the following statements regarding the human gonadal cells is (are) true?
1. The female oogonia reproduce only during fetal life.
2. The male spermatogonia reproduce continuously.
photoelectric effect
an inner-shell electron
In radiation protection, the product of absorbed dose and the correct modifying factor (rad x QF) is used to determine
rem (Sv)
Rem
(dose-equivalent) is the only unit of measurement that expresses the dose-effect relationship.
The product of rad (absorbed dose) and the quality factor appropriate for the radiation type is expressed as
rem or DE (dose equivalent), and may be used to predict the type and extent of response to radiation.
Alpha and beta radiation are
particulate radiations; alpha is composed of two protons and two neutrons, and beta is identical to an electron.
Gamma and x-radiation are
electromagnetic, having wavelike fluctuations like other radiations of the electromagnetic spectrum (visible light, radio waves, etc).