Quiz 3 Chapter 4 Flashcards
Radiation Biology
All ionizing radiations are ___ and produce ____ changes in living tissues
harmful
biologic
Radiation Biology
The study of the effects of ionizing radiation on living tissue
Absorption
Refers to the total transfer of energy from the xray photon to patient tissues
Two specific mechanisms of radiation injury are possible
1) Ionization
2) Free radical formation
X-rays are a form of ionizing radiation; when
xrays strike patient tissues
ionization is produced through the photoelectric effect or Compton scatter and results in the
formation of a positive atom and a dislodged negative electron.
The ejected high-speed electron is set into motion and interacts with other atoms within the absorbing tissues. The kinetic energy of such electrons results in further ionization, excitation, or breaking of molecular bonds, all of which cause chemical changes within the cell that result in biologic damage
X-radiation causes cell damage primarily through the formation of __ ___
free radicals
Free radical formation occurs when an x-ray photon ionizes ___ the primary component of living cells. Ionization of water results in the production of ___ and ____ ____ ____
water
hydrogen
hydroxyl free radicals
A free radical is an _____ atom or molecule that exists with a single, unpaired electron in its outermost shell. It is highly reactive and unstable; the lifetime of a free radical is approximately ___ seconds.
uncharged neutral
10^ 10
To achieve stability, free radicals may :
1.
2.
3.
(1) recombine without causing changes in the molecule, (2) combine with other free radicals and cause changes, or (3) combine with ordinary molecules to form a toxin (e.g., hydrogen peroxide [H 2 O 2 ]) capable of producing widespread cellular changes
2 Theories used to describe how radiation damages biologic tissues
- The direct theory
2. The indirect theory
indirect theory of radiation injury suggests that:
x-ray photons are absorbed within the cell and cause the formation of toxins, which in turn damage the cell
An indirect injury results
because the free radicals combine and form toxins, not because of a direct hit by x-ray photons.
Indirect injuries from exposure to ionizing radiation occur
frequently or not
and why
frequently because the high water (70-80%) content of cells.
To establish acceptable levels of radiation exposure, it is useful to plot the __ ___and the ___ ____
dose administered
damage produced
With radiation exposure, a ___ ___ ___ can be used to correlate the “response,” or damage, of tissues with the “dose,” or amount, of radiation received.
dose response curve
When dose and damage are plotted on a graph, a __, ____ relationship is seen
linear
nonthreshold
A linear relationship indicates that :
the response of the tissues is directly proportional to the dose.
A ____relationship indicates that a threshold dose level for damage does not exist.
nonthreshold
A nonthreshold dose-response curve suggests that no matter how small the amount of radiation received, some __ ____does occur
biologic damage
The deleterious effects of ionizing radiation on human tissue can be divided into two types: ___and ___
stochastic
nonstochastic
Stochastic Effects
occur as a direct function of dose
Stochastic Effects: The probability of occurrence increases with ___ ___ ____; however, the severity of effects does not depend on the magnitude of the absorbed dose. As in the case of nonthreshold radiation effects, stochastic effects do not have a dose threshold.
increasing absorbed dose
Stochastic effects occur due to the effect of ionizing radiation on chromosomes that result in ___ ____Examples of stochastic effects include induction of leukemia and other cancers (i.e., tumors).
genetic mutations
Nonstochastic effects only occur after a threshold of exposure has been ____
exeeded
have a threshold and increase in severity with increased absorbed dose.
Nonstochastic effects
The severity of deterministic effects/nonstochastic effects increases as the dose of exposure ___
increases
Because of an identifiable ___ ____, appropriate radiation protection mechanisms and occupational exposure dose limits can be put in place to reduce the likelihood of these effects occurring.
threshold level
Nonstochastic effects are caused by ____ __ ___ (lethal DNA damage) or cell death. The physical effects occur when the cell death burden is large enough to cause obvious ___ ____ of a tissue or organ.
significant cell damage
functional impairment
Examples of nonstochastic effects
skin erythema Loss of hair cataract formation decreased fertility radiation sickness teratogenesis fetal death
Which radiation effect requires larger radiation doses to cause serious impairment or death
nonstochastic
Chemical reactions (e.g., ionization, free radical formation) that follow the absorption of radiation occur rapidly at the molecular level. However, varying amounts of ___ are required for these changes to alter cells and cellular functions.
As a result the observable effects of radiation are not visible immediatlely after exposure, instead, following exposure a
- time
- latent period occurs
Latent Period
time that elapses between exposure to ionizing radiation and the appearance of observable clinical signs
latent period may be short or long, depending on the total dose of radiation received and the amount of time, or rate, it took to receive the dose. The more radiation received and the faster the dose rate, the ___ the latent period.
shorter
After the latent period, a period of
injury occurs
-variety of cellular injuries may result including cell death, changes in cell function, breaking or clumping of chromosomes, formation of giant cells, cessation of mitotic activity, abnormal mitotic activity
The last event in the sequence of radiation is the ___
recovery period
Not all cellular injuries are permanent. With each radiation exposure, cellular damge is followed by
repair
The effects of radiation exposure are additive and unreparied damage accumulates in the
tissues
The Factors used to determine the degree of radiation injury include the following
Total Dose Dose Rate Amount of Tissue Irradiated Cell Sensitivity Age
Quantity of radiation received, or the total amount of radiation energy absorbed. More damage occurs when tissues absorb large quantities of radiation.
Total Dose
