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
Rate at which exposure to radiation occurs and absorption takes place (dose rate = dose/time). More radiation damage takes place with high dose rates because a rapid delivery of radiation does not allow time for the cellular damage to be repaired.
Dose Rate
Areas of the body exposed to radiation. Total-body irradiation produces more adverse systemic effects than if small, localized areas of the body are exposed. An example of total-body irradiation is the exposure of a person to a nuclear energy disaster. Extensive radiation injury occurs when large areas of the body are exposed because of the damage to the blood-forming tissues.
Amount of tissue irradiated
Cell Sensitivity
More damage occurs in cells that are most sensitive to radiation, such as rapidly dividing cells and young cells
Age
Children are more susceptible to radiation damage than are adults
Following the latent period, effects that are seen within minutes, days or weeks are termed
short term effects
Associated with large amounts of radiation absorbed in a short time (exposure to nuclear accident, atomic bomb)
Short Term Effects
Radiation
short-term effect and includes nausea, vomiting, diarrhea, hair loss, and hemorrhage. Short-term effects are not applicable to dentistry.
Acute Radiation Syndrome
Effects that appear after years, decades, or generations are termed
long-term effects
associated with small amounts of radiation absorbed repeatedly over a long period.
Long term effects
Repeated low levels of radiaiton exposrue are linked to the induction of
cancer, birth abnormalities, genetic defects
All the cells in the body can be classified as either somatic or __
Define what both are:
genetic
Somatic cells are all the cells in the body except the reproductive cells. The reproductive cells (e.g., ova, sperm) are termed genetic cells .
Somatic effects are seen in a person who has been irradiated. Radiation injuries that produce changes in somatic cells produce __ ___in the irradiated individual.
poor health
Major somatic effects of radiation exposure include the induction of cataracts and cancer, including leukemia. These changes, however, are not transmitted to ___ ____
future generations
Genetic effects are not seen in the irradiated person but are passed on to ___ ____ Radiation injuries that produce changes in genetic cells
(do or do not)
affect the health of the exposed individual. Instead, the radiation-induced mutations affect the health of the offspring (see Figure 4-5 ). Genetic damage cannot be repaired.
future generations
do affect the health
Ionizing radiation may affect the nucleus, cytoplasm or the entire cell
The cell ___ is more sensitive to radiation than is the cytoplasm
nucleus
A cell that is sensitive to radiation is termed
radiosenstive
One that is resistant is termed
radioresistant
The response of a cell to radiation exposure is determined by the following
-Mitotic Activity: Cells that divide frequently or undergo many divisions over time are moe sesntive to radiation
-Cell Differentiation
Cells that are immature or are not highly specialized are more sensitive to radiation.
-Cell Metabolism
Cells that have a higher metabolism are more sensitive to radiation. Cells that are radiosensitive include blood cells, immature reproductive cells, and young bone cells.
Cels that are radiosensitve include
blood cells
immature reproductive cells
young bone cells
The cell most sensitive to radiation is the small lymphocyte. Radioresisitant cells include
bone
muscle
nerve
Radiosensitive organs are composed of radiosensitive cells and include :
Examples of radioresistant tissues include: the salivary glands, kidney, and liver.
lymphoid tissues, bone marrow, testes, and intestines.
CRITICAL ORGAN IS AN ORGAN THAT
examples
if damaged diminishes the quality of a persons life.
- Thyroid gland
- Bone marrow
- Skin
- Lens of eye
Radiation can be measured in the same manner as other physcial conecpts such as
time, distance, weight
International Comission on Radiation Unit and Measurements has established special units for measurment of radiaiton. 3 QUANTITIES OF RADIAITON
- EXPOSURE
- DOSE
- DOSE EQUIVALENT
• Roentgen (R) • Radiation absorbed dose (rad) • Roentgen equivalent (in) man (rem)
TRADITIONAL UNITS
Gray (Gy) • Sievert (Sv)
SI UNITS OF RADIATION
exposure
refers to the measurement of ionization in air produced by x-rays.
The roentgen has limitations as a unit of measure. It measures the amount of energy that reaches the surface of an organism but does not describe the amount of radiation absorbed. The roentgen is essentially limited to ____ _ _____. By definition, it is used only for x-rays and gamma rays and does not include other types of radiation.
measurements in air
Dose
can be defined as the amount of energy absorbed by a tissue
Radiation absorbed dose or rad
traditional unit of dose/can be applied to all forms of radiaiton
Measurement that is used to compare the biologic effects of different types of radiation
dose equivalent
The traditional unit of dose equivalent is the
roentgen equivalent man or rem
In measuring the roentgen, a known volume of ___ is irradiated. The interaction of x-ray photons with air molecules results in ionization, or the formation of ions. The ions (electrical charges) that are produced are ____ and ____.
air
collected
measured
1 roentgen =
2 billion ion pairs in one cubic centimeter of air
Roentgen measures the amount of energy that reaches the surface of an organism but does not describe the amount of radiation ____
absorbed
used only for xrays and gamma rays and does not include other types of radiaiton
Roentgen
Coulomb
unit of electrical charge. The unit C/kg measures the number of electrical charges, or the number of ion pairs, in 1 kg of air.
Dose
Defined as the amount of energy absorbed by a tissue
Radiation absorbed dose or rad is the ____ unit of dose
Non traditional or Traditional
Traditional
Different types of radiation have different effects on
tissues
measurement is used to compare the biologic effects of different types of radiaiton
Dose Equivalent
The traditional unit of dose equivalent is the
roentgen equivalent (in) man, or rem
To place the exposure effects of different types of radiation on a common scale, a __ ___ , or dimensionless multiplier, is used.
Quality Factor
Each type of radiation has a specific ___ ____ based on different types of radiation producing different types of biologic damage. For example, the QF for x-rays is equal to 1.
QF or Qualtiy Factor
In dental imaging, the gray and __ are equal, and the roentgen, __ and __ are considered approximately equal.
Sievert
rad and rem
Natural or Background Radiation sources include
Radon in the air
Uranium
Radium
Thorium in the earth
Cosmic rays
Radioactive potassium in food and water
Radioactive material found within human
body
The single greatest source of expsoure to background radiation in the united states
Radon gas
is the greatest contributer to human made radiaiton exposure
Medical Radiaiton
___ to background radiation varies depdning on where a person lives
exposure
depends on the elevation above sea level; the higher the altitude, the more exposure to cosmic rays.
Cosmic exposure
comes from the ground; an example includes naturally occurring uranium-enriched soil.
terrestrial Exposure
___ radiation depends on the food and water that person ingests
- bananas and brazil nuts example
- water supply
Internal radiaiton
In the United States, the average person is exposed to a total of __ mSv of radiation per year (__ mSv from natural sources + __mSv from human-made sources = __mSv total).
6.2 mSv
- 1 mSv from natural sources
- 1 mSv from human made
luminous wristwatches televisions computer screens fallout atomic weapons nuclear fuel cycle
human made radiation exposure
__ radiation is the greatest contributer to human made radiation exposure
medical
medical imaging procedures dental imaging radiation therapy nuclear medicine computed tomography
medical radiation
Dental Imaging Critical Organs or Risk Elements
Thyroid Gland
Bone Marrow
Skin
Eyes
To calculate the risk from dental imaging procedures, ___ to crtitical organs must be measured
doses
The amount of exposure varies depending on the follwoing
Receptor choice-digital F
Collimation
Technique
The amount of exposure varies depending on the follwoing
Receptor choice-digital F
Collimation: Rectangular
Technique: Radiation exposure can be limited by increasing the target receptor distance /paralleling
