reading: chapter 4. radiation biology is the study of the effects of radiation on living tissue. ...
TRANSCRIPT
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Radiation Biology Reading: Chapter 4
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Radiation Biology is the study of the effects of radiation on living tissue.
X-rays are a form of ionizing radiation. When x-rays strike patient tissues, ionization results.
All ionizing radiations are capable of producing biologic changes in living tissue.
Radiation Biology
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Effects of Ionization
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ATOMSwhich may affect
MOLECULESwhich may affect
CELLSwhich may affect TISSUES
which may affect ORGANS
which may affect THE WHOLE BODY
Radiation Causes Ionization of:
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Direct Theory◦when radiation interacts with atoms of the DNA molecule, it may affect the ability of a cell to reproduce and survive.
◦Direct injuries from exposure to ionizing radiation occur infrequently.
Theories of Radiation Injury:
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Indirect Theory: when x-ray photons are absorbed within the water
inside a cell it can cause the formation of toxic substances. (water to hydrogen peroxide!)
This can ultimately lead to the destruction of the cell.
Injuries of this type occur frequently because our body cells contain so much water. (70 – 80% water!)
Theories of Radiation Injury
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Free Radical Formation
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So…if ALL ionizing radiation is harmful, what level of exposure is considered “acceptable”?
With radiation exposure, a dose-response curve can be used to correlate the:◦Response (or damage) to the tissue ◦With the:◦Dose (or amount) of the radiation received
Dose Response Curve
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Turn to page 36 in your books. With radiation a “linear non-threshold”
relationship is seen. A LINEAR relationship indicates that the
response of the tissues is DIRECTLY PROPORTIONAL to the dose level.
A non-threshold relationship indicates that a threshold lose level DOES NOT EXIST for radiation.
Dose Response Curve
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Threshhold Curve
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The Latent Period The Period of Injury The Recovery Period
Sequence of Radiation Injury
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The latent period is defined as the time between exposure to x-rays, and the appearance of radiation damage.
This is the first step in the sequence of radiation injury.
The Latent Period
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The latent period can be short or long depending upon:◦ Total dose of radiation received◦ The amount of time, or rate, it took to receive the
dose. As you may expect:
◦ The MORE radiation received and ◦ The FASTER the dose rate, ◦ The SHORTER the latent period
The Latent Period
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A variety of cell injuries may occur.◦ Cell death◦ Changes in cell function◦ Breaking or clumping of chromosomes◦ Formation of giant cells◦ Abnormal cell division or cessation of cell division
The Period Of Injury
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Not all cellular radiation injuries are permanent!
Most damage caused by low-level radiation injury is repaired within the body’s cells!!
Scatter Radiation remains in cells, but the body can slough it off in 24-48 hours. However, repeated exposure does not allow the body time to adjust.
The Recovery Period
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The effects of radiation exposure are additive, and unrepaired damage accumulates in the tissues.
The cumulative effects of repeated exposure can lead to health problems.◦ Cancer◦ Cataract formation◦ Birth defects
◦ See table 4-1 at the bottom of page 37.
There is a CUMULATIVE EFFECT
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Total Dose:◦ Greater damage with larger amounts of radiation
Dose Rate:◦ A high dose rate does not allow time for cellular
damage to be repaired. Amount of tissue radiated:
◦ Total body irradiation produces more adverse effects than if small, localized areas of the body are exposed.
Cell sensitivity Age
Factors Affecting Radiation Injury
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Cell sensitivity:◦ More damage occurs in cells that are rapidly
dividing. Age:
◦ Children are more susceptible to radiation damage than adults.
Factors Affecting Radiation Injury
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Short Term Effects: high doses of radiation over short periods of time tend to kill cells.◦ Death◦ Skin burns (erythemia), peeling, blistering◦ Hair loss◦ Sterility◦ Cataracts
Long Term Effects: low doses of radiation over extended period of time produce chronic, or long-term effects, which may not be observed for many years.
Short Term and Long Term Effects:
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Somatic Effects: Occur in all cells of the body except the
reproductive cells. These changes are not passed along to
future generations. They only affect the individual exposed. Primary consequence is cancer
Somatic and Genetic Effects:
www.ehow.com/video_49847#25537E
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Genetic Effects: Occur in reproductive cells Are passed along to future generations These changes do not affect the exposed
individual, but are passed along by mutations in offspring.
Genetic damage cannot be repaired
Somatic and Genetic Effects
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Somatic VS Genetic Effects of Radiation
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Tissues and organs vary with their sensitivity to radiation.
Radiosensitive organs include:◦ Lymphoid tissue (small lymphocyte)◦ Bone marrow (blood forming tissue)◦ Testes◦ Intestines
Radioresistant organs include:◦ Salivary glands◦ Kidney ◦ liver
Tissue & Organ Sensitivity
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A critical organ is an organ that, if damaged, would diminish the quality of a person’s life.
In dentistry, some tissues and organs are designated as critical because they are exposed to more radiation than others during dental radiographic procedures.
Critical Organs
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The critical organs exposed during dental radiographic procedures include:◦Skin◦Thyroid gland◦Lens of the eye◦Bone marrow (aka: blood forming tissue)
◦Turn to page 41 of your text
Critical Organs
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Critical Organs
Panoramic X-ray Exposure Bite-wing X-ray Exposure
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Currently 2 systems are used Traditional/Standard System
◦ Roentgen (R)◦ Radiation absorbed Dose (rad)◦ Roentgen equivalent (in) man (rem)
SI System◦ Coulombs/kilogram (C/kg)◦ Gray (Gy)◦ Sievert (Sv)
Radiation Measurement
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Roentgen (R)- ◦ This is the traditional unit of exposure. ◦ That is the amount of ionization created in a given
volume of air.
Exposure Measurement - R
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Radiation absorbed dose (rad) This is the traditional unit of dose Dose can be defined as the amount of
energy absorbed by a tissue.
Dose Measurement - RAD
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Different types of radiation have different effects on tissue.
The dose equivalent measurement is used to compare the biological effects of different types of radiation
In the traditional system, the unit of dose equivalent is roentgen equivalent (in) man or rem.
Dose Equivalent Measure - REM
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Radiation can come from 2 sources:
◦ Natural Background Radiation: this radiation comes from the sun, earth, and atmosphere
◦ Artificial Radiation: (man-made) medical/dental x-rays, nuclear, consumer products
Sources of Radiation
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Sources of Radiation
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Sources of Radiation
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Sources of Radiation
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Smoke detectors that use “americium”-241 Lawn fertilizer containing potassium-40Cigarettes Gas lanterns Exit signs Natural gas appliancesBrick or stone housesColor television sets
Consumer Products
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Fukashima Nuclear Disaster
www.youtube.com/watch?v=#2553F2
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Radiation is harmful to living tissue. Because biological damage results from x-
ray exposure, dental radiographs should be prescribed ONLY WHEN the benefit of disease detection outweighs the risk of biologic damage.
When dental x-rays are properly prescribed and exposed, the benefit far outweighs the risk.
Risk vs. Benefit Principle
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Pro and Cons of Dental Radiation Pros Can help to detect:
◦ Caries◦ Cysts◦ Tooth abscess/infection◦ Retained Roots/Foreign
Bodies◦ Periodontal Disease◦ Foreign Bodies◦ Growth Irregularities◦ Tooth Development◦ Tooth impactions
Cons Tissues that can be
effected by radiation:◦ Embryonic tissue◦ Blood and bone marrow◦ Skin◦ Connective tissue◦ Nerve◦ Brain◦ Muscle cells◦ Enamel
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The ADA sets guidelines for how frequently patients should have radiographs taken based on many factors.
We will discuss these in the next section of this course on “Radiation Protection”.
Guidelines for Radiation Exposure for Dental Patients