ch05_lecture

Report
Essentials of Dental Radiography
for Dental Assistants and Hygienists
NINTH EDITION
CHAPTER
5
Effects of Radiation
Exposure
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Objectives
• Define the key words.
• Explain the difference between the direct
and indirect theories of biological damage.
• Determine the relative radiosensitivity or
radioresistance of various kinds of cells in
the body.
• Explain the difference between somatic
and genetic effects.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Objectives
• Explain the difference between a threshold
dose–response curve and a non-threshold
dose–response curve.
• Identify the factors that determine radiation
injuries.
• List the sequence of events that may
follow exposure to radiation.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Objectives
• Explain the difference between
deterministic and stochastic effects.
• List the possible short- and long-term
effects of irradiation.
• Identify critical tissues for dental
radiography in the head and neck region
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Objectives
• Discuss the risks versus benefits of dental
radiographs.
• Utilize effective dose equivalent to make
radiation exposure comparisons.
• Adopt an ethical responsibility to follow
ALARA.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Key Words
•
•
•
•
•
•
Acute radiation syndrome (ARS)
ALARA (as low as reasonably achievable)
Cumulative effect
Deterministic effect
Direct theory
Dose–response curve
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Key Words
•
•
•
•
•
•
•
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Genetic cells
Genetic effect
Genetic mutations
Indirect theory
Ionization
Irradiation
Irreparable injury
Latent period
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Key Words
•
•
•
•
•
•
Law of B and T
Lethal dose (LD)
Non-threshold dose–response curve
Period of injury
Radiolysis of water
Radioresistant
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Key Words
•
•
•
•
•
•
•
Radiosensitive
Recovery period
Risk
Somatic cells
Somatic effect
Stochastic effect
Threshold dose–response curve
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Introduction
• Patients are often concerned with the
safety of dental x-ray procedures.
• Oral health care professionals share the
same concerns.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Introduction
• Because even the experts cannot always
predict a specific outcome from an amount
of radiation exposure, the radiation
protection community conservatively
assumes that any amount of radiation may
pose a risk.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Theories of Biological Effect
Mechanisms
• Ionization
• Direct theory
• Indirect theory (radiolysis of water)
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Figure 5-1 Direct theory and indirect theory. In the direct theory, x-ray photons collide with large molecules and
break them apart by ionization. The indirect theory is based on the assumption that radiation can cause chemical
damage to the cell by ionizing the water within it.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Figure 5-2 Indirect theory. X-rays ionize water, resulting in the formation of free radicals, which recombine to form
toxins.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Cell Sensitivity
to Radiation Exposure
•
•
•
•
•
•
Radiosensitive
Radioresistant
Law of B and T
Somatic effect
Genetic effect
Cumulative effect
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Cell Sensitivity
to Radiation Exposure
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•
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•
•
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•
•
•
White blood cells (lymphocytes)
Red blood cells (erythrocytes)
Immature reproductive cells
Epithelial cells
Endothelial cells
Connective tissue cells
Bone cells
Nerve cells
Brain cells
Muscle cells
High sensitivity
Low sensitivity
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
The Dose-Response Curve
• Response curve
• Threshold dose-response curve
• Non-threshold dose-response curve
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Figure 5-3 Diagram of dose–response curve. (A) A typical “threshold” curve. The point at which the curve intersects
the base line (horizontal line) is the threshold dose that is the dose below which there is no response. If an easily
observable radiation effect, such as erythema (reddening of the skin) is taken as “response,” then this type of curve is
applicable. (B) A linear “non-threshold” curve, in which the curve intersects the base line at its origin. Here it is assumed
that any dose, no matter how small, causes some response.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
The Dose-Response Curve
ALARA
“As Low As Reasonably Achievable”
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Factors that Determine Radiation
Injury
• Five outcomes:
– Nothing, the cell is unaffected by the
exposure
– Cell is injured or damaged but repairs itself
and functions at pre-exposure levels
– Cell dies, but is replaced through normal
biological processes
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Factors that Determine Radiation
Injury
• Five outcomes:
– Cell is injured or damaged, repairs itself, but
now functions at a reduced level
– Cell is injured or damaged, and repairs itself
incorrectly or abnormally, resulting in a
biophysical change (tumor or malignancy)
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Factors that Determine Radiation
Injury
• Outcomes depend on:
– Total dose
– Dose rate
– Area exposed
– Variation in species
– Individual sensitivity
– Variation in cell sensitivity
– Variation in tissue sensitivity
– Age
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Sequence of Events Following
Radiation Exposure
• Latent period
• Period of injury
• Recovery period
Assumption: dose received was non-lethal
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Figure 5-4 Concept of accumulated irreparable injury. After exposure to radiation cell recovery can take place.
However, there may be a certain amount of damage from which no recovery occurs, and it is this irreparable injury that
can give rise to later long-term effects.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Radiation Effects
on Tissues of the Body
• Deterministic (non-stochastic) Effect —
when the severity of the change is
dependent on the dose
• Stochastic Effect — when a biological
response is based on the probability of
occurrence rather then the severity of the
change (i.e., cancer)
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Short- and Long-term Effects of
Radiation
• Short-term effects of radiation are those
seen minutes, days, or months after
exposure.
• Acute Radiation Syndrome (ARS)
symptoms include erythema, nausea,
vomiting, diarrhea, hemorrhage, and hair
loss.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Short- and Long-term Effects of
Radiation
• Long-term effects of radiation are those
that are seen years after the original
exposure.
• The long-term effects observed are
somatic damage, which may result in an
increased incidence of cancer,
embryological defects, low birth weight,
cataracts, and genetic mutations.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Figure 5-5 Ulcerated lesion. Early carcinoma on the finger of a dentist who admitted holding films in the patient’s oral
cavity during exposure.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Figure 5-6 Radiation injury on the finger of a dentist caused by holding films in the patient’s oral cavity
during exposure. A lesion of this type would be likely to result in squamous cell carcinoma (cancer).
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Risk Estimates
• A risk may be defined as the likelihood of
injury or death from some hazard.
• The primary risk from dental radiography
is radiation-induced cancer and, possibly,
the potential to affect pregnancy
outcomes.
• Risk estimates vary, depending on several
factors, such as speed of film, collimation,
and the technique used.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Risk Estimates
• In dental radiography, the most critical
tissues of the head and neck are the
mandible (red bone marrow), the lens of
the eye, the thyroid gland, and possibly
the hypothalamus-pituitary-thyroid
combination.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Table 5-1 Critical Organs and Doses for Dental
Radiograpy
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Table 5-2 One in One Million Fatality Risk
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Table 5-3 Effective Dose Equivalent
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Review: Chapter Summary
• Ionizing radiation has the potential to
produce biological damage.
• There are two generally accepted theories
on how radiation may cause damage to
cellular tissues: direct theory and
indirect theory.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Review: Chapter Summary
• The terms radiosensitive and
radioresistant are used to describe the
degree of susceptibility of various cells
and body tissues to radiation.
• Biological changes or damage that occur
in somatic cells will affect the irradiated
individual but will not passed down.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Review: Chapter Summary
• Biological changes or damage that do not
affect the irradiated individual but are
passed to future generations are called
genetic effects.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Review: Chapter Summary
• The dose–response curve is a method
used to plot the dosage of radiation
administered with the response produced
to establish responsible levels of radiation
exposure.
• ALARA — as low as reasonably
achievable. Every dose of radiation should
be kept to a minimum.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Review: Chapter Summary
• Factors that influence a biological
response to irradiation: dose amount, dose
rate, area exposed, species exposed,
individual sensitivity, cell sensitivity, tissue
sensitivity, and age.
• Sequence of events following radiation:
latent period, a period of injury, and
recovery period.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Review: Chapter Summary
• Deterministic-tissue response that is
directly related to the radiation amount.
Stochastic effect is tissue response that is
based on the probability of occurrence
rather than severity.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Review: Chapter Summary
• Short- or long-term effects:
– Short — erythema and general discomfort
– Long — an increased incidence of cancer,
embryological defects, poor pregnancy
outcomes, cataracts, and genetic mutations.
• The potential benefits of dental
radiographs outweigh the risk.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Recall: Study Questions
• General
• Chapter Review
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Reflect: Case Study
• Retaking a radiograph because of a
technique or processing error causes an
increase in radiation exposure for the
patient. Discuss ways a retake radiograph
affects the factors that determine radiation
injury.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.
Relate: Laboratory Application
• Proceed to Chapter 5, Laboratory
Application, to complete this activity.
Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth Edition
Evelyn M. Thomson • Orlen N. Johnson
Copyright ©2012 by Pearson Education, Inc.
All rights reserved.

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