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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5196_Библиотеки_им_академика_М_И_Перельмана.pdf
ACKNOWLEDGMENTS
xix
this textbook, it is my hope that the material contained
within this edition will greatly contribute to providing
you with a foundation in radiation protection/safety
and radiation biology and the means to enhance your
knowledge in this subject matter. Education is an ongoing process; each person who enters into radiation
sciences profession assumes a responsibility to continue
learning to enhance their skills and overall knowledge.
This growth will enable imaging professionals including
American registered radiologic technologists, radiologists, medical physicists, and referring physicians to
better serve patients entrusted to their care.
Finally, as I have stated in previous editions of this
text, a very special remembrance is given to my parents,
the late Felix and Elizabeth (Markovitch) Krohn, for
all they did for me. Their many words of wisdom and
lifelong encouragement remain with me. The education
in my chosen profession they made possible helped
me gain the knowledge and motivation necessary to
prepare this new and previous editions. My personal
accomplishments in the field of medical imaging serve
as a tribute to them.
Mary Alice Statkiewicz Sherer, AS, RT(R), FASRT
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C O N T E N T S
1 Introduction to Radiation Protection, 1
2 Radiation: Types, Sources, and Doses
Received, 16
3 Interaction of X-Radiation With Matter, 34
4 Radiation Quantities and Units, 54
5 Radiation Monitoring, 72
6 Overview of Cell Biology, 88
7 Molecular and Cellular Radiation Biology, 111
8 Early Tissue Reactions and Their
Effects on Organ Systems, 137
9 Stochastic Effects and Late Tissue
Reactions of Radiation in Organ Systems, 153
10 Dose Limits for Exposure to Ionizing
Radiation, 173
11 Equipment Design for Radiation Protection, 194
12 Management of Patient Radiation Dose During
X-Ray Procedures, 227
13 Special Considerations on Safety in Computed
Tomography, 252
Appendix A: Relationships Between Systems
of Units, 343
Appendix B: Image Gently Pledge and Image Wisely
Pledge, 345
Appendix C: Standard Designations for Metric
System Lengths, Electron Volt Energy
Levels, and Frequency Spectrum
Ranges, 347
Appendix D: Periodic Table of Elements, 349
Appendix E: Relationship Among Photons,
Electromagnetic Waves, Wavelength,
and Energy, 351
Appendix F: Electron Shell Structure of the Atom, 352
Appendix G: Compton Interaction, 354
Appendix H: NCRP 10CFR Part 35.50 Training for
Radiation Safety Officer and Associate
Radiation Safety Officer, 356
Appendix I: Consumer-Patient Radiation Health
and Safety Act of 1981, 358
References, 362
Glossary, 370
Index, 392
14 X-Ray Breast Imaging: Methods and Radiation
Safety Aspects, 275
15 Management of Imaging Personnel Radiation
Dose During Diagnostic X-Ray Procedures, 293
16 Radioisotopes and Radiation Protection, 319
xxi
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Introduction to Radiation Protection
O B J E C T I V E S
After completing this chapter, the reader will be able to
perform the following:
• Define all key terms.
• Identify the consequences of ionization in human
cells.
• List the properties, or characteristics, of x-rays.
• Describe the concept of teamwork in the medical
field, and state the potential benefit that such an
organized collaborative approach can have on
radiation safety.
• Give examples of how radiologic technologists and
radiologists can exercise control of radiant energy
while performing imaging procedures.
• State the goals and discuss the concept of radiation
protection.
• List the three main types of radiation quantities
and identify the unit(s) of measure in which each
quantity is specified.
• Explain the justification and responsibility for
imaging procedures.
• Explain how diagnostic efficacy of an imaging
procedure can be maximized.
1
• State the As Low As Reasonably Achievable
(ALARA) principle and discuss its significance in
diagnostic imaging.
• List the three basic principles of radiation protection.
• List employer requirements for implementing and
maintaining an effective radiation safety program
in a facility that provides imaging services and
identify the responsibilities that radiation workers
must fulfill.
• Describe the importance of patient education as it
relates to medical imaging.
• Explain how radiographers should answer patients’
questions about the risk of radiation exposure from
an imaging procedure and give some examples.
• Compare radiation sensitivity of children with
radiosensitivity of adults.
• Explain the difference between the Image Gently
Campaign and the Image Wisely Campaign.
• Discuss the Pause and Pulse: Image Gently in
Fluoroscopy Campaign.
• Discuss the reasons for monitoring and reporting
radiation dose.
C H A P T E R O U T L I N E
Team Concept in the Medical Field
Control of Radiant Energy
Goals of Radiation Protection
Concept of Radiation Protection
Introduction to Radiation Quantities and Units of
Measure
Need to Safeguard Against Adverse Biologic Effects
of Ionizing Radiation
Justification and Responsibility for Imaging
Procedures: Benefit Verses Risk
Diagnostic Efficacy
As Low As Reasonably Achievable (ALARA) Principle
Cardinal Rules for Radiation Protection
Responsibility for Maintaining ALARA in the
Medical Industry
Patient Protection and Patient Education
Educating Patients About Imaging Procedures
Risk of Imaging Procedures Verses Potential Benefit
Background Equivalent Radiation Time
Increased Radiation Sensitivity of Children
Alliance for Radiation Safety in Pediatric Imaging
Image Gently Campaign
1
2
CHAPTER 1 Introduction to Radiation Protection
Image Wisely Campaign
Monitoring and Reporting Radiation Dose
The NEXT Program and Reference Values
K E Y T E R M S
absorbed dose
ALARA
alert levels
Alliance for Radiation Safety in
Pediatric Imaging
background equivalent radiation
time
biologic effects
coulomb per kilogram (C/kg)
diagnostic efficacy
The transfer of energy from one location to another is
called radiation. It has been present on this planet in
all of its various manifestations since the beginning of
time. The use of radiation within the healing arts did
not occur until after the discovery of an energetic form
of radiation called x-rays in 1895. Since the early
1900s, both their beneficial and destructive potentials
have been known. When passing through normal matter, x-rays were observed to produce electrically
charged particles along their path. The altered atoms
or molecules comprising these charged particles were
called ions. Because of this effect the x-rays were classified as ionizing radiation. The production of these
ions, as well as the electrons ejected in the process, is
the event that may cause injury in normal biologic tissue. Consequences of ionization in human cells are
listed in Box 1.1.
In the years following their discovery, most of the
fundamental properties of x-rays were discovered by
experiment. Briefly, they can be described as follows:
• X-rays are invisible.
• X-rays can have varying degrees of penetration in
normal tissue, ranging from very superficial (skin
surface) to much deeper (5 cm or greater) depending
on their energy.
• X-rays are not deflected from their paths by either
electric or magnetic fields and so are classified as
electrically neutral.
• Although visible light may be focused with a lens,
x-rays cannot.
effective dose
exposure
gray (Gy)
Image Gently Campaign
Image Wisely Campaign
ionizing radiation
milligray (mGy)
milliroentgens (mR)
millisievert (mSv)
Protocols for Dose Alerts
Summary
optimization for radiation
protection (ORP)
Pause and Pulse: Image Gently in
Fluoroscopy Campaign
radiation
radiation protection
reference values
risk
Sievert (Sv)
BOX 1.1 Consequences of Ionization in
Human Cells*
• Creation of unstable atoms
• Production of free electrons
• Production of low-energy x-ray photons
• Creation of highly reactive free molecules (called free
radicals) capable of producing substances poisonous
to the cell
• Creation of new biologic molecules detrimental to
the living cell
• Injury to the cell that may manifest itself as abnormal
function or loss of function
*Each of these consequences is fully discussed in subsequent
chapters.
• X-rays travel in straight lines and at the speed of light
(300 million meters per second) until they interact
with atoms.
• When passing through matter, x-rays will produce
charged particles by interaction with atoms composing that matter, as well as cause an emission of light
known as fluorescence in certain crystals.
• X-rays will darken photographic film, with the degree
of darkening on portions of the film being associated
with the intensity (amount or quantity) of the x-rays
striking those portions.
• X-ray beams generally have within them a wide
range of energies; that is, x-ray beams are normally
heterogeneous instead of monoenergetic.
CHAPTER 1 Introduction to Radiation Protection
TEAM CONCEPT IN THE MEDICAL FIELD
In recent years, there has been an increasing awareness
of the value of a “team approach” to patient care. In
a team approach, various participants assume responsibility for their areas of expertise, and the importance
of communication throughout the team is emphasized.
The composition of the team will vary with the circumstances of the patient. It will include the physician of
record, nursing and other medical assistants, and any
specialty care physicians, including radiologists and
their support group. This support group consists of
radiologic technologists, radiologist assistants, and
medical physicists. The team may also include physical
therapists, respiratory therapists, dietary consultants,
language interpreters, and others. It is recognized that
each member of the team brings their own unique
contributions to a successful medical interaction with
the patient and that teamwork reduces the rate of
occurrence of medical errors. Such an organized
collaborative approach can also have the benefit of
increased radiation safety, both to patients and directly
involved members of the imaging team. This model is
becoming a standard part of the curriculum at all levels
of training for medical schools, residencies, and medical
professional training programs.
1–5
Organizations such
as The American Registry of Radiologic Technologists
(ARRT), The American Society of Radiologic Technologists (ASRT), and The Joint Commission encourage
health care providers to function as effective team members while establishing a culture of quality, patient
safety, and high reliability.
CONTROL OF RADIANT ENERGY
Target
(anode +)
Glass
envelope
X-ray beam
(electromagnetic
waves)
Fig. 1.1 Radiant energy is emitted from the x-ray tube in the
form of waves (or particles). This energy made by humans can
be controlled by the selection of equipment components and
devices made for this purpose and by the selection of appropriate technical settings.
High-speed
electron
stream
Filament
(cathode −)
By adhering to these good practices, technologists
and radiologists minimize the possibility of causing
damage to healthy biologic tissue.
3
By using the knowledge of radiation-induced hazards
that has been gained over many years and by employing
effective methods to limit or eliminate those hazards,
humans can safely control the use of “radiant energy.”
An example of controllable radiant energy is the radiation produced from an x-ray tube (Fig. 1.1).
Radiologic technologists and radiologists:
• Are educated in the safe operation of x-ray–producing
imaging equipment.
• Use protective devices whenever appropriate.
• Follow established procedures.
• Select technical settings that significantly reduce radiation exposure to patients and to themselves.
GOALS OF RADIATION PROTECTION
The goal of modern radiation protection programs is
twofold: to protect persons from both short-term and
long-term effects of radiation. Some of these effects
occur in just specific organs and organ systems. Others,
such as cancer and genetic changes, may affect the
whole body and future generations.
CONCEPT OF RADIATION PROTECTION
Diagnostic imaging professionals have an ongoing responsibility to ensure radiation safety during all medical
4
CHAPTER 1 Introduction to Radiation Protection
radiation procedures. They fulfill this obligation by
following an established radiation protection program.
Radiation protection may be defined simply as effective
measures employed by radiation workers to safeguard
patients, personnel, and the general public from unneces-
sary exposure to ionizing radiation. This refers to any
radiation exposure that does not benefit a person in
terms of diagnostic information obtained from images
for the clinical management of medical needs. Effective
protective actions take into consideration both human
and environmental physical determinants, technical
elements, and procedural factors. To comprehend that
process more fully, this textbook has been designed
to introduce its readers at appropriate times in the following chapters to the relevant scientific principles that
underlie the tools and techniques of these measures.
Scientific application of tools and techniques requires
a common usage of quantities and units. Important
examples of this are length and time with their corresponding metrics: meters, and seconds. Unfortunately,
there is not just one unique set or system of these units
for ionizing radiation. Rather, three such systems are
currently in existence, and each one has a significant area
of usage. Appendix A contains detailed lists of all the
major components comprising each of the three systems
and furthermore gives the numeric relationships among
the corresponding units of each system.
Introduction to Radiation Quantities and Units of Measure
The science of radiation quantities and units is complex.
An introduction is provided to allow the reader to
appreciate the relative magnitudes of sources of radiation exposure of humans to radiation. There are three
main types of quantities to consider:
• Exposure
• Absorbed dose
• Effective dose
A brief explanation of these quantities and the units
in which they are most commonly specified follows.
Exposure (coulomb per kilogram [C/kg] or milliroentgen [mR]). The terms exposure and exposed are used in
everyday speech to refer to any situation in which radiation is in contact with humans, as in “The patient was
exposed to radiation to obtain a medical image.” But
there is a specific scientific meaning to the term expo-
sure. Exposure is the amount of ionization produced in
air when ionizing radiation is present. The air at the
surface of an x-ray room tabletop or the interior of a
computed tomography (CT) scanner becomes ionized
when the x-ray tube is energized. Devices called ioniza-
tion chambers can measure this quantity directly and are
used to determine the amount of radiation
produced by x-ray equipment. Exposure is measured
in coulomb per kilogram (C/kg) in the metric International System of Units (SI), or historically and still quite
commonly in milliroentgens (mR), a subunit of the
roentgen, a nonmetric unit likewise used for measuring
the ionizing capability of radiation. A milliroentgen is
equal to 1/1000 of a roentgen.
Absorbed Dose (milligray [mGy]). The term dose
is also employed in everyday speech, as in “Everyone
receives a dose of radiation from sources in the environment.” The exact meaning of absorbed dose is the
amount of energy that is deposited in a material per
unit mass of the material. For living tissue more energy
deposited is usually related to more disruption of biomolecules. Less energy received is related to less disruption. Absorbed dose is measured in milligray (mGy), a
subunit of the gray (Gy) in the SI. The milligray is equal
to 1/1000 of a gray.
Effective Dose (millisievert [mSv]). The term effec-
tive dose is an attempt to provide a quantity that is
a measure of general harm in humans. It takes into
account the amount of absorbed dose that is received
by a human, the exact type of radiation (the effects
of alpha particles, beta particles, protons, and neutrons
are all somewhat different at the same absorbed dose
levels), and the specific organs or organ systems irradiated. The effective dose is the best overall measure of
the biologic effects of ionizing radiation. In SI units,
effective dose is specified in millisievert (mSv), a sub-
unit of the sievert (Sv). The millisievert is equal to
1/1000 of a sievert.
Need to Safeguard Against Adverse Biologic Effects of Ionizing Radiation
The need to safeguard against unnecessary radiation
exposure is based on strong evidence that living tissue
of animals and humans can be damaged by exposure to
ionizing radiation. This type of harm is referred to as
adverse biologic effects. In medicine, when radiation
safety principles are correctly applied during imaging
CHAPTER 1 Introduction to Radiation Protection
5
procedures, the energy deposited in living tissue by
radiation can be limited, thereby reducing the potential
for adverse biologic effects. This textbook focuses on
radiation protection for patients, diagnostic imaging
personnel, and the general public.
JUSTIFICATION AND RESPONSIBILITY FOR IMAGING PROCEDURES: BENEFIT VERSES RISK
Radiation exposure should always be kept at the lowest
possible level for the general public. However, when
illness or injury occurs or when a specific imaging
procedure for health screening purposes is called for,
a patient may choose to assume a relatively small statistical risk for a physician to obtain essential diagnostic
medical information. A prime example of such a voluntary assumption of risk occurs when women elect
to undergo screening mammography to enable detection of breast cancer in its early stages (Fig. 1.2). Highquality mammography continues to be the most
effective tool for diagnosing breast cancer early, when
the disease can best be treated.6 Its use contributes
significantly to improving the life expectancy for women
at risk. The potential benefits of this exposure to radiant
energy far outweigh any slight chance of inducing a radiogenic malignancy or any genetic defects.
Diagnostic Efficacy
Diagnostic efficacy is the degree to which the diagnos-
tic study accurately reveals the presence or absence
of disease in the patient, while adhering to radiation
safety guidelines. It is maximized when essential images
are produced with the least radiation exposure to the
patient. Thus this concept of efficacy is a vital part of
radiation protection in the healing arts, providing
the basis for deciding whether an imaging procedure
or practice is justified (Box 1.2). Ultimately, the referring physician, however, carries the responsibility for
determining this medical necessity for the patient. After
ordering an x-ray examination or procedure, the referring physician must accept basic responsibility for protecting the patient from nonuseful radiation exposure.
As health care professionals, radiographers also accept a
Fig. 1.2 High-quality mammography continues to be the most effective tool for diagnosing breast cancer.
It can be used as a screening tool or a diagnostic procedure. In either instance, the potential benefits of
exposure to radiant energy, in terms of medical information obtained, far outweigh any slight chance of inducing a radiogenic malignancy or any genetic defects. (From Long BW, Rollins JH, Smith BJ Merrill’s atlas of
radiographic positioning and procedures, ed 14, St. Louis: Elsevier; 2019.)
6
CHAPTER 1 Introduction to Radiation Protection
BOX 1.2 Achievement of Diagnostic
Efficacy
Imaging procedure
orpractice justified
by referring
physician
n
Minimal
radian ttion
exposure
P
rresence
orabsence
ofdisease
revealed
n
Optimal
image(s)
produced
Diagn5oostic
efficacy
portion of the responsibility for the patient’s welfare
by providing high-quality imaging services. Both the radiographer and the involved radiologist share in the
task of keeping the patient’s medical radiation exposure
at the lowest level possible. This can best be accomplished by producing optimal images with the first
exposure. Repeated examinations made necessary by
technical error or carelessness (Fig. 1.3) must be avoided.
AS LOW AS REASONABLY ACHIEVABLE (ALARA) PRINCIPLE
ALARA is an acronym for “as low as reasonably achiev-
able.” This term is synonymous with the term optimiza-
tion for radiation protection (ORP). The rationale
for ALARA or ORP comes from evidence compiled by
scientists over the past century.7 At the time of this publication, radiation protection guidelines remain rooted
in the philosophy of ALARA. Therefore this dictum, as
low as reasonably achievable, should be a main part of
every health care facility’s personnel radiation control
program. In addition, because at this time no firm dose
limits have been established for the amount of radiation
that patients may receive for each individual imaging
procedure, the ALARA philosophy should be maintained and must show that all reasonable actions that
will reduce doses to patients and personnel to levels that
are below those strictly required by regulations have
been employed (Fig. 1.4). Radiation-induced cancer
A B
Fig. 1.3 (A) Posteroanterior chest projection requiring repeat examination because of multiple external
foreign bodies (several necklaces and an underwire bra) that should have been removed before the x-ray
examination. (B) Anteroposterior projection of a right hip requiring a repeat examination because of poor collimation and the presence of an external foreign body (a cigarette lighter) overlying the anatomy of concern.
The patient’s slacks with the pocket containing the lighter should have been removed before the x-ray
examination.