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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5196_Библиотеки_им_академика_М_И_Перельмана.pdf
Management of Patient Radiation Dose
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.
• Explain the meaning of a holistic approach to patient
care and recognize the need for effective communication between imaging department personnel and the
patient.
• Discuss how to minimize or eliminate voluntary motion and how involuntary motion can be compensated
for during a diagnostic radiographic procedure.
• Discuss shielding concepts and identify anatomic
areas of the body that should be protected with
specific area shielding.
• Explain current patient gonadal shielding and fetal
shielding practices in diagnostic radiology and discuss the rationale for such practices with modern
digital x-ray equipment.
• Discuss the need to use appropriate radiographic
technical exposure factors for all radiologic procedures and show how these factors may be adjusted
to reduce patient dose.
• Explain how a radiographer can achieve a balance in
radiographic exposure factors to ensure the presence
of adequate information in the completed image
while minimizing patient dose.
• Clarify how adequate immobilization and correct
image postprocessing techniques reduce radiographic
exposure for the patient.
12
During X-Ray Procedures
• Compare the use of an air gap technique for specific
examinations with the use of a mid-ratio grid (8:1).
• Describe the benefits of repeat analysis programs.
• List six nonessential radiologic examinations and
explain why each is considered unnecessary.
• List four ways to indicate the amount of radiation
received by a patient from diagnostic imaging
procedures and provide details for each.
• Discuss the concept of fluoroscopically guided positioning and clarify why this is an unacceptable practice.
• Define the term genetically significant dose (GSD).
• Describe special precautions employed in radiography to protect the pregnant or potentially pregnant
patient during an x-ray examination.
• Discuss the protocol to be followed when irradiation of an unknown pregnancy occurs and explain
how the absorbed dose to the patient’s embryofetus is determined.
• Explain the reason children require special radiation protection when they undergo conventional
diagnostic imaging procedures.
• Pledge to Image Gently and Image Wisely.
• Explain the use of Dual Energy X-Ray Absorptiometry (DEXA, or DXA scan) for determining bone
loss by measuring bone mineral density (BMD)
and compare the radiation exposure of the patient
and radiographer with that of conventional x-ray
imaging and computed tomography.
C H A P T E R O U T L I N E
Effective Communication
Verbal Messages and Body Language
Importance of Patient Instructions
Appropriate Communication for Procedures
That Will Cause Pain or Discomfort
Repeat Radiographic Exposures Resulting
From Poor Communication
Immobilization
Need for Patient Immobilization
Types of Patient Motion
227
228
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
Protective Shielding
Need for Protective Shielding
Gonadal Shielding
Specific Area Shielding
Technical Exposure Factors
Appropriate Selection
Use of Standardized Technique Charts
Use of High-kVp and Low-mAs Exposure Factors
to Reduce Dose to the Patient
Postprocessing of the Radiographic Image
Quality Control Program
Air Gap Technique
Reduction of Scattered Radiation
High Peak Kilovoltage Radiography
Repeat Images
Consequence of Repeat Images
Increase in Repeat Rates
The Benefit of a Repeat Analysis Program
Concern About Risk of Exposure During Diagnostic
Imaging Procedures
Benefit Versus Risk
Nonessential Radiologic Examinations
Specifying the Amount of Radiation Received by a
Patient During a Diagnostic Imaging Procedure
Fluoroscopically Guided Positioning
Protecting the Pregnant or Potentially Pregnant Patient
Position of the American College of Radiology on Ab-
dominal Radiologic Examinations of Female Patients
Determining the Possibility of Pregnancy
Irradiation During an Unknown Pregnancy
Procedure to Follow and Responsibility for Absorbed
Equivalent Dose Determination to the Patient’s
Embryo-Fetus
Sample Case to Estimate Approximate Equivalent
Dose to the Embryo-Fetus
Sample Case to Obtain an Approximate Estimate
of the Fetal Equivalent Dose
Irradiating a Known Pregnant Patient
Pediatric Considerations During Radiographic
Imaging
Vulnerability of Children to Radiation Exposure
Children Require Smaller Radiation Doses Than
Do Adults
Patient Motion and Motion Reduction Methods
Gaining Cooperation During the Procedure
Collimation
Patient Protection in Computed Tomography for
Adults and Children: Similarities and Necessary
Changes
Image Gently Campaign
Image Wisely Campaign
Dual Energy X-Ray Absorptiometry (DEXA, or DXA
Scan)
Summary
K E Y T E R M S
air gap technique
Alliance for Radiation Safety
in Pediatric Imaging
bone marrow dose
dual-energy x-ray absorptiometry
(DEXA, or DXA scan)
effective communication
During a diagnostic x-ray procedure, a holistic approach
to patient care is essential. A holistic approach means
considering for treatment the whole person rather than
just the area of interest. Holistic patient care begins with
effective communication between the radiographer and
the patient. Effective communication is “an interaction
that produces a satisfying result through an exchange of
entrance skin exposure
fluoroscopically guided
positioning (FGP)
genetically significant dose
(GSD)
gonadal dose
Image Gently Campaign
Image Wisely Campaign
repeat image
scattered radiation
skin dose
thermoluminescent dosimeters
(TLDs)
information”1 and can be accomplished through verbal
messages, body language, and clear and concise instructions. This type of dialog alleviates the patient’s uneasiness and increases the likelihood of full cooperation and
successful completion of the procedure. To provide appropriate care for all patients, the radiographer should
develop easily understandable communication skills.
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
Radiographers must limit the patient’s exposure to
ionizing radiation by:
• Employing appropriate radiation reduction techniques
• Using protective devices, accurate positioning of the
body or body part, and techniques that minimize
radiation exposure
Patient exposure can be substantially reduced by:
• Use of proper body or body part immobilization and
other motion reduction techniques
• Proper x-ray beam limitation devices
• Adequate filtration of the x-ray beam
• Use of specific area shielding
• Selection of suitable technical exposure factors used in
conjunction with computer-generated digital images
• Use of appropriate digital image processing
• Elimination of repeat radiographic exposures
This chapter provides an expansive overview of
methods and techniques that radiographers can use to
minimize the patient’s exposure to radiation during
radiologic examinations.
EFFECTIVE COMMUNICATION
229
Verbal Messages and Body Language
When verbal messages and gentle body language, or
nonverbal messages, are understood as intended, communication between the radiographer and the patient is
effective. Good communication:
• Encourages reduction in anxiety and emotional
stress
• Enhances the professional image of the radiographer
as a person who cares about the patient’s well-being
• Increases the chance for successful completion of the
x-ray examination, thereby reducing the potential of
repeat exposures resulting from poor communication
Everyone within the imaging department should
always behave as a compassionate professional. Words
and actions must demonstrate understanding and
respect for human dignity and individuality.
Importance of Patient Instructions
Each encounter with a patient during a diagnostic x-ray
procedure should begin with clear and concise instructions (Fig. 12.1). When health care professionals do not
thoroughly explain procedures, patients fear the unknown and become anxious, especially during lengthy
examinations. To alleviate the problem, the radiographer
must take adequate time to explain the procedure in
simple terms that the patient can understand. Patients
Fig. 12.1 Clear, concise instructions promote effective com-
munication between the radiographer and the patient.
should also be given the opportunity to ask questions.
The radiographer must listen attentively to these questions and answer them truthfully in an appropriate tone
of voice and in accordance with ethical guidelines. This
creates a sense of trust between the patient and the
radiographer and encourages any further discourse.
Appropriate Communication for Procedures That Will Cause Pain or Discomfort
If the radiographic procedure will cause pain, discomfort, or any strange sensations, the patient must be fully
informed before the procedure begins (Fig. 12.2). However, to prevent the patient from imagining more pain
or discomfort than the procedure will cause, the radiographer should try not to overemphasize this aspect of
the examination.
Repeat Radiographic Exposures Resulting From Poor Communication
Repeat radiographic exposures can sometimes be attributed to poor communication between the radiographer
230
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
Fig. 12.2 Before the procedure begins, inform the patient of any pain, discomfort, or strange sensations that
they might experience during the procedure.
and the patient. Inadequate or misinterpreted instructions may prevent the patient from being able to cooperate as needed. For example, during an interventional
radiographic examination that creates some uncomfortable warmth, patients could move suddenly because
they are surprised or want to inform the technologist or
physician that something seems to be wrong. Such
physical movement usually results in a repeat period of
exposure. Effective communication between the radiographer and patient can prevent this problem from
occurring.
IMMOBILIZATION
Need for Patient Immobilization
If a patient moves during a radiographic exposure, the
radiographic image will be blurred. Because blurred
images have little or no diagnostic value, a repeat
examination is necessary, even though it results in additional radiation exposure for the patient. Proper
body or body part immobilization and the use of
motion reduction techniques can eliminate or at least
minimize any patient motion.
Types of Patient Motion
Patient motion may be classified as:
• Voluntary
• Involuntary
Voluntary motion would, under normal circumstances,
be expected to be controlled by the patient. Inability to
exercise such control may be attributed to:
• The patient’s advanced age
• Breathing problems or irregularities
• Increased anxiety
• Physical discomfort
• Fear of the examination
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
Shielding
device
Fig. 12.3 Adequate immobilization during radiographic exami-
nations eliminates or at least minimizes voluntary motion. This
restraint has a shield (left) that may be adjusted to protect the
child’s reproductive organs from radiation exposure when that
area of the body is not of clinical interest.
• Fear of unfavorable prognosis
• Mental instability
To eliminate voluntary motion during radiography,
the radiographer must gain the cooperation of the patient or adequately immobilize that individual during
the radiographic exposure (Fig. 12.3). Various suitable
restraining devices are available to immobilize the whole
body or the individual body part to be imaged. These
aids should be used whenever necessary. Involuntary
motion, caused by muscle groups such as those associated with the digestive organs or the heart, cannot be
willfully controlled. Other clinical manifestations also
cause involuntary motion. These include:
• Chills
• Tremors such as those experienced by patients with
Parkinson’s disease
• Muscle spasms
• Pain
• Active withdrawal
Decreasing the exposure time with an appropriate
increase in milliamperes (mA) to maintain sufficient
231
milliampere-seconds (mAs) for useful radiographic
brightness (the amount of luminance of an image on a
display monitor) and using very-high-speed imaging
receptors can, to a high degree, compensate for involuntary motion.
PROTECTIVE SHIELDING
Need for Protective Shielding
The potential for radiation exposure to the radiosensitive body organs and tissues of a patient requires the
use of precise patient positioning and, in many cases,
personal shielding (i.e., a device made of lead or leadimpregnated materials that will adequately attenuate
ionizing radiation) to reduce or eliminate a radiation
dose that could otherwise result in biologic damage.
Areas of the body that should be shielded from the
useful beam whenever possible are the:
• Lens of the eye
• Breasts
• Thyroid gland
Gonadal Shielding
After some decades of experience with modern digital
x-ray equipment and as a result of improvements in
dosimetry estimates of the efficacy of shielding with
modern equipment and techniques, professional and
scientific societies are modifying shielding practices in
diagnostic radiology.
In April of 2019, the American Association of Physicists in Medicine (AAPM) issued a position statement
regarding the use of patient gonadal shielding and fetal
shielding (Policy PP32-A). The statement indicated
that patient gonadal shielding and fetal shielding during diagnostic imaging procedures should be discontinued as routine practice (AAPM, 2019). The statement is based on research indicating that patient
shielding may jeopardize the benefits of the radiologic
examination. Specifically, when a lead shield is placed
incorrectly within the collimated x-ray beam and automatic exposure control is used, the lead shield may obscure anatomic information or interfere with the automatic exposure control system. Furthermore, these
effects may compromise the diagnostic efficacy of the
examination or increase the patient’s radiation dose
because of the attenuation characteristics of the shield.
Because of these risks and the statistically seen minimal
to nonexistent benefit associated with fetal and gonadal
232
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
Fig. 12.4 (A) Adequate and precise collimation of the radiographic beam must always be the first step in
gonadal protection. (B) When the gonads are not in the area of clinical interest, precise collimation of the
radiographic beam reduces gonadal exposure. (From Lampignano J, Kendrick LE: Bontrager’s textbook of
radiographic positioning and related anatomy, ed 10, St. Louis, 2021, Elsevier.)
shielding, AAPM now recommends that the use of
shielding should be discontinued.2 Since the AAPM statement, many organizations have supported the position
statement, including thre NCRP, ACR, ASRT, and ARRT.
Adequate collimation of the radiographic beam, to
include only the anatomy of interest (Fig. 12.4), must
always be the first step in gonadal protection.
CARES Committee. Subsequent to ther publication
of ther AAPM position statement, and as a response to
radiologic technologists’ and radiologic science educators, the AAPM has formed the CARES (Communicating Advances in Radiation Education for Shielding)
Committee. This group includes members from more
than 14 professional organizations worldwide, representing medical and health physicists, radiologic technologists, and organizations that oversee educational
programs for radiologic technologists, radiologists, and
state regulators. CARES’ purpose is for all stakeholders
to educate the profession regarding the AAPM gonadal
shielding position statement. It is of the utmost importance that the shield is not to any degree located within
the collimated area of exposure because if AEC is used,
it will not allow the exposure to terminate because it
attempts to penetrate the lead shield.
Specific Area Shielding
Radiosensitive organs and tissues may be selectively
guarded against the primary beam during a diagnostic
radiographic examination. Shields for the lens of the
eye are the contact type and are positioned directly on
the patient.3 They can reduce or eliminate exposure to
that highly sensitive area.
TECHNICAL EXPOSURE FACTORS
Appropriate Selection
The selection of scientifically correct technical exposure
factors for each x-ray examination is essential to ensure
a useful diagnostic image with minimal patient dose. A
high-quality image has sufficient brightness to display
anatomic structures, an appropriate level of subject
contrast to differentiate among such structures, the
maximum amount of spatial resolution,* and a minimal amount of distortion. Limiting the amount of
*Spatial resolution is the recorded detail in the radiographic
image.
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
233
BOX 12.1 Technical Exposure Factor
Considerations
• Mass per unit volume of tissue of the area of clinical
interest
• Effective atomic numbers and electron densities of
the tissues involved
• Type of image receptor
• Source-to–image receptor distance (SID)
• Type and quantity of filtration employed
• Type of x-ray generator used
• Balance of radiographic brightness required
quantum noise, or mottle,* caused when too few
x- rays reach the image receptor, is a concern.4 The appropriate technical factors are determined by considerations such as those listed in Box 12.1.
Use of Standardized Technique Charts
When a properly calibrated AEC system is not employed
to obtain a uniform selection of x-ray exposure factors,
well-managed imaging departments make use of standardized technique charts that have been established for
each x-ray unit. As was discussed in the previous chapter,
a digital image receptor is capable of responding to a
large variation in x-ray exposures, after which a modern
computer processing system can produce acceptable images, even when significant overexposure has occurred.
This raises an important radiation safety issue in that
unnecessarily high radiation exposure levels could result
in medical images of acceptable image quality such that
patient overexposure may not be noticed. Because of
this, the standardization of technique charts has become
even more critical. Radiology departments cannot rely
on vendors and other agencies to set technical standards.
Establishing and validating protocols with the aid of
their quality assurance team helps radiology departments ensure consistency in the diagnostic quality of
their digital examinations and minimizes the potential
for exposure technique selection errors.
The radiographer is responsible for consulting an
available standardized technique chart before making
4
each radiographic exposure to ensure an acceptable diagnostic image is acquired using exposure factors that
yield minimal patient dose. Neglecting to use such technique charts necessitates estimating the technical exposure factors, which may result in:
• Poor-quality images
• Repeat examinations
• Additional and unnecessary exposure to the patient
Systematizing exposure techniques, however, does
not mean that radiographers use the same protocol for
all patients in all situations. Exposure techniques must
be adjusted for patients’ specific conditions and history.
Proper and consistent use, however, of applicable exposure technique charts, adequate peak kilovoltage (kVp),
and a well-calibrated AEC are all essential to producing
quality diagnostic images consistently while minimizing
patient radiation exposure.
4
Use of High-kVp and Low-mAs Exposure Factors to Reduce Dose to the Patient
Technique factors that minimize the radiation dose to
the patient should be selected whenever possible. The
use of higher kVp permits lower mAs settings, which
reduces patient entrance dose (Fig. 12.5A, B). In digital
imaging, the amount of exposure (related to the mAs
setting) reaching the digital image does not directly
affect the amount of brightness produced, because of
computer processing. Adequate penetration of the anatomic part, which is kVp dependent, is needed to create
the differences in x-ray intensities exiting the part relative to adjacent structures to produce the desired level of
contrast. As long as the part is adequately penetrated,
increasing kVp by 15% with a corresponding decrease in
mAs reduces patient exposure significantly while yielding satisfactory image quality. The radiographer must
always seek to achieve a balance in technical radiographic exposure factors to:
• Ensure the presence of adequate information in the
acquired image
• Minimize patient dose (see Fig. 12.5C)
POSTPROCESSING OF THE RADIOGRAPHIC IMAGE
*Quantum noise, or mottle, is a blotchy radiographic image
that results when an insufficient quantity of x-ray photons
reaches the image receptor.
When digital images are acquired, correct image
postprocessing is essential to produce a high-quality
diagnostic image. For this, any artifacts produced by
234
High kVp, low mAs Low kVp, high mAs
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
X-ray tube
High-energy,
penetrating
x-ray beam
Small absorbed
A B
dose
75 kVp
16 mAs
100 kVp
4.5 mAs
Good chest radiograph
Good chest radiograph*
*Reduces patient exposure by 70%
C
Fig. 12.5 The use of higher kilovoltage (kVp) and lower milliamperage and exposure time in seconds (mAs)
reduces patient dose. (A) The use of high kVp and low mAs results in a high-energy, penetrating x-ray beam
and a small patient-absorbed dose. (B) The use of low kVp and high mAs results in a low-energy x-ray beam
of greater intensity, the majority of which the patient will easily absorb. (C) Example of a higher kVp, lower
mAs technique resulting in a 70% reduction in patient exposure without significantly compromising radiographic quality.
Low-energy,
x-ray beam
Large absorbed
dose
the image receptor, software, or patient-related problems must be controlled. Artifacts are unwanted densities in the image that are not part of the patient’s
anatomy and may negatively affect the ability of a radiologist to interpret the image correctly. Failure to
eliminate these defects, or at least to reduce them significantly, can result in an unacceptable digital image
and can, therefore, necessitate a repeat examination,
thus increasing patient dose.
Quality Control Program
To ensure quality control in the acquiring and
processing of digital images, it is indispensable that
every imaging department establishes a quality control
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
235
program that includes regular monitoring and maintenance of all processing and image display equipment in
the facility. Such a program will promote quality assurance by decreasing the likelihood of producing suboptimal- quality images, repeat exposures, unnecessary
absorbed patient dose, and incorrect x-ray projections.
Radiographers are the operators of sophisticated
imaging equipment and therefore are the individuals
who may first recognize any equipment malfunction.
Problems that occur in digital imaging (either computed radiography [CR] or digital radiography [DR])
tend, unfortunately, to be systematic, which can affect
the quality of every image and the degree of radiation
exposure of every patient until these problems are
identified and corrected. Mandated full acceptance
testing of new equipment, regular calibration and
performance evaluation of existing equipment, and
proactive and consistent image review quality control
can prevent these systematic errors.4 QC programs
documentation should include step-by-step procedures for performance, monitoring, and continuing
quality control.
3–8
AIR GAP TECHNIQUE
Reduction of Scattered Radiation
The air gap technique is an alternative procedure to use
in place of a radiographic grid for reducing scattered
radiation during specific examinations (e.g., cross-table
lateral projection of the cervical spine, areas of chest
radiography). This technique works by using an increased object-to-image receptor distance (OID). Less
scatter radiation at the detector decreases image blurring and thereby improves radiographic image contrast.
If magnification is not desired, a corresponding increase in source-to-image receptor distance (SID) may
be made.
To perform the air gap technique, the image receptor
is placed 10 to 15 cm (4 to 6 inches) from the patient,
and the x-ray tube is positioned approximately 300 to
366 cm (10 to 12 feet) away from the image receptor.
The scattered x-rays from the patient are disseminated
in many directions at acute angles to the primary beam
when the radiographic exposure is made. Because of the
increased distance between the anatomic structures being imaged and the image receptor, a higher percentage
of the scattered x-rays produced is less likely to strike
the image receptor (Fig. 12.6). This air gap method
effectively provides an adequate grid-type scatter
cleanup effect. In general, the use of an air gap technique requires the selection of technical exposure factors that are comparable to those used with an 8:1 ratio
grid. Therefore, when a patient dose is compared with a
non-grid technique, it is higher, but when compared
with the patient dose resulting from the use of a midratio grid (8:1), the dose from an air gap technique is
about the same.
High Peak Kilovoltage Radiography
In high-kVp radiography that employs kVp settings of
90 or above, air gap techniques are, for the most part,
not as effective. Still, some facilities that perform chest
radiography by using kVp settings of 120 to 140 do successfully use air gap techniques. In general, when x-rays
are scattered through greater angles, such as occurs for
images produced at less than 90 kVp, air gap techniques
are more successful.
REPEAT IMAGES
Consequences of Repeat Images
A repeat image is an image that must be performed
more than once because of human or mechanical error
during the production of the initial image. This additional imaging, unfortunately, increases patient dose. If
the patient’s gonads were included in the imaged area,
then the gonads would have received a double dose of
radiation. Occasionally, an additional image is permissible when it is recommended by the radiologist to
obtain additional diagnostic information. However, repeat exposures resulting from carelessness or poor
judgment on the part of the radiographer must be
eliminated. The radiographer should, from the beginning of the examination:
• Correctly position the patient
• Select the appropriate technical radiographic exposure
factors that will ensure the production of optimalquality images
Increase in Repeat Rates
Repeat rates for previously film-based radiology departments were documented to be in the range of 10%
to 15%, and their leading cause was attributed to the
use of incorrect technical factors. With the advent of
236
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
Usual film position
Wide-angle scattered
x-rays do not strike the
image receptor
Image receptor position
for air gap
Many of the scattered x-rays have such low
energy that they are absorbed by the air
and do not even reach the image receptor.
Fig. 12.6 The air gap technique. (From Radiobiology and radiation protection: Mosby’s radiographic instructional
series, St. Louis, 1999, Elsevier.)
digital imaging, it was expected that repeat rates would
decrease to zero because digital equipment imaging
systems can correct errors related to technical factors.
A series of research studies, however, have reported
repeat rates in many digital departments at approximately 5%, and some, unfortunately, at the same rate
as for the earlier film-screen systems’ departments.
Some studies have even demonstrated repeat rates as
high as 17%. Digital imaging significantly changed the
cause of repeated images, shifting from exposurerelated to positioning errors. The unexpected increase
in repeat rates has in many instances been ultimately
attributed to the trifling ease of retaking an exposure
in direct DR. Since there is no imaging receptor to be
further processed as in CR and film-screen radiography, the image can be repeated quickly with a modification in the patient’s positioning. Some radiographers often strive for a perfect image, even when the
initial image would be deemed acceptable.9 Repeating
an exposure to improve an already acceptable image is
unnecessary and will only increase patient radiation
dose needlessly.
The Benefits of a Repeat Analysis Program
Health care facilities can gain significantly by implementing and maintaining a repeat analysis program. Repeat
analysis is particularly critical in CR and DR. In these
modalities repeating exposures because of improper
technique is not usually necessary. In digital imaging,
overexposed or underexposed images can be adjusted by
computer to appear technically acceptable. Consequently,
it is essential for the delivery of nonexcessive patient exposures that a qualified medical physicist makes exposure
measurements for the techniques employed at the site to
ensure that they are within acceptable ranges. With CR or
DR, it is necessary to develop a policy whereby the digital
files that correspond to retaken images can be recovered
for analysis, since this would not happen automatically.
Analysis of a department’s repeat rate:
• Provides valuable information for process improvement
• Helps minimize patient exposure
• Improves the overall performance of the department
Some categories for unacceptable images are listed in
Box 12.2.
4