CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Medical Physicist’s Role
n
n
Personnel Protection During
Fluoroscopic Procedures
n
n
n
Beth Schueler
Mayo Clinic
Rochester, Minnesota
n
n
Procedure room design
Movable and personal shielding device selection
Fluoroscopic equipment selection
Fluoroscopic system optimization
Personnel exposure monitoring
Personnel exposure investigation
Radiation safety training
2
Learning Objectives
n
n
n
Stray Radiation Sources
What is the nature of stray radiation in
fluoroscopic procedures?
What can be done to reduce occupational
exposure?
What regulations must be followed regarding
personnel radiation exposure?
n
n
X-ray tube leakage
Scatter from patient
and objects exposed
to the primary beam
3
4
X-Ray Tube Leakage
Part 1020.30 (k) Leakage radiation from the
diagnostic source assembly:
n
n
n
not to exceed 100 mR/hr (0.88 mGy/hr) at 1 m
measured at
maximum kVp
(125-150 kVp) and
maximum continuous
mA (3-5 mA)
n
5
Beth Schueler, AAPM Annual Meeting 2003
Leakage radiation is
negligible compared
to scatter
typical amount of
leakage radiation for
fluoroscopy of an
average adult
abdomen:
5 mGy/hr at 1 m
1
0.8
mGy/hr at 1 m
n
X-Ray Tube Leakage
0.6
0.4
0.2
0
70
80
90
100 110 120
kVp
6
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
n
Scatter vs Field Size
Number of scattered x-rays depends on
n
the patient entrance skin exposure rate
n the patient entrance skin area
n the beam energy
n
n
For constant entrance
exposure rate and
constant kVp, scatter is
proportional to the
exposure field size
Typical scatter value
10
8
Scatter (mGy/hr)
Scatter
0.1% of incident exposure at 1 m for a 23-cm FOV
n for an entrance skin exposure rate of 20 mGy/min,
scatter at 1 m is 20 mGy/min or 1.2 mGy/hr
n
6
4
2
0
0
100
200
300
400
2
Field Size (cm )
7
8
For constant field size
and constant kVp, scatter
is proportional to the
entrance skin exposure
rate
n
10
Scatter (mGy/hr)
n
Scatter vs DAP
8
6
For constant kVp, scatter
is proportional to the
dose-area-product rate
(DAP)
4
2
0
0
20
40
60
10
8
Scatter (mGy/hr)
Scatter vs Entrance Exposure
6
4
2
0
80
0
Entrance Skin Exposure Rate
(mGy/min)
2
10
Scatter vs kVp
Scatter: Distribution
n
10
8
Scatter (mGy/hr)
For constant field size and
constant entrance skin
exposure rate, scatter
increases with kVp
6
Scatter intensity is
higher on the entrance
side of the exposed
volume
n
4
2
n
0
60
6
2
9
n
4
DAP Rate (Gy-cm /min)
80
100
120
primary beam most
intense on the entrance
side
forward scatter is
heavily attenuated
kVp
11
Beth Schueler, AAPM Annual Meeting 2003
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Stray Radiation: Horizontal Profile
Scatter: Distribution
n
n
The entrance skin port should be considered the
major radiation source for occupational
exposure
For actual imaging situations, the scatter
distribution is also affected by
0.25 mGy/hr
84
attenuation from unexposed tissue to the side
attenuation from the table and pad
n shielding by image intensifier, equipment supports,
lead shielding devices
2
1
0.5
n
n
1m
13
Stray Radiation: Vertical Profile
Learning Objectives
180
180
n
0.25
Distance From Floor (cm)
0.5
120
120
34 cm
1.0 mGy/hr
90
90
2.0
4.0
60
60
8.0
30
60
90
150
Patient120
entrance skin
Distance
dose From
= 87 mGy/min
Central Ray (cm)
0
30
60
90
120
150
Distance from Central Ray (cm)
Distance from Floor (cm)
150
150
n
n
What is the nature of stray radiation in
fluoroscopic procedures?
What can be done to reduce occupational
exposure?
What regulations must be followed regarding
personnel radiation exposure?
30
30
180
0
180
15
16
Radiation Safety: Operator
Occupational Exposure Reduction
n
n
n
What can operators do?
What can assisting personnel do?
What can medical physicists do?
n
use short taps of fluoro instead of continuous
exposure
n use 5-min fluoro-on time warning to maintain
awareness of total fluoroscopy time
n utilize last-image-hold for image study, discussion
and teaching
n develop workflow procedures with ancillary
personnel so that there is no fluoroscopic exposure
when they need to be close to the patient
n
17
Beth Schueler, AAPM Annual Meeting 2003
Minimize fluoroscopy beam-on time
18
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Radiation Safety: Operator
n
Radiation Safety: Operator
Increase distance from
the patient
n
Remove the grid when possible
reduces patient entrance skin exposure and scatter
by about a factor of 2
n reduction in image contrast is minimal for
n
GI: “spoon” palpation
device
n vertebroplasty: PMMA
injection device
n other interventional
devices: forceps
n
n
n
small patients and body parts
procedures requiring a large separation between the
patient and image intensifier
19
20
Radiation Safety: Operator
Lateral Projection: Tube by Operator
90
n
Position yourself on the x-ray beam exit side of
the patient when possible
Scatter at a height
of 100 cm
0.25 mGy/hr
60
0.5
30
Scatter intensity is lower on the image intensifier side
as compared to the x-ray tube side
n For C-arm fluoroscopy,
n
n
n
Distance from
0 Table Center
(cm)
30
frontal projections: place the x-ray tube under the table
lateral and oblique projections: place the x-ray tube on
opposite side of the patient
8.0
60
4.0
2.0
90
1.0 mGy/hr
0.5
Distance from
Central Ray (cm) 0
21
Scatter at a height
of 100 cm
n
60
4.0
90
120
150
120
180
22
90
1.0 mGy/hr
2.0
8.0
60
Radiation Safety: Operator
Lateral Projection: Tube Opposite Operator
0.5
30
Collimate tightly to the area of interest
reduces the entrance skin exposure area
improves image contrast
n entrance skin exposure may increase
n scatter will decrease with collimation as long as there
is a decrease in DAP rate
n similar result for wedge-shaped beam filters
n
30
n
Distance from
0 Table Center
(cm)
30
60
0.25 mGy/hr
90
Distance from
Central Ray (cm) 0
30
60
90
120
150
120
180
23
Beth Schueler, AAPM Annual Meeting 2003
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Radiation Safety: Operator
10
20
8
18
6
16
4
14
2
12
0
10
0
400
300
200
100
ESER (mGy/min)
Scatter (m G y/hr)
D AP (G y-cm 2 /m in)
Scatter vs Field Size
n
n
DAP
General imaging guidelines
place the x-ray tube as far as possible from the patient
place the II as close as possible to the patient
n use magnification modes sparingly
n
n
n
Adherence to these guidelines
reduces patient entrance skin exposure
increases spatial resolution
n decreases scatter, but only when collimation is used
n
n
Entrance Skin Field Size (cm 2 )
Scatter
Use optimal imaging chain geometry
n
Use DAP rate as a guide to estimate scatter
ESER
25
26
X-Ray Tube Positioning
ESER
(mGy/min):
DAP rate
22
18
Image Intensifier Positioning
(Gy-cm2/min):
4.8
4.8
4.3
(mGy/hr):
6.3
6.1
5.2
Scatter rate
ESER
36
18
20
(Gy-cm2/min):
5.3
4.6
2.9
(mGy/hr):
6.6
6.5
3.6
(mGy/min):
18
DAP rate
Scatter rate
27
Magnification Mode Selection
28
Radiation Safety: Operator
n
Use movable shielding
devices
ceiling-suspended shield
tableside shield
n undertable shield
n
n
ESER
20-cm FOV
28-cm FOV
28-cm FOV
35
18
20
(Gy-cm2/min):
4.5
4.6
2.7
(mGy/hr):
6.4
6.5
3.8
(mGy/min):
DAP rate
Scatter rate
Beth Schueler, AAPM Annual Meeting 2003
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30
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Scatter Levels without Shielding
Scatter Levels with Undertable Shielding
180
180
60
60
90
120
150
Distance From
Central Ray (cm)
0
30
60
90
120
150
n
90
90
60
60
30
30
0
31
30
60
90
120
Distance From
Central Ray (cm)
60
90
120
150
30
180
150
0
180
32
Distance from Central Ray (cm)
Occupational Exposure Reduction
n
120
4.0
Distance from Central Ray (cm)
n
120
1.0 mGy/hr
2.0
30
30
180
0
180
Distance from
FromFloor
Floor(cm)
(cm)
Distance
90
90
4.0
150
0.5
120
120
2.0
150
0.25
Distance From Floor (cm)
Distance
from Floor (cm)
0.5
1.0 mGy/hr
60
180
150
150
0.25
30
180
Radiation Safety: Assisting Personnel
What can operators do?
What can assisting personnel do?
What can medical physicists do?
n
Make sure you are aware of
beam-on cues
n
Increase your distance from
the patient when possible
Use movable shielding devices
n
n
warning lights, audio warnings
33
Average-Size Patient
Radiation Safety:
Operator and Assisting Personnel
180
180
Be aware that scatter is significantly higher for
large patients as compared to small patients
150
150
0.25
120
120
entrance skin exposure rate and kVp increases,
resulting in higher scatter rates
n image quality decreases, beam on-time may also
increase
n
0.5
24 cm
1.0 mGy/hr
90
90
2.0
60
60
30
60
90
120
150
30
30
180
150
0
180
Distance From
Central Ray (cm)
0
35
Beth Schueler, AAPM Annual Meeting 2003
Distance From Floor (cm)
Distance
from Floor (cm)
n
34
30
60
90
120
Distance from Central Ray (cm)
36
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Moderately Large-Size Patient
Large-Size Patient
180
180
180
180
0.25
150
150
120
120
2.0
90
90
4.0
60
60
30
60
90
120
150
Distance From
Central Ray (cm)
0
30
60
90
0.5
120
150
120
120
34 cm
0
180
60
60
8.0
30
60
90
120
150
30
30
180
150
0
180
Distance From
Central Ray (cm)
0
37
30
60
90
120
Distance from Central Ray (cm)
38
Personal Shielding Devices
Select appropriate personal shielding devices
n
90
90
2.0
Radiation Safety:
Operator and Assisting Personnel
n
1.0 mGy/hr
4.0
30
30
180
Distance from Central Ray (cm)
Distance From Floor (cm)
Distance
from Floor (cm)
0.5
1.0 mGy/hr
29 cm
150
150
Distance From Floor (cm)
Distance
from Floor (cm)
0.25
n
Proper fit is critical
n
Protective aprons
lead equivalent thickness of 0.5 mm recommended,
required in some states
n wrap-around style needed if side or back faces exposed
patient volume
n light-weight lead replacements (composites of materials
such as barium, tungsten) reduce total weight by 20-30%
n
n
n
if 2 layers are needed
to meet 0.5 mm leadequivalent
requirement, make
sure overlap is
sufficient
arm holes should not
be too wide
neck line should not
fall too low
39
40
Personal Shielding Devices
n
Personal Shielding Devices
Thyroid shields
n
use recommended if monthly collar badge reading
exceeds 4 mSv
n significantly reduces effective dose with minimal
inconvenience
n
n
Leaded glasses
n
use recommended if monthly collar badge reading
exceeds 4 mSv
n side shields needed since user does not typically face
the exposed patient volume
n
41
Beth Schueler, AAPM Annual Meeting 2003
Leaded gloves
0.5 mm lead equivalent shielding recommended if
hands must be in the primary beam
n leaded surgical gloves provide partial shielding (3040% attenuation) if hands are in high scatter area
n
provide minimal protection if hands are in the primary
beam: ABC drives up dose rate, protection on one side
only
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Radiation Safety: Physicist
Occupational Exposure Reduction
n
n
n
What can operators do?
What can assisting personnel do?
What can medical physicists do?
n
When constructing or remodeling a fluoroscopic
suite, ensure appropriate room design features
are incorporated
ample procedure room size
ample control room size
n large viewing windows
n intercom system between procedure room and
control room
n patient table and control area positioned so that no
straight-line scatter reaches
n
n
43
44
Room Design Features
n
n
Operator should be able to view all procedure room
entrances from expected operating position
Adequate structural shielding in walls, doors, and
windows
n
n
Radiation Safety: Physicist
n
n
consider structural shielding in procedure rooms where
mobile C-arms are used routinely
Movable shielding devices
n
Ensure fluoroscopic equipment radiation safety
design features are considered when specifying a
system for purchase
ceiling-mounted shields should be included with fluoroscopic
equipment installation
R&F systems: undertable x-ray tube configuration
results in lower personnel exposure as compared to
an overtable x-ray tube configuration (for nonremote applications)
45
R&F System: Undertable X-Ray Tube
46
R&F System: Overtable X-Ray Tube
180
180
180
150
150
150
4.0
Distance From Floor (cm)
Distance
from Floor (cm)
0.5
8.0
2.0
120
120
1.0 mGy/hr
2.0
4.0
90
90
60
120
1.0 mGy/hr
90
60
0.5
60
30
30
0
30
60
60
90
120
Distance From
Central Ray (cm)
90
120
Distance from Central Ray (cm)
150
30
180
150
0
180
Distance from Floor (cm)
0.25
30
0.25
47
Beth Schueler, AAPM Annual Meeting 2003
0
30
60
90
120
Distance from Central Ray (cm)
150
0
180
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Equipment Design Features
n
n
Equipment Design Features
Undertable x-ray tube
R&F systems (with
lead II tower drapes
attached) are preferable
to C-arm
configurations
For biplane systems, a
lateral C-arm that can
be positioned with the
II toward the operator
is desirable
n
Imaging chain components that allow
positioning for optimal geometry
II can be moved close to the patient
eliminate spot-film device if not needed
n x-ray tube located far from the patient
n
n
n
n
n
Removable or retractable grid
Last-image hold and fluoroscopy frame grab
Graphic collimator and wedge filter position
indicators on last-image hold
49
50
Equipment Design Features
n
Equipment Design Features
Low dose fluoroscopy settings available
n
pulsed fluoroscopy at 15, 7.5 and lower frames per
second
n image processing: video frame averaging
n use of spectral beam filtration
n
n
n
n
n
n
Variable rate digital image acquisition available
Patient dose indication available to the operator
Digital acquisition zoom
Low attenuation tabletop and pad
Visible exposure warning lights
Method to disable the fluoroscopy foot pedal to
eliminate inadvertent exposure during patient
removal or prep
51
52
Learning Objectives
Radiation Safety: Physicist
n
Implement and maintain a comprehensive
quality control program
n
work with vendor representatives and operators to
find optimal image processing and dose settings to
meet clinical imaging needs
n perform regular fluoroscopic equipment
performance and radiation safety evaluation
n perform personal protection device evaluation
n
n
n
53
Beth Schueler, AAPM Annual Meeting 2003
What is the nature of stray radiation in
fluoroscopic procedures?
What can be done to reduce occupational
exposure?
What regulations must be followed regarding
personnel radiation exposure?
54
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
Maximum Permissible Doses
n
Personal Dosimetry
Effective dose (whole body)
n
Annual: 50 mSv
n Cumulative: 10 mSv ´ age in years
n
n
n
n
Equivalent dose (partial body)
n
n
n
Single- and dual-monitor methods
single: above protective apron at collar level
dual:
n
n
Lens of eye: 150 mSv
Skin, hands, feet: 500 mSv
n
Embryo-fetus: 0.5 mSv/month
Monitor 1. above protective apron at collar level
Monitor 2. under protective apron at waist level
For the dual-monitor method, badges can easily
be inadvertently switched
n
color coding of badges is helpful
55
56
Dose Assignment
n
n
Dose Assignment
Individual state regulations vary
CRCPD Suggested State Regulations:
n
for single-monitor, HE = collar reading, or
if single-monitor reading > 25% of the dose limit,
HE = 0.3 ´ collar reading, or
n for dual-monitor,
HE = 1.5 ´ waist reading + 0.04 ´ collar reading
n
n
n
NCRP Report No. 122 “Use of Personal
Monitors to Estimate Effective Dose Equivalent
and Effective Dose to Workers for External
Exposure to Low-LET Radiation” 1995
n
n
for single-monitor, E = deep dose reading/21
for dual-monitor,
E = 0.5 ´ waist reading + 0.025 ´ collar reading
n
HE = effective dose equivalent
E = effective dose
57
58
Pregnant Workers
n
n
Dose limits apply only after written declaration of
pregnancy
Conceptus dose assignment method
n
n
n
Pregnant Workers
n
n
varies with individual state regulations
common method is to wear a monitor under the apron at the
waist level
estimate projected conceptus dose as 10% of collar badge for
0.5 mm lead-equivalent apron
n
n
if pregnancy planned, monitor under-apron
abdominal exposure prior to pregnancy
Protection
0.5 mm lead-equivalent aprons are sufficient
wrap-around styles critical if back may face radiation
source
n specially-designed maternity aprons available
n
n
Prediction of conceptus dose
n
Prediction of conceptus dose
Reference: Wagner and Hayman, Radiology 1982: 145: 559
59
Beth Schueler, AAPM Annual Meeting 2003
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CE: Quality Assurance Fluoroscopy 4, TH-B24A-1
References
·
American Association of Physicists in Medicine, “Managing the Use of
Fluoroscopy in Medical Institutions.” AAPM Report No. 58. Madison, WI:
Medical Physics Publishing, 1998.
·
Balter, S. Interventional Fluoroscopy. John Wiley and Sons (2001).
·
Balter S. “Staff Safety in the Interventional Fluoroscopic Laboratory” in
Intravascular Brachytherapy – Fluoroscopically Guided Interventions.
Stephen Balter, Rosanna C. Chan, Thomas B. Shope, Jr (eds.). AAPM
Monograph No. 28. Proceedings of the 2002 Summer School. Madison, WI:
Medical Physics Publishing, pp. 137-163, 2002.
·
Brateman L. “Radiation safety considerations for diagnostic radiology
personnel.” Radiographics 1999; 19:1037-1055.
·
Geise RA and Hunter DW. “Personnel exposure during fluoroscopy
procedures.” Postgraduate Radiology 1988; 8:162-173.
·
International Commission on Radiological Protection. Avoidance of Radiation
Injuries from Medical Interventional Procedures. ICRP Publication 85. Ann
ICRP 2000; 20(2).
·
Marshall NW and Faulkner K. “The dependence of the scattered radiation
dose to personnel on technique factors in diagnostic radiology.” Med Phys
1996; 23:1271-1276.
·
National Council on Radiological Protection and Measurements (NCRP).
NCRP Report No. 105. “Radiation Protection for Medical and Allied Health
Personnel.” Bethesda, MD: NCRP, 1989.
·
National Council on Radiological Protection and Measurements (NCRP).
NCRP Report No. 122. “Use of Personal Monitors to Estimate Effective Dose
Equivalent and Effective Dose to Workers for External Exposure to Low-LET
Radiation.” Bethesda, MD: NCRP, 1995.
·
Wagner LK and Archer BA. Minimizing Risks from Fluoroscopic X-rays –
Bioeffects, Instrumentation and Examination (2nd ed.). Houston, TX:
Partners in Radiation Management (1998).
·
Wagner LK and Hayman LA. “Pregnancy and women radiologists.” Radiology
1982; 145:559-562.
·
World Health Organization. Efficacy and Radiation Safety in Interventional
Radiology. Geneva (2000).
Beth Schueler, AAPM Annual Meeting 2003