Transcript Radiation Safety Training for Fluoroscopy in Research Radiation Safety Office Indiana University Purdue University Indianapolis and Associated Facilities.

Radiation Safety
Training
for Fluoroscopy in
Research
Radiation Safety Office
Indiana University Purdue University Indianapolis
and Associated Facilities
Radiation Safety Concerns
in Fluoroscopy
 Monitor radiation exposure of operators
 Keep exposures “as low as reasonably
achievable” (ALARA)
 Minimize deleterious effects to subjects
from radiation exposure
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Radiation Quantities & Units
Exposure
(Air Kerma)
Absorbed
Dose
Dose
Equivalent
Traditional
Units
R or mR
SI Units
rad or mrad
Gy or mGy
rem or mrem
Sv or mSv
c/kg
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Radiation Quantities & Units
 Conversions - Traditional to SI Units
 1 R = 2.58 x 10-4 c/kg
 1 rad = 0.01 Gy
 1 rem = 0.01 Sv
 Conversions - SI to Traditional Units
 1 c/kg = 3876 R
 1 Gy = 100 rad
 1 Sv = 100 rem
 1 R ≈ 1 rad ≈ 1 rem
 1 Gy ≈ 1 Sv
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Sources of Ionizing
Radiation
 Natural Sources
•
•
•
Radon gas
Uranium and Thorium in
rock and stone
Galaxy & Sun
 Man-Made Sources
•
•
•
Medical x-rays
Nuclear medicine studies
Consumer products
(e.g., smoke detectors, exit
signs)
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Average Dose Equivalent
~360 mrem/yr
Sources of Radiation Exposure to the US Population
Other
1%
Consumer Products
Other
1%
Nuclear Medicine
4%
3%
Consumer Products
3%
Nuclear Medicine
4%
Medical X-rays
11%
Medical X-rays
11%
Radon
54%
Naturally
Occurring
Radon
54%
Internal
11%
Terrestrial
8%
Cosmic
8%
Cosmic
8%
Internal
11%
Terrestrial
8%
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Dose Comparisons
“Typical” Doses
Flight from Los Angeles to London
Chest X-Ray
Average annual background dose
5 mrem (.05 mSv)
10 mrem (0.1 mSv)
360 mrem (3.6 mSv)
“Comparative” Dose
Skin erythema (reddening)
~300,000 mrad (~3000 mGy)
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Radiation Dose Limits
 Occupational limits
 Effective dose equivalent limit - 5,000 mrem/yr
 Skin, organs, or extremities - 50,000 mrem/yr
 Lens of the eye - 15,000 mrem/yr
 “Declared pregnant woman” - 500 mrem to
embryo/fetus
 Member of the public - 100 mrem/yr
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ALARA
Location
Limit
ALARA I
ALARA II
(mrem/yr)
(mrem/qtr)
(mrem/qtr)
5000
125
375
Lens of the Eye 15,000
375
1125
Extremities/Skin 50,000
1250
3750
Whole body
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Personnel Monitoring
 Two body badges
 One badge should be
worn under all leaded
apparel.
 Second badge should
be worn at the collar
level outside all
leaded apparel.
DO NOT
INTERCHANGE
THESE BADGES
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Personnel Monitoring
 Ring badges should be worn by
operators whose hands are very near the
primary beam
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Minimizing Operator Dose
 ↑ Subject dose ↑ Operator Dose
 ↑ Clarity or detail of image ↑ Operator Dose
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Subject Dose Measurement
Indicators of Dose
 Fluoroscopy time
 DAP (Dose Area Product)
 Cumulative dose at IRP
Limitations
Field sizes
Movement of x-ray tube
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Biological Effects of
Radiation to Operator
Cataract originating in the posterior pole of
the lens of an interventionalist, consistent
with radiation-induced cataract
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Biological Effects of
Radiation to Subject
 Skin injury to animal
 Can range from skin reddening to
tissue necrosis
 May take weeks to months for skin
problems to occur
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Correlation of Dose
Operator and Subject
 With the exception of magnification,
“scatter” radiation dose to operator is
affected by the same parameters as the
radiation dose to the subject
 Low dose to subject = Less scatter = Low
dose to operator
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INCREASE
QUALITY
Lower Dose
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Decrease Radiation Field
Size
 Collimate to the smallest practical field size
 Reduces exposure to subject
 Reduces scatter to operator
 Improves image
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Increase Tube Potential (kVp)
 Lowers scatter since fewer photons will
be needed to penetrate the subject
 In automatic mode, the mA decreases as
the kVp increases
 Therefore, higher kVp generally results in
a lower skin dose to the subject and less
scatter to the operator
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Subject Thickness
 ↑ Thickness ↑ Photons to get to II
 Large subjects and oblique beam angles
may result in significantly higher skin
doses and scatter
 May not be negotiable
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Thickness vs Skin Entrance
Exposure Rate
4.5
4.2
4
Exp. Rate (R/min)
3.5
3
2.74
2.5
Exp. Rate
2
1.5
1.47
1
0.5
0
0
2
4
6
8
Thickness of Subject
10
12
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Use Magnification Sparingly
 Machine automatically reduces the field
size
 Higher “Mag” modes result in higher
doses to smaller areas of the skin
 May negatively affect your research
results
 Instead, reduce field size to the extent
practical when in “normal” mode
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Lower Pulse Rate
 Lower pulse rates result in lower
exposure to the subject and less scatter
to the operator
 Dynamic image quality will be reduced
(image may appear “jerky”)
 Operate in “pulse rate” mode whenever
possible
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Exposure Rate
Affected by Magnification and Pulse Rate
7
6.24
6
Exp. Rate (R/min)
5.23
5
4
4
3.15
2.68
3
Normal (9")
Mag1 (7")
2.09
Mag2 (5")
2
1
0
7.5
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Pulse Rate (Pulses/sec)
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Minimize High Dose Rate
Mode (Cine)
 A high dose rate mode (“cine”) is used to
capture digital images
 20 times the dose rate from standard
fluoroscopy
 A minimum number of these runs should
be used consistent with obtaining
adequate information
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Subject Distances to
Tube and II
 Maximize distance between tube &
subject
 Minimize distance between subject and II
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“Danger” Zone between
X-ray Tube and Subject
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“Danger Zone” Analogy
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Reducing Exposures
“TDS”
 Time
 Distance
 Shielding
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Reducing Exposures
Time
 Minimize fluoro time to reduce subject
dose and scatter dose to operator
 Use “image hold” capabilities to reduce
need for additional fluoro time
 Personnel should not be in the room
unless their presence is necessary to the
procedure.
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Reducing Exposures
Distance
 Radiation follows the “inverse square law”
2 R/min
8 R/min
32 R/min
2 meters
1 meter
½ meter
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Reducing Exposures
Shielding
 Pb aprons (at least 0.5
mm Pb equivalent)
should be worn by all
personnel involved in
fluoro/cine procedures
 Thyroid collars and Pb
glasses may also be
recommended or
required
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Reducing Exposures
Shielding
 Portable/pulldown shields
may be utilized
 Pb drapes on
table and image
intensifier
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Dose Reduction Summary
 Use pulsed fluoroscopy or other low-doserate modes of operation
 Keep tube current low and tube potential
high
 Optimum kVp – below gives better contrast
at expense of dose increase and above
decreases subject dose and image quality
 Use heavy beam filtration to increase kVp
 Use “image hold” to avoid repetitive
exposure
 Use magnification modes sparingly
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Dose Reduction Summary
 Do not remove devices designed to maintain
adequate distance between x-ray tube &
subject (beam separator device)
 Collimate to the smallest reasonable field size
 Utilize dose monitoring equipment (e.g.,
radiation badge)
 Keep x-ray tube as far from subject as possible
and image intensifier as close to subject as
possible
 Avoid prolonged exposures over the same skin
area, especially through thick body masses
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Radiation Safety Office
Clinical Building – Room 159
274-4797
After hours pager 312-1519
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