Transcript Radiation Safety in the PET Facility

Academy of Molecular Imaging
PET Radiation Safety
Robert E. Reiman, MD, ABNM
Radiation Safety / OESO
Duke University Medical Center
Topics to Consider
• General Regulatory / Practice Considerations
• Why is PET Different?
• External Radiation Hazards
• Measures to Reduce Personnel Dose
General Requirements:
Annual Dose Limits
• Total effective dose equivalent to whole
body: 5 rem
• Lens of eye: 15 rem
• Sum of deep-dose and committed dose
equivalents to all other tissues and
extremities: 50 rem
• Fetus: 0.5 rem
General Requirements: Records
• Shipping and Receiving
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Personnel Dosimetry
Area Surveys
Trash Surveys
Public Dose Limit Compliance
General Requirements:
Radiation Signs
> 500 rem/hr
> 100 mrem/hr
Hot Lab,
Scanner Areas
General Requirements:
Personal Dosimeters
Wear with the label on
the palmar (inside)
surface of the hand
Wear at the chest
or waist
General Requirements:
Survey Instruments
General Requirements:
Survey Meter QA
• Meters OFF when not in use
• Operation check with each use
• Regular battery and high-voltage checks
• Annual calibration
Good Hot Lab Procedures
•Cover work surfaces
•Use correct pipetting technique
•Wash hands frequently
Things NOT To Do in the Lab
•Don’t Drink
•Don’t Eat
•Don’t Smoke
•No cosmetics
Why is PET Different?
• PET radionuclides have higher Exposure Rate
Constants than “traditional” nuclear medicine
radionuclides.
• Photon energies are higher.
• Half-lives are shorter.
Why PET is Different:
Exposure Rate Constants
• The “Exposure Rate Constant” of a
radionuclide is the exposure rate (roentgens
per hour) measured at one centimeter from a
source with activity of one millicurie.
• For positron emitters, ERC is about 6 R/hr per
millicurie at one centimeter.
Higher Exposure Rate Constants
Radionuclide
ERC (R/hr/mCi at 1 cm)
Fluorine-18
6.0
Indium-111
3.4
Gallium-67
1.1
Technetium-99m
0.6
Thallium-201
0.4
Higher Exposure Rate Constants
Radionuclide
Admin. Act.
(mCi)
Exp. Rate
(mR/hr at 1 m)
Fluorine-18
12.0
4.0
Technetium-99m
30.0
0.6
Gallium-67
10.0
0.4
Indium-111
0.5
0.06
Thallium-201
4.0
0.05
Why PET is Different:
Photon Energy
• Photon energy is 0.511 MeV for positron
emitters.
• This higher photon energy is more difficult to
shield (using lead) than “traditional” nuclear
medicine radionuclides.
Higher Photon Energy
Radionuclide
TVL (mm)
Fluorine-18
13.7
Gallium-67
4.7
Indium-111
2.2
Technetium-99m
0.9
Thallium-201
0.9
Why PET is Different:
Half-Life
• The half-lives of radionuclides used in
PET imaging are much shorter (minuteshours) than those of “traditional”
radionuclides (hours-days).
• This leads to cumulated doses that are
lower than you might expect, given the
very high ERC.
Shorter Half-Life
Radionuclide
Half-Life
Gallium-67
3.26 days
Thallium-201
3.04 days
Indium-111
2.83 days
Technetium-99m
6.02 hours
Fluorine-18
109.8 minutes
Shorter Half-Life
Radionuclide
Admin.
Activity (mCi)
Gallium-67
10.0
Cum. Dose at
1 m (mrem)
26.6
Fluorine-18
12.0
5.5
Indium-111
0.5
3.9
Technetium-99m
30.0
3.3
Thallium-201
4.0
2.9
FDG PET: Sources of External
Radiation to Staff
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Cyclotron
Fluoride Transport
FDG Production
Dose Dispensing / Calibration
Dose Administration
Patients
Types of External Exposure
• Positrons: Non-penetrating. Most are
stopped in glassware, syringes, patient;
etc. However, energetic positrons have
formidable ranges in air.
• Annihilation Photons: Penetrating.
Energy = 511 KeV. “Tenth-value Layer” in
lead is 1.37 cm.
Measures to Reduce
Personnel Dose
• Time, Distance and Shielding
• Laboratory Technique
• Administrative and Procedural Controls
Measures to Reduce Dose:
Minimize Time!
• Total radiation dose is the product of dose
rate and duration of exposure.
• For a given exposure rate, less time
means less dose.
• So – perform tasks quickly but safely.
• Try not to spend unnecessary time around
the patient.
Measures to Reduce Dose:
Maximize Distance!
Technologists should minimize the time spent in close
proximity (less than two meters) from the patient.
4 meters
2
1
0.5
15
4
1.0
0.3 mrem/hr
Measures to Reduce Dose:
Shielding
Positrons can be stopped by 2 - 5 mm Lucite. Gammas require a
high-Z material. Neutrons require high hydrogen content (paraffin
or the “waters of hydration” in concrete).
Typical “Shadow” Shield
“Rule of Thumb: Shadow Shield provides maximum
reduction of about 1 part in 400
X-ray Aprons -- No Protection
at 511 KeV
The “lead” aprons used in
diagnostic radiology have about
0.5 mm lead equivalent. These are
protective at energies under 100
KeV, but are nearly useless
against annihilation photons.
100 KeV: Transmission = 4.3 %
511 KeV: Transmission = 91.0 %
Measures to Reduce Dose:
Other Techniques
Tongs to Maximize
Distance
Mobile Shields
Syringe Shields (Tungsten
and Lead Glass)
Measures to Reduce Dose:
Procedural Controls
• Automated dose dispensing and
Calibration (“Unit” Dose)
• Elimination or automation of “flush”
during patient administration
• Rotation of personnel
Prevention of Unintentional
Fetal Exposure
• Good History (includes asking direct
question “Are you pregnant?”)
• Common-sense Assessment of Risk of
Pregnancy (age, surgical hx, contraception)
• Beta HCG
• Cannot prevent all unintentional exposures.
Fetal Doses (rads)
mCi
Early
3 Mo.
6 Mo.
9 Mo.
FDG
10
1.0
0.63
0.35
0.30
MDP
30
0.68
0.60
0.30
0.27
Nuclear Medicine procedure doses courtesy: Russell J, Sparks R, Stabin
M, Toohey R. Radiation Dose Information Center, Oak Ridge Associated
Universities.
In Summary...
• PET personnel exposures have the potential
to be higher than in “standard” settings.
• Doses can be minimized by
time/distance/shielding measures.
• Special administrative and engineering
measures can further reduce dose.