Transcript Radiation Safety in the PET Facility

Radiation Safety
Considerations for PET/CT
Robert E. Reiman, MD, ABNM
Radiation Safety / OESO
Duke University Medical Center
Radiation Safety? Who
Cares!
Why We Have Radiation
Protection Programs
• December 1895: Roentgen discovers
x-rays.
• 1/1896 – 12/1896: 23 cases of
radiation dermatitis documented.
• 1911 –1914: 252 radiation-induced
cancer cases with 54 fatalities.
“I’m From the
Government, and I’m
Here to Help You...”
Why We’re Regulated
In the early years of the
Twentieth Century, radium was
widely promoted as a cure for
practically everything, from
cancer to baldness. Radium
was added to hundreds of
“over-the-counter” commercial
“beauty” and “health”
products.
Why We’re Regulated
Eben Byers, socialite and
U.S. Open champion, drank
three bottles of “Radithor” a
day for three years. He died
a painful death from
radionecrosis of the jaw and
skull in 1932. After a
Congressional inquiry, the
FDA seized oversight of
radium-containing products.
PET/CT Regulations
• “10 CFR 20” – Title 10 (Energy), Code of
Federal Regulations, Part 20
• “10 CFR 35” – Title 10, Code of Federal
Regulations, Part 35
• 10 CFR 20 addresses general standards
for radiation protection.
• 10 CFR 35 addresses use of “by-product”
materials in medicine.
PET/CT Regulators
• NRC directly oversees 17 states.
• 33 “Agreement States” implement NRC
regulations...and then some.
• FDA regulates production of PET
radiopharmaceuticals, and manufacture and
sale of CT scanners.
• Individual states regulate operation of CT
scanners.
Helpful Organizations
• International Commission on
Radiological Protection (ICRP)
• National Council on Radiation Protection
and Measurements (NCRP)
• Nuclear Regulatory Commission (NRC)
• “Agreement State” Radiation Protection
Agencies
Principle of “ALARA”
As
Low
As
Reasonably
Achievable
Annual Radiation Dose Limits
Population
Rad. Workers
NCRP 91
10 CFR 20
5 /15/50 rem
5/15/50 rem
1 x age lifetime
No Lifetime
Occasion.
Exposed
0.5/5/5 rem
0.5 rem
Gen. Public
0.5/5/5 rem
0.1 rem
Minor
Trainees
0.1 rem
0.5 rem
Fetus
0.5 rem
0.5 rem
50 mrem / month
No monthly
Radiation Warning Signs
Cyclotron
“Hot” Lab
PET/CT Scanner
Record Retention
• Shipping and Receiving (3 years)
• Area Surveys and Trash Surveys (3 years)
• Public Dose Limit Compliance (3 years)
• Personnel Dosimetry (lifetime)
Criteria for Personnel
Monitoring
• 10 CFR 20: Personnel monitoring
occupational dose is required if the sum
of external and internal EDE could be
expected to exceed 10 % of the annual
whole-body occupational limit.
• Licensees can monitor at lower exposure
levels as part of an ALARA program.
Survey Meter Quality
Assurance
• Meters OFF when not in use
• Operation check with each use
• Regular battery and high-voltage checks
• Annual calibration
Hands in the Beam?
• NO hands in the useful
(primary) beam unless
protected by 0.5 mm
lead or equivalent
shielding.
• Mechanical patient
restraint should be
used whenever
practical in lieu of
human holders.
Health Physics, Aug 2003
Medical Events:
Administrative Criteria
• Administered to wrong patient or research
subject.
• Wrong radiopharmaceutical administered.
• Wrong route of administration.
• Administered activity differs from that in
the written directive by more than 20
percent.
Medical Events: Dose
Criteria
• Effective Dose Equivalent > 5 rem (0.05 Sv).
• Single organ / tissue dose > 50 rem (0.5 Sv).
Reporting Medical Events
• Must notify NRC / Agreement State agency
within one calendar day after discovery.
• Must follow up with a written report within 15
days after discovery.
• Must notify referring physician within 24 hours.
• Must notify patient or guardian unless
contraindicated by referring physician.
I Already Know All This
Stuff...Why Is PET/CT
Different?
PET = Nuclear Medicine on Steroids
PET
+
=
CT
TWICE the
Headaches
Why is PET Different?
• PET radionuclides have higher Exposure
Rate Constants than “traditional” nuclear
medicine radionuclides.
• Photon energies are higher.
• Half-lives are shorter.
Higher Exposure Rate Constants
Radionuclide
Fluorine-18
ERC (R/hr/mCi at 1
cm from point source)
6.0
Indium-111
3.4
Gallium-67
1.1
Technetium-99m
0.6
Thallium-201
0.4
Higher Dose Rate From Patients
Radionuclide
Fluorine-18
Admin. Act.
Dose Rate
(mCi)
(mrem/hr at 1 m)
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
PET Shielding: Tenth Value Layers
Radionuclide
TVL* (mm) for Lead
Fluorine-18
13.7
Gallium-67
4.7
Indium-111
2.2
Technetium-99m
0.9
Thallium-201
0.9
* TVL = thickness of material required to absorb 90% of photons
Shorter Physical 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 >> Lower Dose*
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
*Dose received by a bystander at 1 meter during 5 half-lives or more
How Can I Minimize
My Staff’s Exposure?
PET/CT: Sources of
Exposure to Staff
•
•
•
•
•
•
Cyclotron (?)
Radiopharmaceutical Production (?)
Dose Dispensing / Calibration
Dose Administration
Patients
X-rays From CT
What Doses Do People Get?
Study
NM-Tech
(rad/scan)
CT-Tech
Patient
(rad/scan) (rem/scan)
Standard
PET
Finger: 0.12
Breast: 0.03
---
0.70
PET/CT
Finger: 0.20
Breast: 0.02
Finger: 0.04
Breast: 0.03
2.5
Ref: Beyer T, Mueller SP, Brix G et al. Radiation exposure during
combined whole-body FGD-PET/CT imaging. 51st Annual Meeting,
Society of Nuclear Medicine, June 22, 2004. Abstract 1331.
Measures to Reduce
Personnel Dose
• Time, Distance and Shielding
• Laboratory Technique
• Administrative and Procedural Controls
Good Hot Lab Technique
•Cover work surfaces
•Protective gloves
•Wash hands frequently
Things NOT To Do in the Hot Lab
•Don’t Drink
•Don’t Eat
•Don’t Smoke
•No cosmetics
Minimize Time and Maximize Distance!
Technologists should minimize the time spent in close
proximity (less than two meters) from the patient.
Maximize Distance!
• Inverse Square Law ( 1/r2 )
• Dramatic reductions in exposure
• Simulations of PET technologist’s
interactions with patients show that 75%
of dose is accumulated during time tech
is within 2 meters of patient.
I Got 8 mrem!
I’m Outta
Here...
I Got 2 mrem!
I Got 0.1 mrem!
I Got 0.5 mrem!
Utilize 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).
PET Barrier Materials
Material
Tungsten
Tenth-Value Layer
(cm at 511 keV)
0.89
Lead
1.37
Lead glass
2.65
Concrete
11.3
Typical Hot Lab “Shadow” Shield
Other Shielding Methods
Unit Dose Stations
Syringe Shields (Tungsten
and Lead Glass)
Shielding: If you can’t be in
the shielded booth...
...then stand behind the doc.
X-Ray Protective Equipment
X-ray Aprons -- No Protection at
511 KeV
The “lead” aprons used in
diagnostic radiology have
about 0.5 mm lead equivalent.
These afford significant
protection at energies under
120 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
How Do I Minimize Radiation
Exposure to My Patients?
Reducing PET/CT
Patient Dose
•
•
•
•
Optimize administered radioactivity.
Reduce CT mAs.
Increase “pitch”.
Technique charts to minimize CT
exposure to pediatric patients and small
adults.
Reducing PET/CT Patient Dose
Protocol
Range
kVp
mAs
Dose
(rem)
Standard
Whole Body
130
111
2.4
RangeAdapted
Abdomen
130
147
Low-Dose
2.5
Chest
130
80
Whole Body
130
15
0.8
Ref: Beyer T, Mueller SP, Brix G et al. Radiation exposure during combined wholebody FGD-PET/CT imaging. 51st Annual Meeting, Society of Nuclear Medicine, June
22, 2004. Abstract 1331.
Avoiding “Medical Events”
• Use Texas as an example (detailed
information accessible).
• Look at the “Root Causes” of
radiopharmaceutical errors.
• Look at corrective actions taken.
Source: Texas Department of Health
Corrective Actions
• Increasing staff awareness and
retraining.
• Addition of policies or procedures.
• Modification of existing policies and
procedures.
• Addition of engineering controls.
• Termination of staff.
Source: Texas Department of Health
How Do I Minimize Radiation
Exposure to Families and the
General Public?
Regulatory Requirements
• Written Instructions on minimizing exposure to
others must be provided to patient if a member
of the public could receive over 100 millirem.
• Patient may be released if “public dose” is less
than 500 millirem.
• Reference: NRC Regulatory Guide 8.39
“Patient Release” Guidelines
Radionuclide Admin. Activity Below
Which Patient Can be
Released*
Admin. Activity Above
Which Instructions
must be Provided*
F-18
253 mCi
51 mCi
C-11
1,400 mCi
281 mCi
N-13
2,800 mCi
558 mCi
*Calculated per USNRC Regulatory Guide 8.39,
assuming occupancy factor of 0.75 at one meter
Annual Dose Limit to NonRadiation Workers
• Member of the “general public” is
limited to 100 millirem per year.
• Non-PET staff in adjacent areas are the
same as the “general public”.
• “General Public” will be the limiting
consideration in shielding design.
Principles of PET/CT
Shielding Calculations
• Identify the potentially exposed population and
determine a limiting weekly dose.
• Characterize the x-ray equipment / PET doses.
• Characterize the site.
• Determine “Use” and “Occupancy” factors.
• Choose a barrier material.
• Calculate barrier thickness and location.
D1 = dose due to one patient at one meter from scanner
Do = dose due to one patient at point of occupancy
Occupied Area
(< 100 mrem/yr)
Scanner Room
Patient
D1
(Photon Flux)
1m
Do
d
Barrier
Do = D1 / d2
E = ( Ē x W x U x T ) / d2
X-ray Tube
(W, Ē)
(Primary Beam)
Up
T
T
d
Us (= 1)
Give Up and Hire a
Consultant.
How Do I Avoid Radiation
Exposure to the Fetus?
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
Ref: Russell J, Sparks R, Stabin M, Toohey R. Radiation Dose
Information Center, Oak Ridge Associated Universities.
If One of Your Staff
Becomes Pregnant...
• Confidential “Declaration of
Pregnancy”.
• Information regarding fetal effects.
• Fetal dose monitoring during
pregnancy.
Internet Resources
• U.S. Nuclear Regulatory Commission:
www.nrc.gov
• FDA: www.fda.gov/cdrh/index.html
• Radiation Internal Dose Information Center:
www.orau.gov/reacts/compendia.htm (Dose
from internally-deposited radionuclides)
Internet Resources
• Center for Disease Control:
www.cdc.gov/other.htm (Web addresses of
State Health Departments)
• Health Physics Society: www.hps.org