Radiation Safety Considerations for PET/CT Robert E. Reiman, MD, ABNM Radiation Safety / OESO Duke...
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Transcript of Radiation Safety Considerations for PET/CT Robert E. Reiman, MD, ABNM Radiation Safety / OESO Duke...
![Page 1: Radiation Safety Considerations for PET/CT Robert E. Reiman, MD, ABNM Radiation Safety / OESO Duke University Medical Center.](https://reader030.fdocuments.us/reader030/viewer/2022032313/56649e715503460f94b6f8f1/html5/thumbnails/1.jpg)
Radiation Safety Considerations for PET/CT
Robert E. Reiman, MD, ABNM
Radiation Safety / OESO
Duke University Medical Center
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Radiation Safety? Who Cares!
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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.
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“I’m From the Government, and I’m Here to Help You...”
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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.
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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.
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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.
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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.
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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
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Principle of “ALARA”
AsLowAsReasonablyAchievable
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Annual Radiation Dose Limits
Population NCRP 91 10 CFR 20
Rad. Workers 5 /15/50 rem1 x age lifetime
5/15/50 remNo 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 rem50 mrem / month
0.5 remNo monthly
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Radiation Warning Signs
Cyclotron PET/CT Scanner“Hot” Lab
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Record Retention
• Shipping and Receiving (3 years)
• Area Surveys and Trash Surveys (3 years)
• Public Dose Limit Compliance (3 years)
• Personnel Dosimetry (lifetime)
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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.
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Survey Meter Quality Assurance
• Meters OFF when not in use
• Operation check with each use
• Regular battery and high-voltage checks
• Annual calibration
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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
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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.
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Medical Events: Dose Criteria
• Effective Dose Equivalent > 5 rem (0.05 Sv).
• Single organ / tissue dose > 50 rem (0.5 Sv).
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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.
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I Already Know All This Stuff...Why Is PET/CT
Different?
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PET = Nuclear Medicine on Steroids
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+ =
TWICE the Headaches
PET
CT
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Why is PET Different?
• PET radionuclides have higher Exposure Rate Constants than “traditional” nuclear medicine radionuclides.
• Photon energies are higher.
• Half-lives are shorter.
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Higher Exposure Rate Constants
Radionuclide ERC (R/hr/mCi at 1 cm from point source)
Fluorine-18 6.0
Indium-111 3.4
Gallium-67 1.1
Technetium-99m 0.6
Thallium-201 0.4
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Higher Dose Rate From Patients
Radionuclide Admin. Act. (mCi)
Dose Rate
(mrem/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
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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
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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
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Shorter Half-Life >> Lower Dose*
Radionuclide Admin. Activity (mCi)
Cum. Dose at
1 m (mrem)
Gallium-67 10.0 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
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How Can I Minimize My Staff’s Exposure?
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PET/CT: Sources of Exposure to Staff
• Cyclotron (?)
• Radiopharmaceutical Production (?)
• Dose Dispensing / Calibration
• Dose Administration
• Patients
• X-rays From CT
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What Doses Do People Get?
Study NM-Tech
(rad/scan)
CT-Tech
(rad/scan)
Patient
(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.
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Measures to Reduce Personnel Dose
• Time, Distance and Shielding
• Laboratory Technique
• Administrative and Procedural Controls
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Good Hot Lab Technique
•Cover work surfaces•Protective gloves•Wash hands frequently
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Things NOT To Do in the Hot Lab
•Don’t Drink•Don’t Eat•Don’t Smoke•No cosmetics
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Minimize Time and Maximize Distance!
Technologists should minimize the time spent in close proximity (less than two meters) from the patient.
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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.
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I Got 8 mrem!
I Got 2 mrem!
I Got 0.5 mrem!
I Got 0.1 mrem!
I’m Outta Here...
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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).
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PET Barrier Materials
Material Tenth-Value Layer (cm at 511 keV)
Tungsten 0.89
Lead 1.37
Lead glass 2.65
Concrete 11.3
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Typical Hot Lab “Shadow” Shield
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Other Shielding Methods
Unit Dose Stations Syringe Shields (Tungsten and Lead Glass)
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Shielding: If you can’t be in the shielded booth...
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...then stand behind the doc....then stand behind the doc.
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X-Ray Protective Equipment
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X-ray Aprons -- No Protection at 511 KeV
100 KeV: Transmission = 4.3 %
511 KeV: Transmission = 91.0 %
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.
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Measures to Reduce Dose: Other Techniques
Mobile Shields Syringe Shields (Tungsten and Lead Glass)
Tongs to Maximize Distance
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Measures to Reduce Dose: Procedural Controls
• Automated dose dispensing and Calibration (“Unit” Dose)
• Elimination or automation of “flush” during patient administration
• Rotation of personnel
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How Do I Minimize Radiation Exposure to My Patients?
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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.
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Reducing PET/CT Patient Dose
Protocol Range kVp mAs Dose
(rem)Standard Whole Body 130 111 2.4
Range-Adapted
Abdomen 130 147
2.5Chest 130 80
Low-Dose Whole Body 130 15 0.8
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.
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Avoiding “Medical Events”
• Use Texas as an example (detailed information accessible).
• Look at the “Root Causes” of radiopharmaceutical errors.
• Look at corrective actions taken.
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Source: Texas Department of Health
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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.
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Source: Texas Department of Health
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How Do I Minimize Radiation Exposure to Families and the
General Public?
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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
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“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
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Annual Dose Limit to Non-Radiation 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.
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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.
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d
Patient
(Photon Flux)
Scanner Room Occupied Area(< 100 mrem/yr)
Barrier
1 m
D1
Do
Do = D1 / d2
D1 = dose due to one patient at one meter from scannerDo = dose due to one patient at point of occupancy
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d
X-ray Tube(W, Ē)
Up
Us (= 1)
TT
E = ( Ē x W x U x T ) / d2
(Primary Beam)
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Give Up and Hire a Consultant.
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How Do I Avoid Radiation Exposure to the Fetus?
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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.
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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.
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If One of Your Staff Becomes Pregnant...
• Confidential “Declaration of Pregnancy”.
• Information regarding fetal effects.
• Fetal dose monitoring during pregnancy.
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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)
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Internet Resources
• Center for Disease Control: www.cdc.gov/other.htm (Web addresses of State Health Departments)
• Health Physics Society: www.hps.org