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”

AsLowAsReasonablyAchievable

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

Radiation Warning Signs

Cyclotron PET/CT Scanner“Hot” Lab

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

+ =

TWICE the Headaches

PET

CT

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 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

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

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)

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

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

(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.

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 Got 2 mrem!

I Got 0.5 mrem!

I Got 0.1 mrem!

I’m Outta Here...

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 Tenth-Value Layer (cm at 511 keV)

Tungsten 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....then stand behind the doc.

X-Ray Protective Equipment

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.

Measures to Reduce Dose: Other Techniques

Mobile Shields Syringe Shields (Tungsten and Lead Glass)

Tongs to Maximize Distance

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

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.

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 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.

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.

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

d

X-ray Tube(W, Ē)

Up

Us (= 1)

TT

E = ( Ē x W x U x T ) / d2

(Primary Beam)

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