Nuclear Medicine Physics Jerry Allison, Ph.D. Department of Radiology Medical College of Georgia...

Nuclear Medicine Physics

Jerry Allison, Ph.D.

Department of Radiology

Medical College of Georgia

Radioiodine Therapy

A note of thanks to

Z. J. Cao, Ph.D.

Medical College of Georgia

And

Sameer Tipnis, Ph.D.

G. Donald Frey, Ph.D.

Medical University of South Carolina

for

Sharing nuclear medicine presentation content

http://www.hpschapters.org/northcarolina/fall2008/TPM.3.pdf

Thyroid Uptake/Imaging

• I-123: 100 – 200 mCi (g only) T1/2 = 13.2 h

• 1-131: 15 – 100 mCi (g & b) T1/2 = 8 d

Thyroid probe

Measure thyroid uptake of I-131 in-vivo

5×5 cm NaI(Tl) with 15 cm long conical collimator

pointing to neck and thigh (bkg)

calibration phantom with known activity for calculating

uptake (pt capsule)

1 – 2 cm difference in depth 10 – 40% difference in count rate

Thyroid uptake neck phantom

For use with thyroid uptake probe.

Used to estimate atteuation and scatter for soft tissue overlying thyroid glad.

Approximates typical patient neck geometry.

http://www.biodex.com/nuclear-medicine/products/thyroid-uptake-system/thyroid-uptake-system-accessories/thyroid-uptake-nec

Thyroid

http://www.hpschapters.org/northcarolina/fall2008/TPM.3.pdf

- Emitters

• - (beta) - 131I, 90Y, 153Sm

2015 Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

b- decay

• A neutron decays to a proton, electron and anti- neutrino: n p + e- +.

• e- and created inside the nucleus at the moment of decay and ejected instantaneously

• AXz AYz+1 • e.g. 131I53 131Xe54 + e- +

e-

Applications

• - emitters – used for therapy - cannot escape pt, localized energy deposition 90Y (pure -) 131I , 153Sm (- and )


131I Production

• Reactor produced as fission product

131I Decay

© Physics in Nuclear Medicine: Cherry, Sorenson and Phelps

131I Decay

https://en.wikipedia.org/wiki/File:Iodine-131-decay-scheme-simplified.svg

I-131 Absorbed Dose

http://www.nuclearonline.org/PIbyGeneric2.htm

90% of pt dose is b; 10% by g

Written directive• Required for I-131 dose exceeding 30

μCi

• Pregnancy test results

• Order for the radiopharmaceutical is written twice Once to order the drug The second dosage usually represents the

actual amount given Route of administration

• Must be signed by an authorized user

NM Written Directive for I-131 Therapy

http://www.gru.edu/services/ehs/radsafe/

Authorized User

• A physician licensed to practice and who meets specific requirements (NRC) and identified as an AU on the institution’s license or permit Board Certified (by appropriate Board)

• Other physicians and technologists may work with byproduct material under the supervision of an AU

• All radiopharmaceuticals dispensed or administered must be pursuant to an order (e.g. prescription) of an AU


• Authorized User

10CFR35.290 Training for imaging and localization studies Has completed 700 hours of training and experience, including a minimum of 80 hours of classroom and laboratory training http://www.nrc.gov/reading-rm/doc-collections/cfr/part035/part035-0290.html

• Authorized User 10CFR35.390 Training for use of unsealed byproduct material for which a written directive is required Has completed 700 hours of training and experience, including a minimum of 200 hours of classroom and laboratory training

http://www.nrc.gov/reading-rm/doc-collections/cfr/part035/part035-0390.html

• Authorized User

10CFR35.392 Training for the oral administration of sodium iodide I-131 requiring a written directive in quantities less than or equal to 1.22 gigabecquerels (33 millicuries) Administering dosages to patients …, that includes at least 3 cases involving the oral administration of less than or equal to 1.22 gigabecquerels (33 millicuries) of sodium iodide I-131


• Authorized User

35.394 Training for the oral administration of sodium iodide I-131 requiring a written directive in quantities greater than 1.22 gigabecquerels (33 millicuries) Administering dosages to patients …, that includes at least 3 cases involving the oral administration of greater than 1.22 gigabecquerels (33 millicuries) of sodium iodide I-131


131I studiesFor 131I doses > 30 µCi a “written directive” which may only be issued by an AU is required for each treatment

Radiology residents (under AU supervision) need to direct 3 treatments < 33 mCi and 3 > 33 mCi to be “AU Eligible”


Getting “AU Eligible”Radiology Residents who • Complete the requirements during their

residency• Get “OK” from the residency director• Pass the RISE exam (part of core exam)

Radioisotope Safety Exam (~60 items)• ~15 NM physics items• ~15 NM safety items• ~20 NM clinical items• ~20 NM regulatory/administrative items


COMPLIANCE WITH NRC TRAINING AND EXPERIENCE REQUIREMENTS

26

Release of I-131 therapy patients

• I-131 in patients may be excreted in their urine, perspiration and saliva and these body fluids can contaminate household surfaces.

• Use separate bathroom• Shower/brush teeth frequently• Limit hugs, sleep alone• Limit visitors and co-workers• Limited length of stay time

27

Release of I-131 therapy patients

• Avoid public transportation• Children, pregnant women and nursing mothers

must stay at least 6’ away.• Written instructions must be provided to the

patient to minimize radiation exposure to public if a member of the public could receive a dose greater than 1 mSv.

Radioiodine Safety Manuals at MCG


Radioiodine Procedures and Nursing Instructions


Signage• Radioactive Material• Entry Log• Instructions• No Housekeeping

Shoe covers, absorbent floor pads

Plastic sheeting, absorbent floor pad, furniture covers

Disposable trash container (hazardous)

Bed rails covered

Toilet cover

Sink cover

Vanity cover

Absorbent sink cover

Door handle covers

Release of I-131 therapy patients• A patient may be released if the total

effective dose to any other individual (family or caregiver) is not likely to > 5 mSv

• Patients receiving diagnostic nuclear medicine examinations can be released without any calculations

• 131I Therapy patients need special instructions


Radiation exposure rate around patient

Typical exposure rate at 1 m from the patient soon after injection:

• Most diagnostic radiopharmaceuticals: <1 mR/hr (maximum dose to public 1 mSv/yr)

• 18F-FDG: ~5 - ~30 mR/hr

• 131I: ~5 or ~30 mR/hr for Graves or cancer dose respectively

Breast feeding Guidelines (recommended / not regulated)

Radiopharmaceutical Recommendation

131I NaI Cessation

123I NaI Cessation

67Ga Citrate Cessation

201Tl Chloride 96 hrs

123I MIBG, 99mTc WBC 48 hrs

99mTc MAA, 99mTc RBC 12 hrs


Lactating 131I therapy pts

• Lactating breasts accumulate radioiodine Patient breast dose can be quite high Breast pump reduces breast dose

• Lactating completely ceases 4 wks post-partum with no breast feeding

• Ask pt to stop breastfeeding 15 days BEFORE therapy


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Absorbed dose to fetus

99mTc MAA 0.35 (mSv/mCi)99mTc sulfur colloid 0.3599mTc RBC 0.6099mTc DTPA 0.3599mTc diphosphonate 0.4067Ga citrate 2.50111In leukocytest 4.00131I (15% uptake) 1.00123I (15% uptake) 0.35201Tl chloride 3.00133Xe 0.01

Fetal thyroid dose from 131I• 131I can rapidly cross the placenta• Fetal thyroid starts concentrating 131I

after 11 to 12th week post-conception• Ability rapidly increases after 22nd week• Can result in hypothyroidism / ablation• Critical to check pt for pregnancy before

131I therapy


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Homeland security

• Extremely sensitive radiation detectors aredeployed in train stations, airports, tunnels, etc.

• I-131 patients may set off alarms up to 95 days following a therapy procedure.

• Give a letter containing radionuclide and hospital contact information.

What is major spill?

• Activity released at location or on people 100 mCi Tc-99m or Tl-201 10 mCi Ga-67 or In-111 1 mCi I-131

• Radiation safety officer must be present.

• Focus on containment, shielding, and decontaminating individuals

Nuclear Medicine Physics Jerry Allison, Ph.D. Department of Radiology Medical College of Georgia...

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