1. Nuclear Medicine Physics
Radioiodine Therapy
Jerry Allison, Ph.D.
Department of Radiology & Imaging
Medical College of Georgia
Augusta University

2. Medical College of Georgia And Sameer Tipnis, Ph.D.
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

5. Thyroid Uptake/Imaging
I-123: 100 – 200 mCi (g only)
T1/2 = 13.2 h
g energies: 159 keV, …
1-131: 15 – 100 mCi (g & b)
T1/2 = 8 d
g energies: 364 keV, …

6. 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

7. Thyroid uptake neck phantom
For use with thyroid uptake probe.
Used to estimate attenuation and scatter for soft tissue overlying thyroid glad.
Approximates typical patient neck geometry.

8. Thyroid

9. - Emitters - (beta) - 131I, 90Y, 153Sm
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

10. 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- 

11. Applications - emitters – used for therapy
- cannot escape pt, localized energy deposition
90Y (pure -)
131I , 153Sm (- and )
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

12. 131I Production
Reactor produced as fission product

13. 131I Decay
© Physics in Nuclear Medicine: Cherry, Sorenson and Phelps

14. 131I Decay

15. I-131 Absorbed Dose 90% of pt dose is b; 10% by g

16. Definitions
Absorbed dose D (Gy): energy deposited in a unit mass of absorber
1 Gy = 1 joule/kg (SI unit)
1 rad = 100 erg/g (traditional unit)
1 Gy = 100 rad

17. Written directive Required for I-131 activity exceeding 30 μCi
Pregnancy test results
Radiopharmaceutical/dosage is entered 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

18. NM Written Directive for I-131 Therapy

19. 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
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

20. Authorized User 10CFR 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

21. Authorized User 10CFR 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

22. Authorized User 10CFR 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

23. Authorized User 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

24. 131I studies
For 131I activities > 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”
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

25. 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
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

26. COMPLIANCE WITH NRC TRAINING AND EXPERIENCE REQUIREMENTS

27. 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

28. 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 total effective dose greater than 1 mSv.

29. Definitions
Effective dose E (Sv): measure of absorbed dose to whole body, the product of equivalent dose and organ specific weighting factors
Whole body dose equivalent to the nonuniform dose delivered

30. Radioiodine Safety Manuals at MCG
Nuclear Medicine
Radiation Oncology

31. Radioiodine Procedures and Nursing Instructions (from Rad
Radioiodine Procedures and Nursing Instructions (from Rad. Safety Manual)

32. Signage
Radioactive Material
Entry Log
Instructions
No Housekeeping

33. Shoe covers, absorbent floor pads

34. Plastic sheeting, absorbent floor pad, furniture covers

35. Disposable trash container (hazardous)

36. Bed rails covered

37. Toilet cover

38. Sink cover

39. Vanity cover

40. Absorbent sink cover

41. Door handle covers

42. 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
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

43. Radiation exposure rate around patient
Typical exposure rate at 1 m from the patient soon after injection:
Most diagnostic radiopharmaceuticals:
<1 mR/hr (maximum total effective dose to public 1
mSv/yr)
18F-FDG: ~5 - ~30 mR/hr
131I: ~5 or ~30 mR/hr for Graves or cancer respectively

44. Breast Feeding Cessation Guidelines (recommended / not regulated)
Radiopharmaceutical
Recommendation
131I NaI
Cessation
123I NaI
67Ga Citrate
201Tl Chloride
96 hrs
123I MIBG, 99mTc WBC
48 hrs
99mTc MAA, 99mTc RBC
12 hrs
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

45. 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
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

46. Absorbed dose to fetus 99mTc MAA 0.35 (mSv/mCi)
99mTc sulfur colloid 0.35
99mTc RBC
99mTc DTPA
99mTc diphosphonate 0.40
67Ga citrate
111In leukocytes 4.00
131I (15% uptake) 1.00
123I (15% uptake) 0.35
201Tl chloride
133Xe

47. Fetal thyroid dose from 131I
131I can rapidly cross the placenta
Fetal thyroid starts concentrating 131I after about the12th week post-conception
Ability rapidly increases after 22nd week
Can result in hypothyroidism / ablation
Critical to check pt for pregnancy before 131I therapy
Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR

48. Information for Patients Administered Radioactive Iodine (I-131)

49. Homeland security Extremely sensitive radiation detectors are
deployed 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.

50. 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