Nuclear medicine techniques such as radioactive iodine scans and therapy are important in evaluating and treating thyroid diseases. Radioactive iodine is selectively taken up and concentrated in the thyroid gland, allowing functional imaging and selective internal radiotherapy for hyperthyroidism and thyroid cancer. Radioactive iodine therapy is the primary treatment for Graves' disease and toxic multinodular goiter. It is also used to ablate residual thyroid tissue after surgery and treat thyroid cancer metastases. Precautions must be taken after radioactive iodine therapy to limit radiation exposure to others.

1. Nuclear Medicine in thyroid imaging
and therapy

2. What is Nuclear Medicine?
Branch of Medicine in which patients are
given radioactive substances (to be taken
internally) either to diagnose or to treat a
disease.
Differs from traditional radiology or
radiotherapy techniques, where radiation is
normally applied from an external source.

3. Nuclear Medicine techniques provide this functional information
that can be vital in early diagnosis and can help in appropriate
management

4. Nuclear medicine: FUNCTIONAL
IMAGING
Most other imaging modalities:
STRUCTURAL OR ANATOMICAL
IMAGING
Nuclear medicine images can be
superimposed on images from
modalities such as CT or MRI to
highlight which part of the body the
radiopharmaceutical is concentrated
in: IMAGE FUSION OR
COREGISTRATION

5. MOLECULAR AND MORPHOLOGIC IMAGING

7. Normal thyroid

8. Isotopes in Thyroidology
 DIAGNOSTIC ROLE:
In-Vivo imaging: Pre and post operative scans
In-Vitro tests: Hormone assays
 THERAPEAUTIC ROLE

9. Types Of Scans in Thyroidology
1. MORPHOLOGICAL SCAN:99TcO4(pertechnetate
scan): assess size, shape and nature of nodule
2. METABOLIC SCAN: Radioiodine scan(131/123),
18 FDG PET scan
3.RECEPTOR SCAN: 131/123-MIBG scan
4.NON-SPECIFIC SCAN: Thallium scan, DMSA(V)scan,
Sestamibi scan
5.FUSION IMAGING: CT & Isotope scan FUSED image

10. Routine Thyroid Scan
 99mTcO4(pertechnetate scan):
- 6hours half-life & hence less radiation dose,
ideal for all age group
- isotope is trapped by thyrocytes and is NOT
further organified
- is ideal for assessing size,shape and nature
of nodule.

11. INDICATIONS IN THYROIDOLOGY
 SOLITARY THYROID NODULE
 THYROTOXICOSIS--- Graves’ vs Thyroiditis
 ECTOPICTHYROID
 AGENESIS OFTHYROID
 THYROID CANCER FOLLOWUP
 RETROSTERNAL GOITRE

12. THYROIDITIS vs THYROTOXICOSIS

14. Hot nodule (AFTN)
Cold
nodule
Normal thyroid scan

15. •Colloid nodules may be either mono or polyclonal
•THUS TUMORS REPRESENT THE PERSISTENT GROWTH OF THE
PROGENY OF ONE CELL THAT HAS SOMEHOW ESCAPED THE
MECHANISMS WHICH MAINTAIN THE NORMAL CELL DIVISION AT
ABOUT ONCE IN EACH 8.5 YEARS
Tc-99m scanI-131 scan

16. Adult female with
dysphagia: I-123 scan
An enlarged thyroid
(thyromegaly) is often
discovered on chest
radiography.

17. Ectopic thyroid

18. Radio-iodine scan(I-131/I-123)
 Invented by Prof.Robley Evans from MIT
 First isotope used for imaging in humans
 Chemically analogous to stable iodine which
is preferentially handled by thyroid & hence
called “metabolic scan”

19. Isotope is trapped by thyrocytes (Na I Symporter or NIS) and further undergoes
organification into MIT,DIT and thyroxine formation. Hence uptake indicates the
function of thyrocytes.
Normal NIS protein expression is limited to basolateral membrane in a small % of
thyroid follicular cells at any one time
Radio-iodine: Mechanism of
uptake

20. I-131
 I-131 has 8 days half life
& both beta and gamma
radiations—hence more
radiation to thyroid
than fromTcO4 scan
•Scan has to be done after 48hours of isotope
administration whereas Tc scan is done30min after
isotope(one visit)
•Not ideal for children
•Ideal for ectopic thyroid scanning, functional
assessment, thyroid cancer

21. I-123
 Expensive isotope, Not available in India
 Has 100 min half life,only gamma radiation &
hence better than both 131-I &Tc scans
 Trapping and organification of iodine by
thyrocyte provides a unique opportunity for
“internal selective radiotherapy” in context of
“metabolic radionuclide therapy” with low dose to
other organs
I-131

22. Radioactive iodine (RAI) therapy
for Benign thyroid diseases
 RAI (I-131) therapy has been used for over 50 years
 Graves’ disease
 Solitary hyperfunctioning nodule
 Toxic MNG
 RAI may also benefit pts. of subclinical hyperthyroidism
particularly patients at a risk for cardiac or systemic
complications
 RAI treatment leads to long standing reduction in
thyroid function and thyroid volume and has been
aptly termed as “unbloody thyroid surgery”

23. Mechanism of action of I-131
• RAI with I-131 relies on emission of high energy
beta particles to cause damage to thyroid gland
tissue  local inflammation & fibrosis 
reduction of synthetic capacity of the thyroid
gland.
• For this therapy to be effective thyroid tissue must
accumulate and retain iodine long enough for
adequate amounts of radiation to be delivered

24. Contraindications to I-131
RAI has no role for treatment of hyperthyroid
conditions that are self limited or when thyroid
tissue is not hyperfunctioning
Silent, subacute & postpartum thyroiditis in
addition to factitious thyroid disease
Pregnancy and lactation: Absolute C/I

25. What dose of radioiodine is
used?
• Dosimeteric approach
• Emperical treatment
Regardless of method for dose selection routine
RAIU is useful for confirming hyperfunctioning
gland prior to therapy.
RAIU can also help exclude a hyperfunctioning
gland with blocked uptake

26. Factors affecting the dose
given
• Gland size
• Maximal uptake
• Biological/ effective half life of I-131

27. RAI therapy: Concepts
• 80-200 microcurie per gram of thyroid tissue
assuming a biological half life of 4-6 days delivers a
dose of 50 to 100 Gray to thyroid
• Higher dose required for retreatment (typically 3 to
6 months after initial treatment)
• Previous RAI tr failure does not lessen the chance of
successful retreatment
• Treatment based on calculations appear efficacious
but have not been proven superior to empirical
treatment

28. RAI therapy: Concepts
• Capsule vs Liquid formulations (I-131)
• Liquid formulations require extra measures
to minimize radiation contamination at the
time of administration
• Equivalent in efficacy

30. Portable
ionosation
chamber based
radiation
survey meter
Fumehood

32. Treatment outcome
• Expected response rate in about 80% pt.
• 20-40% pt. hypo 1 year after RAI
Side effects: Mild, infrequent and self limiting; thyroid
tenderness salivary gland swelling and nausea

33. Radioiodine treatment of thyroid
cancer

34. A New Dimension………
 Keston et al in 1942 :
Demonstrated
concentration of I-131
in theThyroid Cancer

35. Guidelines in literature
•American Association of Clinical
Endocrinologists
•American Association of Endocrine
Surgeons
•British Thyroid Association
•Royal College of Physicians
•National Comprehensive Cancer
Network

36. Problems in guidelines…?
•Provide conflicting recommendations
because of lack of high quality evidence from
Randomized Control Trials
•‘American Thyroid Association guidelines’
–For management of patients of thyroid nodules
and carcinoma
–Used strategy similar to NIH
–Thyroid Vol. 16 No.2, 2006

38. •Most predictive factors:
Presence of distant mets.,
Age
Extent of tumor
Differentiated Thyroid Cancer

39. Ref: AJCC Cancer staging manual 6th
edition (2002)
Radioiodine ablation recommended for pt. with:
Stage III & IV dis.
Stage II, >= 45 yr
Stage I (selected pt.): Multifocal, nodal mets,
aggressive histopath, ETE, vasc. Inv.

41. No uptake
No treatment**
F/U after 6 months
**Provided that
1Iodide interference is
ruled out
2Histopathology not
aggressive (follicular
carcinoma, aggressive
variants papillary
carcinoma)
Remnant thyroidal bed uptake
Treat
F/U after 6 months for large
dose scan with 3-5 mCi of I-
131
•Off Eltroxin 4-6 Weeks
•TSH, Tg, Sr. Ca, US neck
•Chest and neck X-ray
No abnormal uptake
F/U after 1 yr on Eltroxin
•Tg and USG neck
RMC Protocol following total thyroidectomy
100uCi I-131 uptake and scan with radioiodine With metastasis
Treat
F/U after 6 months for
large dose scan with 3-5
mCi of I-131
•Off Eltroxin 4-6 Weeks
•TSH, Tg, Sr. Carcinoma
•Chest and neck X-ray
Abnormal concentration
Treat
F/U after 1 year for large
dose scan
•Off Eltroxin
•TSH, Tg, Sr. Ca
•Chest and neck X-ray
Off thyroxine for 4-6 wks, No iodine containing drugs, food, Measure TSH & Tg,
Chest & neck X-ray, pathology review.

42. rhTSH protocol Cornell Medical Centre NY USA

43. Post-operative Radio-iodine
Scan
 To determine residual thyroid tissue
 To determine metastatic disease
 To determine the suitability for Radio-
iodine therapy

44. C/o PTC post
total
thyroidectomy
Radioiodine
(I-131) scan

45. Radioiodine treatment
•Outcome of I-131 therapy: Related to the
effective radiation dose delivered to thyroid
cancer tissue
•Most of the radiation dose is delivered by
beta particles that do not penetrate deep
into the tissue (2 mm in depth at the most)

46. Radioiodine therapy
•Emperical therapy
•Dosimetric approach
In pts in whom RRA is planned there has been a trend
towards reduction in dose of I-131 administered: 30-50
mCi in present decade as compared to 150-250 mCi
with no difference in therapy outcome. As a result there
has been lesser undesirable radiation exposure and
reduction in stay in the isolation ward

47. Radioiodine therapy is unique
since it requires attention to
radiation safety procedures
necessitating hospitalization and
isolation of patient in radiation
ward

48. Patient is discharged when whole body retention of radioactivity is
less than 555 MBq (AERB) a limit ensured and established by patient
monitoring using a portable ionization chamber based radiation
survey meter

49. I 131 scan
Initial scan
following surgery
Follow up scan following residual
remnant ablation (RRA)
No clinical evidence of tumor
No imaging evidence of tumor (no uptake outside
thyroid bed on initial post treatment scan, on a
recent diag. scan, or neck US)
Undetectable serum TG (tumor marker)

50. 87% vs 49% after 10 years Thyroid cancer related survival
93% vs 78% after 10 years

51. Comparison of cumulative deaths in in pts with PCT: Surgery alone vs
Surgery and thyroid hormone vs thyroidectomy and RRA

52. Two negative annual successive
whole body scans have very
good predictive value for a lack
of future recurrence
Follow up strategy (post
surgery & RRA)

53. CARCINOMA THYROID WITH EXTENSIVE METS
Gaurav Malhotra et.al. Metastatic parotid tumor: A rare presentation for
papillary carcinoma of thyroid. Clin Nucl Med. 2007 Jun;32(6):488-90.

54. 52 yr male a known case of follicular carcinoma of thyroid was
administered 182 mCi of radioiodine a month after total
thyroidectomy.
Post therapy scan: Radioiodine uptake in apex of left lung

55. CT guided biopsy of mass revealed mucinous BAC. Surgery was ruled out so he was
given chemotherapy without benefit. Since the lesion continued to show I-131 uptake a
high dose radioiodine therapy was given with 209 mCi I-131. Follow up CT scan
showed 1 cm all round reduction of the mass suggesting a possibility of this therapeutic
option in non thyroidal tumors that may concentrate radioiodine

56. 30 yr male underwent total
thyroidectomy followed by RAI
therapy for PTC.
Presented 2 decades later with
LBA. MRI s/o multiple vertebral
mets. WB RAI scan showed
extensive mets and suspicious
abdominal foci.

58. CT guided biopsy from left adrenal focus confirmed
metastasis from carcinoma of thyroid.
Metastases to both renal and adrenal have been
rarely reported from carcinoma of thyroid and to the
best of our knowledge this the second such case.

59. Pertinent questions
1. Multicentre retrospective cohort study examined
cancer mortality in >35,000 patients after 3
treatment modalities for hyperthyroidism: Total
cancer deaths not increased for this group. RAI not
associated with excess total cancer deaths
2. Incidence of thyroid ca in RAI treated patients
over 27 year period was not significantly
different from general population incidence
Does radioiodine treatment cause cancer?

60. Pertinent questions
• I-131 delivers a dose of 0.01-0.03 Gy to ovaries
mostly from excreted iodine in bladder
• No adverse outcome in subsequent pregnancies
has been seen
• Avoid pregnancy for atleast 6 months following
therapy
Does radioiodine treatment have adverse genetic
effects on offsprings?

61. Pertinent questions
• Sleep alone for a few days
• >3 feet distance from others in first 72 hrs
• Avoid contact with children and pregnant
women
• Hydration/ toilet/ Clothes/ utensils
What precautions does the patient have to follow
after receiving RAI?

62. Pertinent questions
• What is the best time to assess the response of RAI
therapy?
•For thyrotoxicosis pts: Assessment of treatment
response is more reliable at 12 to 14 weeks of
therapy although it may be possible to identify
non-optimal responder at 6 to 8 weeks

63. Thyroid cancer with all its
peculiarities in biological and
histological criteria should be
treated as any other cancer: get rid
of the tumor and do everything to
avoid recurrence or mets; treat
mets as well and as long as you can

64. "Anyone who stops learning is old,
whether at 20 or 80.
Anyone who keeps learning stays young.
The greatest thing in life is
to keep your mind young„
Henry Ford

65. THANK YOU