Nuclear Medicine in Thyroidology


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Nuclear Medicine in Thyroidology

  1. 1. Nuclear Medicine in thyroid imaging and therapy
  2. 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. 3. Nuclear Medicine techniques provide this functional information that can be vital in early diagnosis and can help in appropriate management
  4. 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
  6. 6. Normal thyroid
  7. 7. Isotopes in Thyroidology  DIAGNOSTIC ROLE: In-Vivo imaging: Pre and post operative scans In-Vitro tests: Hormone assays  THERAPEAUTIC ROLE
  8. 8. 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
  9. 9. 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.
  12. 12. Hot nodule (AFTN) Cold nodule Normal thyroid scan
  14. 14. Adult female with dysphagia: I-123 scan An enlarged thyroid (thyromegaly) is often discovered on chest radiography.
  15. 15. Ectopic thyroid
  16. 16. 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”
  17. 17. 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
  18. 18. 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
  19. 19. 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
  20. 20. 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”
  21. 21. 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
  22. 22. 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
  23. 23. 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
  24. 24. Factors affecting the dose given • Gland size • Maximal uptake • Biological/ effective half life of I-131
  25. 25. 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
  26. 26. 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
  27. 27. Portable ionosation chamber based radiation survey meter Fumehood
  28. 28. 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
  29. 29. Radioiodine treatment of thyroid cancer
  30. 30. A New Dimension………  Keston et al in 1942 : Demonstrated concentration of I-131 in theThyroid Cancer
  31. 31. Guidelines in literature •American Association of Clinical Endocrinologists •American Association of Endocrine Surgeons •British Thyroid Association •Royal College of Physicians •National Comprehensive Cancer Network
  32. 32. 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
  33. 33. •Most predictive factors: Presence of distant mets., Age Extent of tumor Differentiated Thyroid Cancer
  34. 34. 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.
  35. 35. 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.
  36. 36. rhTSH protocol Cornell Medical Centre NY USA
  37. 37. Post-operative Radio-iodine Scan  To determine residual thyroid tissue  To determine metastatic disease  To determine the suitability for Radio- iodine therapy
  38. 38. C/o PTC post total thyroidectomy Radioiodine (I-131) scan
  39. 39. 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)
  40. 40. 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
  41. 41. Radioiodine therapy is unique since it requires attention to radiation safety procedures necessitating hospitalization and isolation of patient in radiation ward
  42. 42. 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
  43. 43. 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)
  44. 44. 87% vs 49% after 10 years Thyroid cancer related survival 93% vs 78% after 10 years
  45. 45. Comparison of cumulative deaths in in pts with PCT: Surgery alone vs Surgery and thyroid hormone vs thyroidectomy and RRA
  46. 46. Two negative annual successive whole body scans have very good predictive value for a lack of future recurrence Follow up strategy (post surgery & RRA)
  47. 47. CARCINOMA THYROID WITH EXTENSIVE METS Gaurav Malhotra Metastatic parotid tumor: A rare presentation for papillary carcinoma of thyroid. Clin Nucl Med. 2007 Jun;32(6):488-90.
  48. 48. 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
  49. 49. 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
  50. 50. 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.
  51. 51. 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.
  52. 52. 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?
  53. 53. 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?
  54. 54. 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?
  55. 55. 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
  56. 56. 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
  57. 57. "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
  58. 58. THANK YOU