1. Nuclear Radiology Thyroid

2. I-123 I-131 Physical T ½ = 13 hours Principal Gamma = 159 KeV
Better imaging characteristics, lower dosimetry, cyclotron produced – more expensive.
For imaging and RAIU calculation.
Dosing ranges from 0.4 – 5.0 mCi
Physics T ½ = 8.1 days
Effective T ½ = 5 days
Principal Gamma = 364 KeV
Principal Beta (-) = 0.4mm range in soft tissue.
90% of the ionizing therapeutic effects come from Betas, the remainder from the Gammas.
Nuclear reactor byproduct – cheap.
For Treatment.
Imaging primarily as an incidental opportunity after a therapy dose.
Dosing ranges from mCi at any one time (can re-treat with a lot of care )

4. GRAVE’S
Autoimmune disorder – body makes immunoglobulins binding to thyroid hormone receptors, mimicking TSH – causes gland hypertrophy and excessive production of T3/T4 independent of the normal feedback mechanism.
TSH = LOW
RAIU = HIGH as a kite

5. Toxic Autonomous Adenoma
Etiology is from genetic mutations of TSH receptors in the cell surfaces, resulting in continuous activations.
Normal gland is suppressed
TSH = LOW
RAIU = Moderately elevated or upper range of normal.

6. Toxic Multinodular Goiter
1 or more toxic adenomas go rogue, don’t respond to feedback. Normal gland tissue is suppressed due to excess T3 and T4 secreted by adenomas.
Often in Elderly

7. Thyroiditis
Inflammation causes release of the normal gland’s stores of T3/T4. Normal feedback mechanism applies.
Patient is hyperthyroid due to released hormones.
TSH = LOW
RAIU = LOW (Inflamed thyroid finds it hard to transport or organify.)

9. Dose Calculation ( Z x Size of thyroid [g] x 100 ) / RAIU = Dose [mCi]
Where “Z” is the desired activity (in micro-Curies) per gram you want to hit the thyroid with, which is typically 160.
Therefore . . .
( 160 x Size of thyroid [g] x 100 ) / RAIU = Dose [mCi]
Size of Thyroid can be painstakingly measured sonographically or guesstimated by palpation by the endocrinologist: MAKES NO DIFFERENCE !!!
For mental reference: a NORMAL thyroid goes approximately g. A goiter can go up to 40 or more.

10. Treatment Doses for Hyperthyroidism
Grave’s Disease
TMNG & Autonomous Nodule
8-15 mCi
20 mCi

11. Simplified Fixed Dose for Thyroid CANCER:
Tumors < 1cm and no high risk features = NO Post-Op I-131 Indicated
Low Risk and Age < 45 = 50 mCi
Low Risk and Age > 45 = 75 mCi
Intermediate Risk = 100 mCi
High Risk = 150 mCi
Known Distant Mets = 200 mCi

12. LOW Recurrence Risk
Clean margins on resection and no spread whatsoever. NO vascular of lymph node invasion.
NO aggressive histology (tall cell, insular, columnar cell).
NO I-123 Whole Body (postop) uptake outside the thyroid bed.

13. INTERMEDIATE Risk Microscopic invasion into perithyroidal tissue
Cervical nodal metastases, vascular invasion or aggressive histology (tall cell, insular, columnar cell).
I-123 uptake outside of thyroid bed on Post-Op scan.

14. HIGH Risk Macroscopic (naked eye) invasion Incomplete tumor resection
Distant metastases.
Thyroglobulin levels much higher than findings seen on post-op I-131 scan.