This is additional treatment that is sometimes given to reduce the risk for cancer recurrence or to treat presumed residual cancer.
- This is a one-time pill typically given 2-3 months following surgery.
Iodine is a substance that is almost exclusively absorbed by thyroid cells in the body.
- A special kind of iodine (I) can be produced called I-131.
- I-131 emits radiation which can kill the thyroid cells that absorb it as well as nearby thyroid cells several millimeters away.
- Therefore, RAI can act like a ‘heat-seeking missile,’ specifically targeting thyroid cells (both normal and cancerous), while decreasing risk of damage to other types of cells in the body (limiting side effects).
- Absorption of iodine is compromised in Non-Well Differentiated Thyroid Cancers (nWDTC’s) and is therefore not effective and not indicated as treatment in these rare types of thyroid cancers.
If only a hemithyroidectomy was performed, a completion thyroidectomy (removal of the remaining half of the thyroid) must be performed prior to receiving RAI.
- If a normal half of a thyroid remains in the body, the RAI will predominantly attack the normal thyroid lobe and be less effective against possible residual thyroid cancer cells.
Goal of giving RAI:
- Destroy any residual thyroid tissue (aka remnant ablation).
- Allows post-surgery thyroglobulin level measurements to be more sensitive.
- Any thyroglobulin detected after receiving RAI is likely to be from cancer cells and not normal thyroid cells.
- Typical dose around 30 mCi.
- Destroy suspected microscopic residual cancer to decrease risk of recurrence.
- Referred to as adjuvant therapy.
- Not effective for cancer > 1.0 cm.
- Typical dose around 150 mCi.
Indications are based on features seen on the pathology report (American Thyroid Association Risk Stratification System) and thyroglobulin (tumor marker) levels measured in the blood 6 weeks following surgery.
- Recommended in cancers with high risk for recurrence.
- Shown to improve overall survival in these patients.
- Consideration for intermediate risk for recurrence based on thyroglobulin levels 6 weeks after surgery.
Type of mutation driving WDTC’s can also impact the effectiveness of RAI.
- This is determined by gene sequencing or molecular analysis of the thyroid cancer cells.
- RAS variants (Follicular Thyroid Cancer or follicular-variant of Papillary Thyroid Cancer) retain iodine absorption fairly well and can typically respond to repeated doses of RAI.
- BFRAF variants (classic and tall-cell variant of Papillary Thyroid Cancer) can become refractory to RAI in patients who have persistent cancer.
RAI is prescribed and administered by an Endocrinologist.
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