# Radioiodine therapy (I-131)

Source: https://onco.cc/terms/radioiodine-term/  
OnCo record `radioiodine-term` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Swallowing a capsule of radioactive iodine after thyroid surgery: thyroid cells (including cancer cells) are the only ones that soak up iodine, so the radiation destroys leftover thyroid tissue and metastases while sparing everything else. It was the first targeted radiotherapy, in 1946.

## Summary

Differentiated (papillary and follicular) thyroid cancer retains iodine uptake, so I-131 ablates remnant tissue after total thyroidectomy in intermediate- and high-risk patients and treats iodine-avid metastases; low-risk patients no longer need it (ESTIMABL2, IoN). Thyroglobulin and whole-body scans monitor for recurrence. 'Radioiodine-refractory' disease (about 5-15%, more in poorly differentiated and BRAF-mutant tumours) is treated with lenvatinib, sorafenib or targeted drugs for RET, NTRK and BRAF alterations, and MEK/BRAF inhibitors can restore iodine uptake ('redifferentiation'). Side effects are salivary gland damage, dry mouth and a small excess of secondary cancers at high cumulative doses.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: radioiodine; radioactive iodine; radioiodine ablation; radioiodine therapy; I-131; 131I; iodine-131; RAI-refractory; radioiodine-refractory; RAI-avid; radioiodine-avid; iodine-avid; iodine uptake; redifferentiation; recombinant TSH; rhTSH

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Iodine-131
- Wikipedia: https://en.wikipedia.org/wiki/Iodine-131

## Connected records

- technologies: [Peptide receptor radionuclide therapy (PRRT)](https://onco.cc/technologies/prrt/), [Radioiodine therapy and whole-body iodine scanning](https://onco.cc/technologies/radioiodine-therapy/)
- terms: [Theranostics](https://onco.cc/terms/theranostics/), [Thyroidectomy](https://onco.cc/terms/thyroidectomy/), [Tumour markers (CEA, LDH, chromogranin, thyroglobulin)](https://onco.cc/terms/tumour-markers/)
- cancers: [Thyroid cancer](https://onco.cc/cancers/thyroid/)
- fronts: [Radiopharmaceuticals & Theranostics](https://onco.cc/fronts/radiopharma/)
- drugs: [131I-MIBG (iobenguane I-131) therapy](https://onco.cc/drugs/i131-mibg/), [Lenvatinib](https://onco.cc/drugs/lenvatinib/), [Radioactive iodine (I-131)](https://onco.cc/drugs/radioactive-iodine/), [Sorafenib](https://onco.cc/drugs/sorafenib/), [Thyrotropin alfa](https://onco.cc/drugs/thyrotropin-alfa/)

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