# Iodine-123

Source: https://nuclide.cc/isotopes/i-123/  
Nuclide record `i-123` (Isotope). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

A radioactive form of iodine that decays quickly and gives off gamma rays, used to take a picture of the thyroid or, attached to a nerve-tracing molecule, of tumours of the adrenal gland and nervous system, before deciding whether a therapeutic dose of iodine-131 makes sense.

## Summary

Iodine-123 has a 13.2-hour half-life and decays by electron capture with a dominant 159 keV gamma emission well suited to gamma-camera and SPECT imaging. Its main clinical roles are thyroid uptake and scintigraphy, and as the diagnostic imaging partner to iobenguane (MIBG): 123I-MIBG scintigraphy stages neuroblastoma and phaeochromocytoma/paraganglioma before or alongside treatment with the therapeutic 131I-MIBG.

It is cyclotron-produced, never reactor-produced, most commonly via 124Xe(p,2n)123Cs, which decays through 123Xe to 123I, or via the (p,pn) channel on the same enriched xenon-124 target; a 123Te(p,n)123I route on enriched tellurium is also used. Both routes need a medium-energy cyclotron (20-30 MeV) and an expensive enriched target, which keeps 123I costlier and less universally available than reactor- or generator-based isotopes, and its 13-hour half-life limits how far it can be shipped before it has decayed away.

Because iodine's biochemistry is essentially identical across its isotopes, 123I plays the same diagnostic-before-therapeutic role for iodine and MIBG imaging that 68Ga and 18F play for peptide and small-molecule theranostics.

## Fields

- Kind: Isotope
- Status: established
- Last checked: 2026-09-22
- Also known as: 123I
- Tags: gamma emitter; cyclotron; thyroid

## Sources

- PMC: perspective on production and quality control of iodine-123: https://pmc.ncbi.nlm.nih.gov/articles/PMC12121839/
- Radiopaedia: iodine-123: https://radiopaedia.org/articles/iodine-123?lang=us

## Connected records

- drugs: [131I-MIBG (iobenguane I-131) therapy](https://nuclide.cc/drugs/i131-mibg/), [Fluorodopa F-18](https://nuclide.cc/drugs/f-18-fdopa/), [Iobenguane I-123](https://nuclide.cc/drugs/i-123-mibg/), [Iobenguane I-123 (cardiac use)](https://nuclide.cc/drugs/i-123-mibg-cardiac/), [Iobenguane I-131 (therapeutic)](https://nuclide.cc/drugs/iobenguane-i-131/), [Ioflupane I-123](https://nuclide.cc/drugs/i-123-ioflupane/), [Radioactive iodine (I-131)](https://nuclide.cc/drugs/radioactive-iodine/)
- isotopes: [Iodine-124](https://nuclide.cc/isotopes/i-124/)
- indications: [Functional assessment of thyroid nodules](https://nuclide.cc/indications/thyroid-nodule-assessment/), [Graves' disease and hyperthyroidism](https://nuclide.cc/indications/graves-hyperthyroidism/), [Metastatic pheochromocytoma and paraganglioma](https://nuclide.cc/indications/metastatic-ppgl/), [Neuroblastoma (paediatric)](https://nuclide.cc/indications/neuroblastoma/), [Parkinsonian syndromes](https://nuclide.cc/indications/parkinsonian-syndromes/), [Pheochromocytoma and paraganglioma (PPGL)](https://nuclide.cc/indications/pheochromocytoma-paraganglioma/), [Thyroid cancer](https://nuclide.cc/indications/thyroid/)
- technologies: [Cyclotron isotope production (F-18, Ga-68, Cu-64, Zr-89, At-211)](https://nuclide.cc/technologies/cyclotron-isotope-production/), [MIBG imaging and 131I-MIBG therapy](https://nuclide.cc/technologies/mibg-theranostics/), [Radioiodine therapy and whole-body iodine scanning](https://nuclide.cc/technologies/radioiodine-therapy/), [SPECT & bone scan](https://nuclide.cc/technologies/spect/)
- terms: [MIBG Curie and SIOPEN scores](https://nuclide.cc/terms/curie-siopen-score/), [Radiopharmaceutical extravasation](https://nuclide.cc/terms/extravasation-radiopharmaceutical/), [Theranostic pair](https://nuclide.cc/terms/theranostic-pair-term/), [Theranostics](https://nuclide.cc/terms/theranostics/)
- ideas: [18F-MFBG PET replacing 123I-MIBG scintigraphy](https://nuclide.cc/ideas/idea-mfbg-pet-replaces-mibg/)
- institutions: [American Society of Nuclear Cardiology](https://nuclide.cc/institutions/asnc/)
- companies: [BWXT Medical](https://nuclide.cc/companies/bwxt-medical/), [Nihon Medi-Physics](https://nuclide.cc/companies/nihon-medi-physics/), [PDRadiopharma](https://nuclide.cc/companies/pdradiopharma/)
- targets: [Dopamine transporter (DAT)](https://nuclide.cc/targets/dopamine-transporter/), [Norepinephrine transporter (NET)](https://nuclide.cc/targets/norepinephrine-transporter/)

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JSON: https://nuclide.cc/api/v1/entities/i-123.json