# Iodine-124

Source: https://nuclide.cc/isotopes/i-124/  
Nuclide record `i-124` (Isotope). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

A long-lived, PET-visible form of radioactive iodine used to map how a thyroid cancer takes up iodine over several days, so the dose of the treatment isotope, iodine-131, can be planned before it is given.

## Summary

Iodine-124 decays with a 4.18-day half-life by a mix of electron capture and positron emission (positron abundance about 23%), giving it PET-imageable annihilation photons over a timescale of days rather than the minutes-to-hours typical of most PET isotopes. Because it shares iodine's biochemistry with the therapeutic isotope 131I, serial 124I PET/CT scans, typically at roughly 24 and 96-120 hours after a tracer dose, let physicists build a time-activity curve for each lesion and project the absorbed dose per unit of a subsequent 131I therapy activity, rather than relying on a fixed empiric dose.

Its decay scheme is complex: only about 23% of decays produce a positron (mean energy 819 keV, giving relatively poor spatial resolution), while high-energy prompt gammas (603 keV and others) contaminate the coincidence signal, so scanners need isotope-specific calibration rather than the F-18 calibration used by default; published work has found this calibration factor can differ from F-18 by roughly ten percent.

It is cyclotron-produced by proton bombardment of enriched tellurium-124, 124Te(p,n)124I, chosen for high radionuclidic purity at proton energies below about 14 MeV, though yields from this reaction are comparatively low, and by the older 124Te(d,2n)124I route.

## Fields

- Kind: Isotope
- Status: emerging
- Last checked: 2026-09-22
- Also known as: 124I
- Tags: positron emitter; long-lived PET; pre-therapy dosimetry

## Sources

- PMC: I-124 imaging and dosimetry: https://pmc.ncbi.nlm.nih.gov/articles/PMC5283715/
- MDPI: radiochemistry, production and immunoPET imaging of iodine-124: https://www.mdpi.com/1420-3049/26/2/414

## Connected records

- drugs: [Radioactive iodine (I-131)](https://nuclide.cc/drugs/radioactive-iodine/)
- isotopes: [Iodine-123](https://nuclide.cc/isotopes/i-123/)
- indications: [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/), [PET (positron emission tomography)](https://nuclide.cc/technologies/pet/), [Radioligand dosimetry](https://nuclide.cc/technologies/radioligand-dosimetry/)
- opportunities: [Claudin-18.2 imaging when one biopsy says negative](https://nuclide.cc/opportunities/opp-cldn18-2-imaging-gastric/)
- people: [Dale L. Bailey](https://nuclide.cc/people/dale-bailey/)
- targets: [Claudin-18.2](https://nuclide.cc/targets/cldn18-2/)

---
JSON: https://nuclide.cc/api/v1/entities/i-124.json