{"entity":{"id":"i-124","kind":"isotope","name":"Iodine-124","aka":["124I"],"tldr":"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.\n\nIts 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.\n\nIt 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.","status":"emerging","asOf":"2026-09-22","links":[{"label":"PMC: I-124 imaging and dosimetry","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC5283715/"},{"label":"MDPI: radiochemistry, production and immunoPET imaging of iodine-124","url":"https://www.mdpi.com/1420-3049/26/2/414"}],"tags":["positron emitter","long-lived PET","pre-therapy dosimetry"],"related":["radioactive-iodine","i-123"],"indications":["thyroid"],"sections":[],"technologies":["pet","radioligand-dosimetry","cyclotron-isotope-production"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"symbol":"124I","element":"Iodine","massNumber":124,"halfLife":"4.18 days","emissions":["β+ 23% (max ~2.14 MeV)","electron capture ~77%","γ 603 keV (61%)","annihilation γ 511 keV (46%)"],"emissionClass":"positron","use":"imaging","production":"Cyclotron: 124Te(p,n)124I on enriched tellurium-124 (proton energies below ~14 MeV for high radionuclidic purity); older 124Te(d,2n)124I route also used.","supply":"constrained","supplyNote":"Low reaction yield and the need for an expensive enriched tellurium-124 target mean 124I is produced at only a limited number of cyclotron centres, mostly for dosimetry research and thyroid-cancer pre-therapy planning rather than routine clinical stock.","chelators":[],"pairedWith":["i-131"],"since":1994},"route":"/isotopes/i-124/","neighbours":{"drug":[{"id":"radioactive-iodine","kind":"drug","name":"Radioactive iodine (I-131)","route":"/drugs/radioactive-iodine/"}],"isotope":[{"id":"i-123","kind":"isotope","name":"Iodine-123","route":"/isotopes/i-123/"}],"indication":[{"id":"thyroid","kind":"indication","name":"Thyroid cancer","route":"/indications/thyroid/"}],"technology":[{"id":"cyclotron-isotope-production","kind":"technology","name":"Cyclotron isotope production (F-18, Ga-68, Cu-64, Zr-89, At-211)","route":"/technologies/cyclotron-isotope-production/"},{"id":"pet","kind":"technology","name":"PET (positron emission tomography)","route":"/technologies/pet/"},{"id":"radioligand-dosimetry","kind":"technology","name":"Radioligand dosimetry","route":"/technologies/radioligand-dosimetry/"}],"opportunity":[{"id":"opp-cldn18-2-imaging-gastric","kind":"opportunity","name":"Claudin-18.2 imaging when one biopsy says negative","route":"/opportunities/opp-cldn18-2-imaging-gastric/"}],"person":[{"id":"dale-bailey","kind":"person","name":"Dale L. Bailey","route":"/people/dale-bailey/"}],"target":[{"id":"cldn18-2","kind":"target","name":"Claudin-18.2","route":"/targets/cldn18-2/"}]}}