{"entity":{"id":"i-123","kind":"isotope","name":"Iodine-123","aka":["123I"],"tldr":"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.\n\nIt 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.\n\nBecause 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.","status":"established","asOf":"2026-09-22","links":[{"label":"PMC: perspective on production and quality control of iodine-123","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC12121839/"},{"label":"Radiopaedia: iodine-123","url":"https://radiopaedia.org/articles/iodine-123?lang=us"}],"tags":["gamma emitter","cyclotron","thyroid"],"related":["iobenguane-i-131","i131-mibg","i-124"],"indications":["neuroblastoma","pheochromocytoma-paraganglioma","thyroid"],"sections":[],"technologies":["spect","mibg-theranostics","cyclotron-isotope-production"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"symbol":"123I","element":"Iodine","massNumber":123,"halfLife":"13.2 hours","emissions":["γ 159 keV (83%)","electron capture"],"emissionClass":"gamma","use":"imaging","production":"Cyclotron: 124Xe(p,2n)123Cs → 123Xe → 123I or 124Xe(p,pn)123Xe → 123I on enriched xenon-124 gas targets; alternatively 123Te(p,n)123I on enriched tellurium-123.","supply":"tight","supplyNote":"Requires a medium-energy (20-30 MeV) cyclotron and an expensive enriched xenon-124 or tellurium-123 target, so production is concentrated at a small number of sites worldwide; the 13.2-hour half-life limits shipping range, which has caused regional shortages.","chelators":[],"pairedWith":["i-131"],"since":1970},"route":"/isotopes/i-123/","neighbours":{"drug":[{"id":"i131-mibg","kind":"drug","name":"131I-MIBG (iobenguane I-131) therapy","route":"/drugs/i131-mibg/"},{"id":"f-18-fdopa","kind":"drug","name":"Fluorodopa F-18","route":"/drugs/f-18-fdopa/"},{"id":"i-123-mibg","kind":"drug","name":"Iobenguane I-123","route":"/drugs/i-123-mibg/"},{"id":"i-123-mibg-cardiac","kind":"drug","name":"Iobenguane I-123 (cardiac use)","route":"/drugs/i-123-mibg-cardiac/"},{"id":"iobenguane-i-131","kind":"drug","name":"Iobenguane I-131 (therapeutic)","route":"/drugs/iobenguane-i-131/"},{"id":"i-123-ioflupane","kind":"drug","name":"Ioflupane I-123","route":"/drugs/i-123-ioflupane/"},{"id":"radioactive-iodine","kind":"drug","name":"Radioactive iodine (I-131)","route":"/drugs/radioactive-iodine/"}],"isotope":[{"id":"i-124","kind":"isotope","name":"Iodine-124","route":"/isotopes/i-124/"}],"indication":[{"id":"thyroid-nodule-assessment","kind":"indication","name":"Functional assessment of thyroid nodules","route":"/indications/thyroid-nodule-assessment/"},{"id":"graves-hyperthyroidism","kind":"indication","name":"Graves' disease and hyperthyroidism","route":"/indications/graves-hyperthyroidism/"},{"id":"metastatic-ppgl","kind":"indication","name":"Metastatic pheochromocytoma and paraganglioma","route":"/indications/metastatic-ppgl/"},{"id":"neuroblastoma","kind":"indication","name":"Neuroblastoma (paediatric)","route":"/indications/neuroblastoma/"},{"id":"parkinsonian-syndromes","kind":"indication","name":"Parkinsonian syndromes","route":"/indications/parkinsonian-syndromes/"},{"id":"pheochromocytoma-paraganglioma","kind":"indication","name":"Pheochromocytoma and paraganglioma (PPGL)","route":"/indications/pheochromocytoma-paraganglioma/"},{"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":"mibg-theranostics","kind":"technology","name":"MIBG imaging and 131I-MIBG therapy","route":"/technologies/mibg-theranostics/"},{"id":"radioiodine-therapy","kind":"technology","name":"Radioiodine therapy and whole-body iodine scanning","route":"/technologies/radioiodine-therapy/"},{"id":"spect","kind":"technology","name":"SPECT & bone scan","route":"/technologies/spect/"}],"term":[{"id":"curie-siopen-score","kind":"term","name":"MIBG Curie and SIOPEN scores","route":"/terms/curie-siopen-score/"},{"id":"extravasation-radiopharmaceutical","kind":"term","name":"Radiopharmaceutical extravasation","route":"/terms/extravasation-radiopharmaceutical/"},{"id":"theranostic-pair-term","kind":"term","name":"Theranostic pair","route":"/terms/theranostic-pair-term/"},{"id":"theranostics","kind":"term","name":"Theranostics","route":"/terms/theranostics/"}],"idea":[{"id":"idea-mfbg-pet-replaces-mibg","kind":"idea","name":"18F-MFBG PET replacing 123I-MIBG scintigraphy","route":"/ideas/idea-mfbg-pet-replaces-mibg/"}],"institution":[{"id":"asnc","kind":"institution","name":"American Society of Nuclear Cardiology","route":"/institutions/asnc/"}],"company":[{"id":"bwxt-medical","kind":"company","name":"BWXT Medical","route":"/companies/bwxt-medical/"},{"id":"nihon-medi-physics","kind":"company","name":"Nihon Medi-Physics","route":"/companies/nihon-medi-physics/"},{"id":"pdradiopharma","kind":"company","name":"PDRadiopharma","route":"/companies/pdradiopharma/"}],"target":[{"id":"dopamine-transporter","kind":"target","name":"Dopamine transporter (DAT)","route":"/targets/dopamine-transporter/"},{"id":"norepinephrine-transporter","kind":"target","name":"Norepinephrine transporter (NET)","route":"/targets/norepinephrine-transporter/"}]}}