# Actinium-225

Source: https://nuclide.cc/isotopes/ac-225/  
Nuclide record `ac-225` (Isotope). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

A metal that fires off very powerful, very short-range radioactive particles as it decays through a chain of daughter atoms. Because the particles barely travel beyond the cell they hit, it can kill a cancer cell while leaving neighbouring healthy cells mostly untouched. Supply is scarce, so it is still mostly used in research studies.

## Summary

Actinium-225 decays by alpha emission through six short-lived daughters to stable bismuth-209, releasing a net four alpha particles per decay (a 'nanogenerator'). At 9.9 days its half-life is long enough for centralised manufacture and international shipping, unlike its short-lived daughter bismuth-213.

The historical route extracts 225Ac from decaying stockpiles of thorium-229 (itself from aged uranium-233), 'milked' every few weeks; the amounts are milligram/curie-scale and cannot be scaled much further. Newer accelerator routes -- proton spallation of thorium-232, or proton irradiation of radium-226 targets via 226Ra(p,2n)225Ac -- are being industrialised by the DOE's Tri-Lab effort (Brookhaven, Los Alamos, Oak Ridge) and by companies building cyclotron and linac capacity.

Supply is the most contested number in the field. A 2023 Journal of Nuclear Medicine analysis put worldwide 229Th/225Ac-derived supply at roughly 63 GBq (1.7 Ci) per year, enough for only 100-200 patients, against a stated need for hundreds to thousands of curies a year if approved 225Ac drugs reach broad use; it projected accelerator and photonuclear routes could reach over 25 TBq (670 Ci) a year worldwide by 2032. Other DOE and IAEA figures from 2013-2021 cite current 229Th-derived supply at 1-2 Ci/year (37-74 GBq) split mainly between Oak Ridge National Laboratory (ORNL, USA), the Joint Research Centre in Karlsruhe (Germany, ~13 GBq/year) and IPPE Obninsk (Russia, ~22 GBq/year), and note the same production facilities co-produce the long-lived impurity 227Ac (half-life 21.8 years) at the 0.1-0.2% level, which complicates waste handling and dosimetry.

## Fields

- Kind: Isotope
- Status: phase-2
- Last checked: 2026-09-22
- Also known as: 225Ac; Ac-225
- Tags: therapy; alpha emitter; supply-constrained

## Sources

- Is Actinium Really Happening? (Journal of Nuclear Medicine, 2023): https://jnm.snmjournals.org/content/64/10/1516
- DOE Isotope Program: Production Methods for Ac-225: https://www.isotopes.gov/information/actinium-225
- Supply and Clinical Application of Actinium-225 and Bismuth-213 (PMC, 2020): https://pmc.ncbi.nlm.nih.gov/articles/PMC7082773/
- Actinium-225 in targeted alpha-particle therapeutic applications (PMC): https://pmc.ncbi.nlm.nih.gov/articles/PMC5565267/

## Connected records

- drugs: [AAA817](https://nuclide.cc/drugs/aaa817/), [Actinium-225 DOTATATE](https://nuclide.cc/drugs/ryz101/), [Actinium-225 FPI-2068](https://nuclide.cc/drugs/ac-225-fpi-2068/), [Actinium-225 PSMA agents](https://nuclide.cc/drugs/ac225-psma/), [FPI-2265](https://nuclide.cc/drugs/fpi-2265/)
- technologies: [Actinium-225 supply: thorium stocks, accelerators and radium targets](https://nuclide.cc/technologies/actinium-225-supply/), [Alpha-emitter daughter redistribution ('free daughter' problem)](https://nuclide.cc/technologies/alpha-daughter-redistribution/), [Alpha-emitter nanogenerators and daughter trapping](https://nuclide.cc/technologies/alpha-nanogenerators/), [Cyclotron isotope production (F-18, Ga-68, Cu-64, Zr-89, At-211)](https://nuclide.cc/technologies/cyclotron-isotope-production/), [DOTA chelation](https://nuclide.cc/technologies/dota-chelation/), [Hot cells and radiation shielding](https://nuclide.cc/technologies/hot-cells-and-shielding/), [Macropa chelation](https://nuclide.cc/technologies/macropa-chelation/), [Peptide receptor radionuclide therapy (PRRT)](https://nuclide.cc/technologies/prrt/), [Radio-antibody & radio-ADC](https://nuclide.cc/technologies/radioimmunotherapy/), [Radiohybrid (rh) chemistry](https://nuclide.cc/technologies/radiohybrid-chemistry/), [Radiolabelling quality control](https://nuclide.cc/technologies/radiolabelling-quality-control/), [Radiopharmacy and cyclotron networks](https://nuclide.cc/technologies/radiopharmacy-network/), [Targeted alpha therapy](https://nuclide.cc/technologies/targeted-alpha-therapy/), [Therapeutic isotope supply chain (Mo-99, Lu-177, Ac-225)](https://nuclide.cc/technologies/therapy-isotope-supply-chain/)
- ideas: [A global medical isotope supply observatory with forecasts and shortage alerts](https://nuclide.cc/ideas/idea-reg-isotope-supply-observatory/), [A university cyclotron network with shared regulatory files for new tracers](https://nuclide.cc/ideas/idea-fund-academic-radiopharma-pipeline/), [Adding a PARP inhibitor to PSMA radioligand therapy](https://nuclide.cc/ideas/idea-rlt-plus-parp-inhibitor/), [Alpha radioligands after ADC failure](https://nuclide.cc/ideas/idea-alpha-after-adc/), [Alpha-emitting PSMA therapy at first metastatic diagnosis](https://nuclide.cc/ideas/idea-alpha-first-mhspc/), [Alpha-emitting PSMA therapy for oligometastatic (few-lesion) prostate cancer](https://nuclide.cc/ideas/idea-alpha-for-oligometastatic-disease/), [CAIX theranostics: 89Zr-girentuximab PET and 177Lu/225Ac-girentuximab therapy](https://nuclide.cc/ideas/idea-caix-theranostics/), [Fund alpha emitters beyond actinium-225: lead-212, terbium-149 and astatine-211](https://nuclide.cc/ideas/idea-reg-alpha-emitter-portfolio/), [Pretargeted alpha radioimmunotherapy](https://nuclide.cc/ideas/idea-pretargeted-alpha-therapy/), [Recover legacy radium-226 sources worldwide as the feedstock for actinium-225](https://nuclide.cc/ideas/idea-reg-legacy-radium-recovery-ac225/), [Regional cyclotron hubs for actinium-225 with an agreed actinium-227 impurity limit](https://nuclide.cc/ideas/idea-reg-ac225-accelerator-pharmacopoeia/), [Scaling actinium-225 supply with proton accelerators instead of the thorium-229 cow](https://nuclide.cc/ideas/idea-accelerator-ac225-at-scale/)
- isotopes: [Bismuth-213](https://nuclide.cc/isotopes/bi-213/)
- indications: [Metastatic castration-resistant prostate cancer](https://nuclide.cc/indications/prostate-mcrpc/), [Neuroendocrine tumours](https://nuclide.cc/indications/neuroendocrine/), [Prostate cancer](https://nuclide.cc/indications/prostate/)
- targets: [FAP](https://nuclide.cc/targets/fap/), [PSMA](https://nuclide.cc/targets/psma/), [Somatostatin receptor 2](https://nuclide.cc/targets/sstr2/)
- companies: [Actinium Pharmaceuticals](https://nuclide.cc/companies/actinium-pharmaceuticals/), [AdvanCell](https://nuclide.cc/companies/advancell/), [Aktis Oncology](https://nuclide.cc/companies/aktis-oncology/), [Alpha-9 Oncology](https://nuclide.cc/companies/alpha-9-oncology/), [Ariceum Therapeutics](https://nuclide.cc/companies/ariceum-therapeutics/), [AstraZeneca](https://nuclide.cc/companies/astrazeneca/), [Bayer](https://nuclide.cc/companies/bayer/), [Bristol Myers Squibb](https://nuclide.cc/companies/bms/), [BWXT Medical](https://nuclide.cc/companies/bwxt-medical/), [CellBion](https://nuclide.cc/companies/cellbion/), [Convergent Therapeutics](https://nuclide.cc/companies/convergent-therapeutics/), [Eckert & Ziegler](https://nuclide.cc/companies/eckert-ziegler/), [Evergreen Theragnostics](https://nuclide.cc/companies/evergreen-theragnostics/), [Full-Life Technologies](https://nuclide.cc/companies/full-life-technologies/), [Fusion Pharmaceuticals (AstraZeneca)](https://nuclide.cc/companies/fusion-pharma/), [IBA (Ion Beam Applications)](https://nuclide.cc/companies/iba/), [IONETIX](https://nuclide.cc/companies/ionetix/), [ITM Isotope Technologies Munich](https://nuclide.cc/companies/itm/), [Molecular Targeting Technologies](https://nuclide.cc/companies/molecular-targeting-technologies/), [Niowave](https://nuclide.cc/companies/niowave/), [NorthStar Medical Radioisotopes](https://nuclide.cc/companies/northstar-medical-radioisotopes/), [Novartis](https://nuclide.cc/companies/novartis/), [Nusano](https://nuclide.cc/companies/nusano/), [Orano Med](https://nuclide.cc/companies/orano-med/), [Ratio Therapeutics](https://nuclide.cc/companies/ratio-therapeutics/), [RayzeBio (BMS)](https://nuclide.cc/companies/rayzebio/), [SHINE Technologies](https://nuclide.cc/companies/shine-technologies/), [TerraPower Isotopes](https://nuclide.cc/companies/terrapower-isotopes/)
- institutions: [Heidelberg University Hospital / NCT / DKFZ](https://nuclide.cc/institutions/heidelberg-nct/), [Korea Institute of Radiological and Medical Sciences](https://nuclide.cc/institutions/kirams/)
- terms: [Alpha vs beta emitters](https://nuclide.cc/terms/alpha-vs-beta/), [Biological half-life](https://nuclide.cc/terms/biological-half-life/), [Chelator (bifunctional chelating agent)](https://nuclide.cc/terms/chelator-term/), [Half-life](https://nuclide.cc/terms/half-life/), [PRRT (peptide receptor radionuclide therapy)](https://nuclide.cc/terms/prrt-term/), [PSMA-RADS (PSMA reporting and data system)](https://nuclide.cc/terms/psma-rads/), [Radionuclidic purity](https://nuclide.cc/terms/radionuclidic-purity/), [Relative biological effectiveness (RBE)](https://nuclide.cc/terms/relative-biological-effectiveness/), [Theranostics](https://nuclide.cc/terms/theranostics/)
- trials: [ACTION-1](https://nuclide.cc/trials/action-1/), [AlphaBreak (FPI-2265) & AcTION (225Ac-PSMA-617)](https://nuclide.cc/trials/alphabreak/), [ALSYMPCA](https://nuclide.cc/trials/alsympca/), [AZD2265 Compared With Standard of Care in PSMA-positive Metastatic Castration-resistant Prostate Cancer (VECTRA-01)](https://nuclide.cc/trials/nct07611110/), [FPI-2265 (225Ac-PSMA-I&T) and Olaparib for Patients With Metastatic Castration-Resistant Prostate Cancer (mCRPC)](https://nuclide.cc/trials/nct06909825/), [Phase Ib/II Platform Study of Multiple Anti-Cancer Agents in Participants With Metastatic Prostate Cancer](https://nuclide.cc/trials/nct07590934/), [Study Evaluating Dosimetry, Randomized Dose Optimization, Dose Escalation and Efficacy of Ac-225 Rosopatamab Tetraxetan in Participants With PSMA PET-Positive Castration-Resistant Prostate Cancer (CRPC)](https://nuclide.cc/trials/nct06549465/), [Trial of 225Ac-DOTATATE (RYZ101) in Subjects With ER+, HER2-negative Unresectable or Metastatic Breast Cancer Expressing SSTRs.](https://nuclide.cc/trials/nct06590857/)
- pairings: [177Lu-PSMA-617 (Pluvicto) with olaparib](https://nuclide.cc/pairings/pluvicto-plus-olaparib/), [177Lu-PSMA-617 then 225Ac-PSMA rescue therapy](https://nuclide.cc/pairings/beta-psma-then-alpha-psma-rescue/), [Beta PRRT → alpha PRRT](https://nuclide.cc/pairings/prrt-then-alpha-net/), [Beta radioligand → alpha radioligand](https://nuclide.cc/pairings/beta-then-alpha/)
- roadmaps: [Alpha-emitter roadmap: radium-223 → 225Ac-PSMA-617 → a phase 3 pipeline](https://nuclide.cc/roadmaps/alpha-therapy-roadmap/), [Isotope supply roadmap: reactor dependence → non-uranium production → accelerator-made actinium](https://nuclide.cc/roadmaps/isotope-supply-roadmap/), [Neuro-oncology imaging roadmap: FDG PET → amino acid PET → SSTR2 theranostics in meningioma](https://nuclide.cc/roadmaps/neuro-imaging-roadmap/), [PSMA theranostics roadmap: antigen discovery → PSMA PET → 177Lu-PSMA-617 → earlier lines and alpha](https://nuclide.cc/roadmaps/psma-theranostics-roadmap/), [Radiopharmaceutical roadmap: iodine → lutetium → actinium](https://nuclide.cc/roadmaps/radiopharma-roadmap/), [SSTR theranostics roadmap: octreotide scintigraphy → 68Ga-DOTATATE → 177Lu-DOTATATE → alpha](https://nuclide.cc/roadmaps/sstr-theranostics-roadmap/)
- people: [Clemens Kratochwil](https://nuclide.cc/people/clemens-kratochwil/), [Neeta Pandit-Taskar](https://nuclide.cc/people/neeta-pandit-taskar/)
- bottlenecks: [Actinium-225 supply](https://nuclide.cc/bottlenecks/b-ac225-supply/), [Clinical trial capacity for radioligand therapy](https://nuclide.cc/bottlenecks/b-rlt-trial-capacity/), [Dosimetry standardisation for radioligand therapy](https://nuclide.cc/bottlenecks/b-dosimetry-standardisation/), [Manufacturing cost and time for living and radioactive medicines](https://nuclide.cc/bottlenecks/b-manufacturing-cell-therapy/)
- journals: [Journal of Nuclear Medicine](https://nuclide.cc/journals/journal-of-nuclear-medicine/)
- collections: [OpenDose](https://nuclide.cc/collections/opendose/), [US NRC 10 CFR Part 35 (Medical Use of Byproduct Material)](https://nuclide.cc/collections/nrc-regulations-part35/)
- fronts: [Isotope supply](https://nuclide.cc/fronts/f-isotope-supply/), [Targeted alpha therapy](https://nuclide.cc/fronts/f-alpha-therapy/)
- key papers: [225Ac-PSMA-617 for PSMA-targeted alpha-radiation therapy of metastatic castration-resistant prostate cancer](https://nuclide.cc/key-papers/paper-kratochwil-ac225-psma-jnm-2016/), [Phase I dose-escalation study of 225Ac-J591, a PSMA-targeting alpha-emitting antibody, in mCRPC](https://nuclide.cc/key-papers/paper-tagawa-ac225-j591-jco-2024/), [Radiopharmaceutical therapy in cancer: clinical advances and challenges](https://nuclide.cc/key-papers/paper-sgouros-tat-review-nat-rev-2020/)

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JSON: https://nuclide.cc/api/v1/entities/ac-225.json