CERN‑MEDICIS: Pioneering radionuclides for precision medicine

CERN’s MEDICIS facility is contributing to the advancement of nuclear medicine by producing unconventional radionuclides for diagnosis and targeted therapy against tumours and other diseases. Radionuclides – atoms with either an excess or deficiency of neutrons – play an essential role in medical imaging and in delivering highly localised radiation to eliminate malignant cells while sparing healthy tissue. By enabling the development of radionuclides with improved physical and chemical properties, MEDICIS supports the growing field of precision medicine and theranostics: the combined practice of diagnosis and therapy.

MEDICIS operates in synergy with CERN’s ISOLDE facility. MEDICIS places a second target behind the primary ISOLDE target, taking advantage of the beam‑induced reaction products. The irradiated target releases atoms that diffuse out, are ionised in a specialised ion source, and then undergo high‑resolution mass separation. These radionuclides are dispatched to hospitals and research institutes across Europe. Once delivered, researchers chemically process and attach them to biomolecules such as peptides, sugars, or proteins allowing them to be used to selectively target tumour tissue or specific organs.

Since full operation in 2018, MEDICIS has produced Actinium‑225 (Ac-225), a key radionuclide for targeted alpha therapy (TAT); Samarium‑153 in highly concentrated form, used in cleaner and more effective cancer treatments; and Thulium/Erbium‑165, relevant for advanced molecular imaging and therapeutic research. MEDICIS’ mass‑separation capabilities are particularly important for radionuclides like Ac‑225, where conventional chemical purification cannot eliminate contaminants such as Actinium‑227 (Ac‑227) – making them less pure and useful for medical applications.

Targeted alpha therapy (TAT) exemplifies the impact of mass‑separated, high‑purity isotopes. Alpha particles deposit large amounts of energy over extremely narrow distances, offering the possibility of destroying cancer cells with minimal collateral damage. Accelerator‑based production coupled with isotope‑selective mass separation, as developed at MEDICIS, offers a scalable path to medical‑grade Ac‑225 while suppressing long‑lived Ac‑227 impurities that cannot be removed chemically.

In 2025, MEDICIS was granted approval by the CERN Council to supply mass‑separated radionuclides for clinical treatment. Test deliveries were made to Heidelberg University Hospital at the end of 2025 to provide feedback on the best supply conditions required for the clinical trial. This milestone anchors a concrete clinical pathway for radionuclides such as High Specific Activity Samarium‑153 and other next‑generation theranostic radionuclides, including Ac‑225, Radium‑224, and Erbium‑165, either used as diagnostics, therapeutics, or both.

In the last quarter of 2025, for the first time MEDICIS shipped Ac-225 radionuclides to a private company, Rayzebio, the only pharmaceutical company at that time in phase three clinical trials with Ac-225 – the final phase before reaching marketing authorisation. Rayzebio undertook conformity testing of MEDICIS’ Ac-225 to verify its potential suitability for use in clinical settings.

MEDICIS also played a central role in the EU-funded project PRISMAP, bringing together leading institutes to provide coordinated access to high‑quality radionuclides for life and medical sciences. Through PRISMAP, MEDICIS coordinates with European institutes to provide access to non‑conventional radionuclides and to develop shared standards for their application for research and handling as pharmaceutical products. In parallel, clinical partnerships are expanding the facility’s translational impact to transfer the supply of mass‑separated radionuclides into clinical research settings.

PRISMAP is significantly advancing nuclear‑based cancer research by improving access to high‑purity radionuclides across Europe. Over five years, the project has supported 47 research projects in 19 countries and delivered 159 batches of 23 radionuclides, helping scientists develop new diagnostic and therapeutic tools.

CERN‑MEDICIS plays a key role as the only facility worldwide producing radionuclides via mass separation dedicated to biomedical research, and the “PRISMAP project was instrumental in developing this innovative theranostic approach. By connecting eight radionuclide production facilities and five biomedical research centres across Europe, the project has undoubtedly stimulated research into cancer treatment”, said Thierry Stora, Head of the CERN-MEDICIS facility and PRISMAP coordinator.

PRISMAP ended in 2025, and the consortium proposed a follow-up project: PRISMAPplus was recently selected for funding by the European Commission, a tangible sign of the success of its predecessor.

CERN technical contacts: Charlotte Duchemin, Edgars Mamis, and Thiery Stora.