# Holmium-166 microspheres

Source: https://nuclide.cc/drugs/ho-166-microspheres/  
Nuclide record `ho-166-microspheres` (Agent). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

Tiny plastic beads carrying a radioactive, slightly magnetic metal are injected into the artery feeding a liver tumour. Because the metal shows up on both nuclear scans and MRI, doctors can check exactly where the beads went.

## Summary

QuiremSpheres are holmium-166-labelled poly-L-lactic acid microspheres for radioembolisation (SIRT) of unresectable liver tumours, developed at University Medical Center Utrecht and commercialised by Quirem Medical (later acquired by Terumo). Holmium-166 has a physical half-life of 26.8 hours, so more than 90% of the radiation dose is delivered within the first four days after administration.

The product received CE marking as an active implantable medical device in April 2015, and a matching low-activity test dose (QuiremScout, identical size and shape) was CE-marked in 2018-2019 to predict lung shunting and biodistribution before therapy. Holmium-166 emits both beta particles (for therapy) and a gamma photon, and is paramagnetic, which allows quantitative SPECT and MRI-based dosimetry after treatment, alongside the more usual post-treatment imaging used for yttrium-90 products.

QuiremSpheres has not obtained FDA approval and is used in Europe and other CE-mark-recognising markets; NICE (UK) technology appraisal TA985 reviewed its use in advanced HCC. It is one of three commercially available liver radioembolisation microsphere products, alongside the yttrium-90 resin (SIR-Spheres) and glass (TheraSphere) microspheres.

## Fields

- Kind: Agent
- Status: approved
- Last checked: 2026-09-22
- Also known as: QuiremSpheres; 166Ho-PLLA microspheres
- Tags: radioembolisation; liver; beta emitter; CE mark
- Brand: QuiremSpheres
- Modality: radioembolisation
- Mechanism: Poly-L-lactic acid (PLLA) microspheres loaded with holmium-166 (a beta emitter that also emits an imageable gamma photon and is paramagnetic, so uptake can be checked on SPECT or MRI as well as CT), infused through a hepatic artery catheter to treat unresectable liver tumours.
- Approvals: EU 2015: Treatment of unresectable liver tumours (radioembolisation)
- Dosing: Intra-arterial infusion into the hepatic artery via catheter; Single administration, typically with a QuiremScout test dose beforehand for dosimetry

## Sources

- Holmium-166 radioembolisation: current status and future perspectives, PMC 2022: https://pmc.ncbi.nlm.nih.gov/articles/PMC9626412/
- NICE TA985: QuiremSpheres for advanced HCC: https://www.nice.org.uk/guidance/ta985/chapter/2-Information-about-QuiremSpheres
- Terumo: QuiremScout CE mark announcement, 2019: https://www.terumo.com/newsrelease/detail/20190107/234

## Connected records

- drugs: [Yttrium-90 glass microspheres](https://nuclide.cc/drugs/y-90-glass-microspheres/), [Yttrium-90 resin microspheres](https://nuclide.cc/drugs/y-90-resin-microspheres/)
- isotopes: [Holmium-166](https://nuclide.cc/isotopes/ho-166/), [Yttrium-90](https://nuclide.cc/isotopes/y-90/)
- indications: [Hepatocellular carcinoma](https://nuclide.cc/indications/hcc/)
- technologies: [Radioembolisation (TARE / SIRT, yttrium-90)](https://nuclide.cc/technologies/radioembolisation-tare/)

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