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What are SIR-Spheres microspheres

img-sirt6SIR-Spheres microspheres are a medical device used in Selective Internal Radiation Therapy (SIRT) for liver tumours. SIR-Spheres microspheres are a permanent implant and for single use only. The biocompatible resin microspheres containing yttrium-90 have a median diameter of 32.5 microns (range between 20 and 60 microns).

Yttrium-90 is a high-energy beta-emitting isotope with no primary gamma emission. The maximum energy of the beta particles is 2.27MeV with a mean of 0.93MeV. The maximum range of emissions in tissue is 11mm with a mean of 2.5mm. The half-life is 64.1 hours. Following administration, 94% of the radiation is delivered in 11 days.

These properties of the SIR-Spheres microspheres mean that the microspheres lodge preferentially in the microvasculature surrounding the tumour, maximising tumourcidal effects and minimising the effects on healthy liver parenchyma (Also see Mode of Action and Radiation Safety Aspects).

What is Selective Internal Radiation Therapy

Selective Internal Radiation Therapy (SIRT), also known as Radioembolisation, is a liver-directed therapy for inoperable liver tumours. SIRT is administered by a specially trained Interventional Radiologist.
A microcatheter is used to deliver millions of radioactive microspheres into the hepatic artery, where they are carried into the arterioles and selectively lodge in the tumour microvasculature (for further information see Mode of Action).


Treatment Goals

-Increase the time to progression
-Extend overall survival
-Potentially downsize or downstage tumours for liver resection, ablation, or transplantation
-Provide palliation of symptoms

SIRT can be combined with modern chemotherapy or administered as a monotherapy, either during a chemotherapy holiday, in a salvage setting or as an alternative to local chemotherapy.

Radiotherapy, together with chemotherapy and surgery, is a major pillar in the treatment of cancer. However, the utility of external beam radiation in the management of liver tumours is limited by the sensitivity of the uninvolved liver parenchyma to radiation. Selective Internal Radiation Therapy with SIR-Spheres microspheres offers patients an opportunity to access radiotherapy for inoperable primary and secondary liver tumours whilst sparing normal liver parenchyma.