Information for Physicians

About Selective Internal Radiation Therapy

Selective Internal Radiation Therapy or SIRT consists of delivering SIR-Spheres Y-90 resin microspheres (yttrium-90 labelled microspheres) into the hepatic arterial supply of the liver following which the SIR-Spheres Y-90 resin microspheres lodge preferentially in the pre-capillary vasculature of the hepatic tumours. The microspheres deliver high doses of ionising pure beta radiation to the tumour, while maintaining the radiation dose to the normal liver at a tolerable level.

SIR-Spheres Y-90 resin microspheres consist of biocompatible microspheres containing yttrium-90 with a size between 20 and 60 microns in diameter. Yttrium-90 is a high-energy pure 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. In use requiring the isotope to decay to infinity, 94% of the radiation is delivered in 11 days leaving only background radiation with no therapeutic value. SIR-Spheres Y-90 resin microspheres are a permanent implant.

About SIR-Spheres microspheres

Intrinsic to the concept of SIRT is the preferential placement of the radioactive microspheres selectively into tumours rather than healthy liver tissue. This concept exploits the blood supply to hepatic tumours, which is derived largely from the hepatic artery as opposed to healthy liver tissue which derives the vast majority of its blood supply from the portal vein. By delivering the microspheres into the hepatic artery, they are selectively delivered to tumours whereupon they lodge in the microvasculature of the tumour. This technique allows numerous and/or small tumours to be treated and can be used in patients who are not candidates for surgical resection.

Placement of the microspheres into the hepatic artery is therefore fundamental for this treatment modality. By virtue of the complexity of SIRT treatment, it is essential that close collaboration exists in a multidisciplinary team consisting at least of a medical oncologist, a nuclear medicine physician, an interventional radiologist and an oncologic surgeon.

The Work-up Procedure

Selective Internal Radiation Therapy is typically a process comprising an initial work-up procedure which is then followed by the SIR-Spheres Y-90 resin microspheres implantation procedure approximately a week later. In the work-up procedure, the interventional radiologist uses a trans-femoral catheter to access the hepatic arterial vasculature, map the unique vascular anatomy and identify the vessels feeding the tumour. Extra-hepatic vessels branching off the hepatic artery (gastro-duodenal artery, right gastric artery etc.) will typically be prophylactically occluded in order to prevent the deposition of SIR-Spheres Y-90 resin microspheres outside the liver. Subsequently, technetium-99m labelled macroaggregated albumin (99mTc-MAA) is injected into the hepatic artery. These macroaggregated albumin particles are approximately the same size as SIR-Spheres Y-90 resin microspheres so that they can be used to identify potential incorrect positioning of the SIR-Spheres Y-90 resin microspheres by means of a gamma camera. The 99mTc-MAA nuclear medicine scan is also used to determine the presence of shunting to the lungs.

The implantation procedure

In the SIR-Spheres Y-90 resin microspheres implantation procedure, the SIR-Spheres Y-90 resin microspheres are administered by injection through a trans-femoral catheter into the hepatic artery. As there are frequent arterial anomalies in the blood supply to the liver, the interventional radiologist must be familiar with the anomalies. All areas of tumour within the liver are to be targeted with SIR-Spheres Y-90 resin microspheres and this usually involves treating both lobes of the liver. However, it is essential that the SIR-Spheres Y-90 resin microspheres are not delivered to other organs such as the duodenum, stomach, pancreas or other visceral organs.

If the liver tumours are limited to only one hepatic lobe, then the interventional radiologist may place the catheter selectively into the lobar artery supplying only the tumour bearing hepatic lobe. The SIR-Spheres Y-90 resin microspheres will then be delivered only to the tumour bearing hepatic lobe thus sparing the other normal hepatic lobe. This is an excellent way of delivering high doses of radiation to tumours while minimising the chance of damaging the normal liver tissue. In the FOXFIRE Global study, any method of injection, (i.e. whole liver, lobar by lobar, selective or super selective administrations) is allowed if performed within the same session.

The implantation procedure

After completing of the SIR-Spheres Y-90 resin microspheres implantation procedure a nuclear medicine Bremsstrahlung scan may be performed as a quality assurance step in order to confirm the placement of the SIR-Spheres Y-90 resin microspheres within the intended location in the liver.


The following schedule summarises the complete planning and SIRT procedure:

The complete planning and SIRT procedure

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Multi-Centre Randomised Controlled Study

FOXFIRE Global is a multi-centre randomised controlled study that will assess the effect of adding targeted radiation, in the form of SIR-Spheres Y-90 resin microspheres, to a standard chemotherapy regimen of FOLFOX6m as first line therapy in patients with non-resectable liver metastases from primary colorectal adenocarcinoma. Patients may, at the investigator's discretion, receive the biologic agent bevacizumab as part of the chemotherapy regimen. More than 200 patients were recruited in the study.