Selective internal radiation therapy (SIRT) has become a term used to define the application of a therapeutic radionuclide into the liver to treat either primary or secondary liver tumors.1 However, the original meaning was much wider and included the treatment of brain tumors2 though this has not proved as popular as its use within the liver. This is because of the dual arterial supply to the liver with hepatocytes being supplied by the hepatic artery and portal vein (despite its name it is an artery) but both primary hepatocellular cancer (HCC) and secondaries to the liver being supplied by only the hepatic artery.1 The first methods in the 1980s used an iodized poppyseed oil, Lipiodol, this was labelled in a stable fashion by a group from France and used in the treatment of HCC in France and the UK.3,4 In direct comparative trials it was found to be as effective as trans-arterial chemo-embolization (TACE) but less toxic with shorter hospital stays.4 This treatment required close co-operation between interventional radiology and nuclear medicine to deliver the required activity of radioactive produce selectively to the correct hepatic artery or more selectively to a branch of that artery. This co-operation remains the key to the success of SIRT.1 The method was also found useful in improving survival in patients with a fully or partially blocked portal vein a common occurrence in patients with HCC.5

The chemistry involved in the preparation of this method was complex and handling of the I-131 Lipiodol was not without risks this lead in the late 1990s to a project from the International Atomic Energy Agency to look at the use of Re-188 Lipiodol in HCC.6,7 However, this method was not found to be of use in metastatic cancers in the liver which is more common in Europe and North America than HCC. This led in the 1990s to the development and early clinical trials of 2 Yttrium-90 (Y-90) labelled products. One of these used Y-89 encased glass beads which when neutron bombarded to Y-90 would produce a product which could give via infusion into the relevant hepatic artery or branch of a hepatic artery.8 A second group in Australia used Y-90 impregnated resin spheres similar to those used in trans-arterial embolization to achieve similar results.9 These 2 products began to be used more widely across the world in the 2000s and 2010s so the science and clinical experience of SIRT increased. These Y-90 particulates when administered via the hepatic arteries would become trapped in the fine angiogenic blood vessels which surround the tumor.8,9