Development of activity standard for 90Y microspheres

Abstract

90Y is a therapeutic radiopharmaceuticals used in the treatment of liver cancer following implantation via a catheter in the hepatic artery, 90Y microspheres are embolised in the microvasculature of liver cancer where they irradiate the tumour by a process known as selective internal radiation therapy. SIR-spheres are radiopharmaceutical products that are comprised of 90Y microspheres suspended in sterile, pyrogen-free water for injection into patients. It is necessary to establish for the SIR-spheres production the capability of accurately measuring the activity of this product to a traceable national measurement standard. In the SIR-spheres product, the microspheres are non-biodegradable plastic beads, which have a density of 1.0 g/ml and a diameter of approximately 35 mm. 90Y used was the nuclear reactor-produced radionuclide. The concentration of the microspheres is approximately 40% and patient doses of SIR- product are usually prepared in a Wheaton vial by ARI with an activity of 3 GBq in a volume of 5 ml. The direct standard transfer is limited to a small quantity of SIR-spheres of about 1ml due to the difficulty of effectively digesting a large quantity of SIR-spheres such as 5 ml. The calibration factor for 5ml SIR-spheres may be derived from the factor for 1ml SIR-spheres, although relatively large uncertainty may be introduced due to the inhomogeneity of activity concentration dispensed into 1 and 5ml samples.