Aim: Selective Internal Radiation Therapy (SIRT), also known as radioembolization, is a liver-directed therapy for inoperable primary and secondary liver tumours. The aim of this study is to review the Standard Operating Procedure (SOP) used in the Radiopharmacy Department of the Oxford University Hospital NHS Foundation Trust to prepare 90Y labelled SIR-Spheres microspheres, in order to improve the dispensing procedure for delivering the intended patient treatment doses. The specification is: the activity prescribed ±10%. Methods: Eleven tests were carried out according to the current SOP. Radioactivity was diluted in up to 3 or 5 ml of water for injection and inserted into a V-vial. Following this, the used syringes and needles were measured using a Capintec Radionuclide Calibrator to check for any remaining activity. Results: One of the doses dispensed (11th) was below the specification. This, is in, turn triggered the review of the SOP. The operator must dilute the dose up to 3 ml with water for injection and inject it in the V-vial. According to the new procedure, using the same syringe and needle the operator must draw up an additional 1 ml of water for injection and inject this volume again into the V-vial. This washes the syringe and needle and removes any remaining activity. Conclusions: The reviewed SOP to prepare 90Y labelled SIR-spheres microspheres has shown to improve the dispensing procedure in terms of dose delivered to the patient. The collected data has been accepted and the reviewed SOP implemented in the Radiopharmacy Department at Oxford University Hospitals NHS Foundation Trust.