Technical note:: The calibration of 90Y-labeled SIR-Spheres® using a nondestructive spectroscopic assay

90Y-labeled SIR-Spheres (R) are currently used to treat patients with hepatic metastases secondary to colorectal adenocarcinoma. In general, the prescribed activity is based on empirical data collected during clinical trials. The activity of the source vial is labeled by the manufacturer as 3.0 GBq +/- 10% and is not independently verified by the end user. This technical note shows that the results of a nondestructive spectroscopic assay of a SIR-Spheres (R) sample was 26% higher than the activity stated by the manufacturer. This difference should not impact the current empirical prescription method but may be problematic for patient-specific dosimetry applications, such as image-based dosimetry. (C) 2008 American Association of Physicists in Medicine.