⁹⁰Sr content in ⁹⁰Y-labeled SIR-Spheres and Zevalin

Three different ⁹⁰Y internally-administered radionuclide therapies are currently used in both standard-of-care and clinical trial procedures at MD Anderson Cancer Center. TheraSphere and SIR-Spheres therapies utilize ⁹⁰Y-labeled microspheres, while Zevalin is an ⁹⁰Y-labeled radioimmunotherapeutic agent. Several publications have indicated radionuclidic impurities resulting from ⁹⁰Y production methods. The ⁹⁰Y in SIR-Spheres and Zevalin are produced from a ⁹⁰Sr/⁹⁰Y generator, which leaves measurable quantities of ⁹⁰Sr in the final product. TheraSphere ⁹⁰Yis produced in a nuclear reactor which results in a large number of impurities, most notably ⁸⁸Y and ⁹¹Y. Product information sheets reference these impurities with specific limits given. These limits represent a tiny fraction of the total product activity, and in the case of TheraSphere and SIR-Spheres gammaemitting impurities, this has been verified in the literature. An analysis of ⁹⁰Sr impurities in SIR-Spheres and Zevalin is presented in this paper. Impurity quantities were found to be within the vendors' documented limits.