Primary standardization of SIR-Spheres based on the dissolution of the 90 Y-labeled resin microspheres

The project "Metrology for molecular radiotherapy" is a collaborative European project initiated to bring together expertize in ionizing radiation metrology and nuclear medicine research. This project deals with the development of personalized dosimetry to individual patients who are undergoing molecular radiotherapy (also known as targeted radionuclide therapy). The general aim is to provide a metrological traceability to primary standards for individual dosimetry in the case of molecular radiotherapy. In particular, one objective is the standardization of Y-90-labeled resin microspheres SIR-Spheres (Sirtex, Sydney, Australia) used for the treatment of liver cancer by radioembolization. The present paper describes the primary measurements carried out using the Triple to Double Coincidence Ratio (TDCR) method applied after the complete dissolution of the SIR-Spheres in the Sirtex vial. A method for the dissolution was developed to optimize the homogeneity of the solution to enable the primary measurements based on Cherenkov and liquid scintillation counting. A comprehensive description of the protocol implemented for the microsphere dissolution is reported. First calibration factors obtained with the reference ionization chambers at LNE-LNHB are also given.