This animated Mode of Action video has been created by Sirtex Medical to serve as an educational resource that provides a narrative look at Selective Internal Radiation Therapy (SIRT) using SIR-Spheres® Y-90 resin microspheres. SIRT using SIR-Spheres microspheres is a targeted liver tumor treatment that delivers millions of radioactive microspheres directly to inoperable liver tumors. SIR-Spheres Y-90 resin microspheres are the only fully FDA-approved microsphere radiation therapy for the treatment of colorectal liver metastases. This video covers explanation and animation of the SIR-Spheres® Y-90 resin microspheres procedure.