1 hours. The maximum range of emissions in tissue is 11mm with a mean of 2. 5mm. In therapeutic use, requiring the isotope to decay to infinity, 94% of the radiation is delivered in 11 days. SIR-Spheres Y-90 resin microspheres distribute non-uniformly in the liver due to the physiology of hepatic arterial flow, the tumour to normal liver ratio of the tissue vascularity and tumour size. The rim of the tumour gets higher density per unit distribution of SIR-Spheres Y-90 resin microspheres than the normal liver.