The main purpose of this study is to determine the safety and toxicity of treatment with SIR-Spheres® in patients with unresectable primary liver cancer or hepatocellular carcinoma (HCC). Other purposes of this study include assessment of the effect of treatment on overall survival, the length of time it takes for the disease to worsen, if and how the treatment affects the patient's quality of life, and if and how the cancer responds to the treatment.