This book provides an in-depth account of all aspects of radioembolization, a relatively novel technique based on the efficacy of radiotherapy for the treatment of liver tumors. In the past, the therapeutic radiation dose needed to treat a tumoral area has been sufficiently high to produce permanent damage to the nontumoral liver parenchyma. Radioembolization attempts to overcome this problem by combining embolization (intravascular deployment of particles) and brachytherapy (local administration of radiotherapy with the aid of a device, namely the particles themselves). The technique is based on improvements in percutaneous endovascular procedures which have allowed the deployment of small (25-35 µm) microspheres loaded with yttrium-90 that deliver high doses of beta-radiation specifically to the tumoral area. Performance of the procedure demands close familiarity with the hepatic vascular anatomy in order to ensure avoidance of vessels going to other territories. Furthermore, detailed knowledge of liver function, tumor volume, and liver vascular shunting is needed in order to calculate the appropriate therapeutic dose in each particular case. All of these topics are addressed in depth in this book, and initial clinical results are presented, showing that constant local control can be achieved with a reasonably low rate of complications. These promising results may lead to a progressive change in the therapeutic indication for radioembolization, and in some cases it could even become the therapy of choice.