Image-guided 3D Conformal or Intensity Modu- by the various classifcation systems, which might lated Radiation Terapy aims to deliver high doses be hard to fnd in scans performed without contrast of radiation to the tumor, while trying to maintain medium. dose levels to healthy tissue within tolerable limits. Together with experienced radiologists for each Terefore, it is of key importance to defne the dif- anatomical region, we have developed a set of st- ferent target volumes, gross tumor volume (GTV), dards for the acquisition of planning CT images, clinical target volume (CTV), planning target vol- standardizing the parameters for scan performance ume (PTV), and organs at risk (OARs), on the basis and those concerning patient positioning and - of in-depth knowledge of the human anatomy, of mobilization. anatomicoradiological aspects, and of anatomical In the second section of the book we describe the and geometric variations during the radiation plan- role and importance of radiological imaging in ta- ning and treatment. get defnition, including lymph nodes, especially for We have prepared this guide to meet the needs image-guided radiation therapy (IGRT).