This book offers a comprehensive, practical guide to understanding the physical and biological characteristics of proton beam radiotherapy. The application of proton beams to the treatment of solid cancers has expanded exponentially over the last decade due to their physical properties, which make it possible to administer higher doses of radiation to lesions with only a minimum dose to the surrounding healthy tissues. Accordingly, understanding the basic aspects of proton beam radiotherapy is a primary concern not only for medical physicists and radiation biologists, but also for all physicians involved in cancer treatment using proton beams. The major aspects discussed include the technique¿s development background, the