The classic with a modern touch! Since the publication of the first edition of this clinical treatise in 1998, the field of radiation oncology has seen changes in all modalities, most notably, in the treatment planning and delivery subprocesses. Beginning with the advent of intensity modulated radiation therapy (IMRT) which revolutionized the field, there have been important developments in image-guided radiotherapy (IGRT), volumetric modulated arc therapy (VMAT), stereotactic body radiotherapy (SBRT), and proton therapy. The book captures the essence of these technologies from a practitioner's viewpoint. The latest edition comes only five short years after the last one, but is timely, considering the rapid advances in radiation oncology. The book's main focus is treatment planning and it presents this area brilliantly from perspectives of physics, biology, and clinical practice. Important treatment planning-related topics in these areas have been highlighted for the reader. However, like the previous editions, the book's main focus remains unchanged: improved patient care through effective and efficient use of new technologies. The book's intended audience is the radiation oncology team: radiation oncologists, medical physicists, and dosimetrists. The inclusion of Key Points (chapter summary) and Study Questions at the end of each chapter should appeal to residents preparing for their board examination. The fourth edition of the book has been completely updated and is accompanied by an e-book with enhanced navigation tools including fully searchable text. All chapters have been revised and most re-written by new authors chosen for their expertise in the field. The new edition also includes an expanded coverage of proton therapy and SBRT. Owing to its increasing and somewhat controversial use, there is also a chapter devoted to comparing the role of protons versus photons in radiation oncology. The book is divided into two sections. Section 1 consists of 23 chapters addressing the physics and biology of treatment planning. This section provides a systematic and logical refresher on pertinent topics, starting with patient imaging, treatment simulation, and a discussion of treatment planning algorithms used for photons, protons, electrons, and brachytherapy. This is followed by a chapter on quality assurance and commissioning of treatment planning systems. The second half of this section is devoted to technical and radiobiological considerations related to various treatment modalities. Section 1 concludes with an important chapter on treatment plan evaluation. Section 2 has 11 chapters devoted to treatment planning for site specific cancers presented from a clinical perspective. The book is clearly written and easy to read—a hallmark of all books penned by Dr. Khan. It provides a ready resource for finding answers to treatment planning related questions in radiation oncology. Perhaps, owing to size limitations, some topics are not covered in detail; however, ample references are provided for the interested reader. It is my hope that the book's future edition will include an expanded list of Study Questions. It is also hoped that the next edition will cover topics related to the evolving, yet important, field of MR-based treatment planning and delivery. In summary, the book is a joy to read and should appeal to all readers interested in radiation oncology. Anil Sethi is an Associate Professor in Radiation Oncology at Loyola University Health System, Chicago, IL. He is board certified by the American Board of Medical Physics (ABMP) and the American Board of Radiology (ABR). He is teaching medical physics to residents and clinical physicists and his research interests are in IMRT, IGRT, and all special procedures in RT especially SRS and SBRT.