Radiation therapy or radiotherapy is a cancer therapy using ionizing radiation that is aimed at killing or controlling malignant cells of a tumor. It may be curative if the cancer is localized to one part of the body. It can also be used as a part of adjuvant therapy in order to prevent tumor recurrences after surgery, along with other systemic therapies such as chemotherapy, hormone therapy and immunotherapy. Ionizing radiation acts against the cancer by damaging the DNA of cancerous tissue therefore resulting in cellular death. The primary types of radiation therapy are external beam radiation therapy, intraoperative radiotherapy, brachytherapy, contact X-ray brachytherapy, etc. Radiotherapy may be used as a palliative treatment or as a therapeutic treatment. The topics covered in this extensive book deal with the core aspects of radiation oncology. From theories to research to practical applications, case studies related to all contemporary topics of relevance to this field have been included in this book. Scientists and students actively engaged in radiation oncology will find this book full of crucial and unexplored concepts.