The use of high-energy radiation to damage cancer cells' DNA and destroy their ability to divide and grow is referred to as radiation oncology. It can be administered using external beam radiation therapy or brachytherapy to treat cancer. External beam radiation therapy can be generated by a linear accelerator, which accelerates electrons to produce x-rays or gamma rays. Another form of external beam radiation therapy that uses cyclotrons or synchrotrons to produce charged atoms that destroy tumors is known as proton therapy. In branchytherapy, radioactive sources are sealed in needles, seeds, wires, or catheters, and implanted directly into or near a tumor on a temporary or permanent basis. There are several types of radiation therapy techniques such as intensity-modulated radiation therapy, stereotactic radiosurgery, gamma knife, stereotactic body radiation therapy, image-guided radiation therapy, and radioembolization. This book brings forth some of the most innovative concepts and elucidates the unexplored aspects of radiation therapy. The ever growing need of advanced technology is the reason that has fueled the research in the field of radiation oncology in recent times. This book will serve as a reference to a broad spectrum of readers.