This book comprehensively covers radiation detectors and their methods in medicine. An important and expanding topic, this text combines all radiation detector information into one single volume. The text is divided into five sections. The first introduces the topic and its history alongside the measuring devices used. The second section covers external beam, including absolute dosimetry, small field, and MR-Linac. The third section extensively covers brachytherapy. The fourth section covers diagnostic radiation detection, including diagnostic dosimetry, CT detectors, and nuclear medicine detectors. Finally, authors cover other detectors, like flash therapy, and explore the future of the field. This is an ideal guide for radiation oncologists and medical physicists.