Radioisotopes in Medicine The Understanding the Atom Series Nuclear energy is playing a vital role in the life of every man, woman, and child in the United States today. In the years ahead it will affect increasingly all the peoples of the earth. It is essential that all Americans gain an understanding of this vital force if they are to discharge thoughtfully their responsibilities as citizens and if they are to realize fully the myriad benefits that nuclear energy offers them. The United States Atomic Energy Commission provides this booklet to help you achieve such understanding. [Illustration: Edward J. Brunenkant] Edward J. Brunenkant, Director Division of Technical Information UNITED STATES ATOMIC ENERGY COMMISSION Dr. Glenn T. Seaborg, Chairman James T. Ramey Wilfrid E. Johnson Dr. Theos J. Thompson Dr. Clarence E. Larson Radioisotopes in Medicine by Earl W. Phelan CONTENTS INTRODUCTION 1 History 1 What Is Radiation? 5 What Is Radioactivity? 5 What Are Radioisotopes? 6 How Are Radioisotopes Used? 7 What Do We Mean by Tracer Atoms? 9 DIAGNOSIS 11 Pinpointing Disease 11 Arsenic-74 14 Chromium-51 15 Cobalt-60 16 Iodine-131 18 Iron-59 23 Phosphorus-32 24 Sodium-24 25 Technetium-99^{_m_} 26 Thulium-170 and Gamma Radiography 27 Tritium 28 Activation Analysis 30 Summary 30 THERAPY 31 A Successful Case 31 General Principles 32 Iodine-131 and Iodine-132 32