Radioisotopes in Medicine

Part 1

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.

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 Boron-10 33 Phosphorus-32 35 Gold-198 37 Beads, Needles, and Applicators 38 Teletherapy 41 CONCLUSIONS 43 APPENDIX 44 SUGGESTED REFERENCES 47

United States Atomic Energy Commission Division of Technical Information Library of Congress Catalog Card Number: 66-62749 1966

This multi-detector positron scanner is used to locate tumors. A radioisotope-labeled substance is injected into the body and subsequently concentrates in the tumor tissue. The radioisotope emits positrons that immediately decay and produce two gamma rays that travel in opposite directions. These rays are detected simultaneously on a pair of opposing detection crystals and a line is established along which the tumor is located. This method is one of many ways doctors use radioisotopes to combat disease. In this, as in many other procedures described in this booklet, the patient remains comfortable at all times.]

Earl W. Phelan is Professor of Chemistry at Tusculum College, Greeneville, Tennessee. From 1952 to 1965, he served as Staff Assistant in the Laboratory Director’s Office at Argonne National Laboratory, where his duties included editing the Argonne Reviews and supplying information to students. For 22 years prior to moving to Argonne he served as Head of the Chemistry Department of the Valdosta State College In Georgia. He received his B.S. and Ph.D. degrees from Cornell University.]

Radioisotopes in Medicine

By EARL W. PHELAN

INTRODUCTION

History

The history of the use of radioisotopes for medical purposes is filled with names of Nobel Prize winners. It is inspiring to read how great minds attacked puzzling phenomena, worked out the theoretical and practical implications of what they observed, and were rewarded by the highest honor in science.

For example, in 1895 a German physicist, Wilhelm Konrad Roentgen, noticed that certain crystals became luminescent when they were in the vicinity of a highly evacuated electric-discharge tube. Objects placed between the tube and the crystals screened out some of the invisible radiation that caused this effect, and he observed that the greater the density of the object so placed, the greater the screening effect. He called this new radiation X rays, because x was the standard algebraic symbol for an unknown quantity. His discovery won him the first Nobel Prize in physics in 1901.

A French physicist, Antoine Henri Becquerel, newly appointed to the chair of physics at the Ecole Polytechnique in Paris, saw that this discovery opened up a new field for research and set to work on some of its ramifications. One of the evident features of the production of X rays was the fact that while they were being created, the glass of the vacuum tube gave off a greenish phosphorescent glow. This suggested to several physicists that substances which become phosphorescent upon exposure to visible light might give off X rays along with the phosphorescence.

Becquerel experimented with this by exposing various crystals to sunlight and then placing each of them on a black paper envelope enclosing an unexposed photographic plate. If any X rays were thus produced, he reasoned, they would penetrate the wrapping and create a developable spot of exposure on the plate. To his delight, he indeed observed just this effect when he used a phosphorescent material, uranium potassium sulfate. Then he made a confusing discovery. For several days there was no sunshine, so he could not expose the phosphorescent material. For no particular reason (other than that there was nothing else to do) Becquerel developed a plate that had been in contact with uranium material in a dark drawer, even though there had been no phosphorescence. The telltale black spot marking the position of the mineral nevertheless appeared on the developed plate! His conclusion was that uranium in its normal state gave off X rays or something similar.

At this point, Pierre Curie, a friend of Becquerel and also a professor of physics in Paris, suggested to one of his graduate students, his young bride, Marie, that she study this new phenomenon. She found that both uranium and thorium possessed this property of radioactivity, but also, surprisingly, that some uranium minerals were more radioactive than uranium itself. Through a tedious series of chemical separations, she obtained from pitchblende (a uranium ore) small amounts of two new elements, polonium and radium, and showed that they possessed far greater radioactivity than uranium itself. For this work Becquerel and the two Curies were jointly awarded the Nobel Prize in physics in 1903.

At the outset, Roentgen had noticed that although X rays passed through human tissue without causing any immediate sensation, they definitely affected the skin and underlying cells. Soon after exposure, it was evident that X rays could cause redness of the skin, blistering, and even ulceration, either in single doses or in repeated smaller doses. In spite of the hazards involved, early experimenters determined that X rays could destroy cancer tissues more rapidly than they affected healthy organs, so a basis was established quite soon for one of Medicine’s few methods of curing or at least restraining cancer.

The work of the Curies in turn stimulated many studies of the effect of radioactivity. It was not long before experimenters learned that naturally radioactive elements—like radium—were also useful in cancer therapy. These elements emitted gamma rays, which are like X rays but usually are even more penetrating, and their application often could be controlled better than X rays. Slowly, over the years, reliable methods were developed for treatment with these radioactive sources, and instruments were designed for measuring the quantity of radiation received by the patient.

The next momentous advance was made by Frederic Joliot, a French chemist who married Irene Curie, daughter of Pierre and Marie Curie. He discovered in 1934 that when aluminum was bombarded with alpha particles from a radioactive source, emission of positrons (positive electrons) was induced. Moreover, the emission continued long after the alpha source was removed. This was the first example of artificially induced radioactivity, and it stimulated a new flood of discoveries. Frederic and Irene Joliot-Curie won the Nobel Prize in chemistry in 1935 for this work.

Others who followed this discovery with the development of additional ways to create artificial radioactivity were two Americans, H. Richard Crane and C. C. Lauritsen, the British scientists, John Cockcroft and E. T. S. Walton, and an American, Robert J. Van de Graaff. Ernest O. Lawrence, an American physicist, invented the cyclotron (or “atom smasher”), a powerful source of high-energy particles that induced radioactivity in whatever target materials they impinged upon. Enrico Fermi, an Italian physicist, seized upon the idea of using the newly discovered neutron (an electrically neutral particle) and showed that bombardment with neutrons also could induce radioactivity in a target substance. Cockcroft and Walton, Lawrence, and Fermi all won Nobel Prizes for their work.

Patient application of these new sources of bombarding particles resulted in the creation of small quantities of hundreds of radioactive isotopic species, each with distinctive characteristics. In turn, as we shall see, many ways to use radioisotopes have been developed in medical therapy, diagnosis, and research. By now, more than 3000 hospitals hold licenses from the Atomic Energy Commission to use radioisotopes. In addition, many thousands of doctors, dentists, and hospitals have X-ray machines that they use for some of the same broad purposes. One of the results of all this is that every month new uses of radioisotopes are developed.

Part 2

More persons are trained every year in methods of radioisotope use and more manufacturers are producing and packaging radioactive materials. This booklet tells some of the successes achieved with these materials for medical purposes.

What Is Radiation?

Radiation is the propagation of radiant energy in the form of waves or particles. It includes electromagnetic radiation ranging from radio waves, infrared heat waves, visible light, ultraviolet light, and X rays to gamma rays. It may also include beams of particles of which electrons, positrons, neutrons, protons, deuterons, and alpha particles are the best known.

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