: Radioisotopes in Medicine by Phelan Earl W - Nuclear medicine

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

Radioisotopes in Medicine

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.

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 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 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 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 , 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 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.

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