The Clinical Value of Radioactive Isotopes

I AM very much honoured by your invitation that I should deliver an oration in this valuable and distinguished series that has been established in memory and honour of the life of Robert Campbell, and I wish to speak of the clinical value of radioactive isotopes. In the year in which the Robert Campbell memorial orations were founded, Rutherford had already detected faint scintillations on the screen of a chamber in which nitrogen atoms were being bombarded with helium nuclei (Rutherford and others, 1930). These scintillations were due to the formation of oxygen atoms from nitrogen, and the first isotope had been artificially produced. The ensuing thirty years have seen this subject develop in a way, and with a speed, that would have satisfied Campbell's instinct for the application of new knowledge and techniques; with the first radioactive isotope being prepared in measurable quantities in 1934 (Fermi and others, 1934), used in animals and in man soon after, and by 1942 in the treatment of human disease (Hamilton and Lawrence, 1942; Hertz and Roberts, 1942). Since then the clinical uses of these materials have increased rapidly. My title, however, is not the clinical uses, but the clinical value, of radioactive isotopes, for it has become obvious in the last few years that certain isotopes had more than a purely experimental interest and, to-day, their clinical use is essential, in the sense that certain of our patients will be improperly treated or inadequately investigated, without their help. And so I shall speak mainly about the methods that are of direct clinical importance. Even so, I shall need to illustrate rather than to enumerate all the present applications of radioisotopes in clinical medicine. I will be dealing in particular with radioactive iodine, which was one of the first to be produced, and to be used in therapy, and which is one in which my own department has been interested. It is perhaps a fitting example, also, since it has important applications to the investigation and surgery of the thyroid gland, which Robert Campbell so much advanced by his surgical skill and published work. I would like to start by explaining the meaning of some of the rather unfamiliar terms that are used in this subject, and those of you who are accustomed to work with isotopes and their radiations will, I hope, excuse this. So, firstly, what exactly is an isotope? You will remember, perhaps, that different atoms differ, not only in the weight of their nuclei, but also in the size of the electrical charges on them.