James Richard Fromm
Radioactive isotopes produced in nuclear reactors have a wide variety of uses, from the illumination of clock dials and the operation of smoke detectors to space borne power sources, but we consider here only their uses in medicine. These uses fall into two categories: the use of isotopes as the diagnostic tools called radiotracers and the use of the destructive effects of nuclear radiation, called radiation therapy, which finds its major use in the treatment of cancer.
The use of radiotracers depends upon the fact that the chemical behavior of the different isotopes of the same element is essentially the same. For the isotopes of hydrogen the mass difference is relatively large and significant differences in their chemical behavior can be observed, but for heavier elements no difference is detectable. As a consequence the path taken by a radioactive isotope of an element, inserted into a living body in place of the normal stable isotopes of that element, will be the same as the path taken by the usual form of the element. The path can be followed by monitoring the radioactive decay of the isotope, which is called a tracer. Isotopes used as tracers are chosen to have short half-lives and radiation which is minimally damaging.
The employment of radiation therapy involves the use of isotopes, or less often even accelerators, external to the body to produce intense and destructive local irradiation. It is also possible to use radioisotopes which are implanted in the body and later removed, or less often the radiation of an isotope used in the manner of a radiotracer.