TECHNETIUM

Nuclear energy, including its tiny releases in radioactivity, has many more applications than producing electric power (at present only the heat to produce the power). One of these is nuclear medicine for both diagnostics and therapy, and here is an application of which I have only recently become aware.

When my bladder was removed five years ago, the prostate gland should have been removed with it, but the doctor (who has since died) left in a piece of it by oversight. It has now also turned cancerous and has to come out on the 21^st December. I plan to survive the operation because I have a lot more trouble to make.

But to come to the interesting point, untreated prostate cancer ultimately spreads to the bones, and until the advent of nuclear medicine, there was no easy way to fund out whether it had spread to the bones, for they will simply appear opaque to X-rays, regardless of whether they contain cancer cells. But a radioisotope (technetium) injected into the blood will collect in the bones, especially where they have cancer cells. This "tracer" emits gamma rays and the position of the sources can be monitored; a computer program then integrates the measurements into an image in which the radiation-emitting technetium shows up. Cancer cells are darker spots in the already dark bones. The skeleton (plus kidneys) shown in the picture is that of your editor (rear view), and no, the cancer has not spread to the bones. (It is quite fascinating to see your own skeleton gradually painted on the picture tube as the scanner moves over your body.)

Technetium has a half-life of 6 hours, long enough for the tracer to accumulate in the bones after the injection (2 hours) and to enable the scanner to monitor the body from front and back (45 minutes), yet short enough to lose most of its radioactivity during the day.

But if the halflife is so short, how do hospitals manage to keep it in stock all the time? By keeping a cow from which to milk it. The cow is a radioactive isotope of molybdenum with a halflife of 66 hours, which produces the technetium milk as it decays. There are now companies that supply hospitals with molybdenum isotopes, themselves produced by reactors and (neutron beam) irradiators that the antinukes want to outlaw.