Answer to Question #1877 Submitted to "Ask the Experts"

Let's take these in a different order. A "radioisotope" (actually the more correct general term is "radionuclide" but the former is commonly heard) is simply a radioactive element. All of nature is made up, as I'm sure you know, of atoms. Some of these atoms are, to our perception, "stable," meaning they don't change form. Others have an excess of one or another type of particle in their nucleus, and so rearrange themselves to achieve stability. In doing so, they give off particles or rays of energy (this is "radiation"—the atoms themselves are "radioactive," they give off "radiation" while seeking stability).

Radiation has many beneficial uses, such as in medicine, biological tracers, production of electric power, and so on, but it can also damage living organisms if they are exposed to too much. So the key is to monitor and control the beneficial uses of radiation so that the benefits are obtained without harm to people or the environment (this is one definition of the science of "health physics"). In medicine, there are a number of radionuclides, generally labeled to different molecules, that are used in diagnosing and treating disease.

To my knowledge, ³²P is used mostly in treating certain diseases of the bone and marrow. ³²P is given in one or two forms (pure phosphate or chromic phosphate), generally between 185-370 MBq (5-10 mCi). ¹³¹I is used to diagnose as well as to treat diseases of the thyroid (as the thyroid has a natural affinity for iodide) and is labeled as well to some anticancer drugs (such as monoclonal antibodies) in attempts to treat cancers. Small amounts of activity, less than I cited for ³²P, are used in diagnosis and greater amounts will naturally be used for therapy. In all of these cases, radiation dose calculations are performed by competent health physicists to assure that the medical information or treatment can be obtained without exposing the patient to too much radiation.

Your question about "what risks are posed" from all uses of radionuclides is a bit too broad to be considered here—there is much printed literature and information on the Internet about this. This is a somewhat controversial topic; you will hear many points of view if you study this topic in any depth. Our Web site has more on this if you search under "risks."

Lastly, an "autoradiograph" is an image made on normal photographic film from exposure to radiation. Radiation darkens film (this is one of the ways it was first discovered), and some experiments use film exposure to "take a picture" of where radioactive material may have been in some biological or physical system, usually for research purposes.

Michael G. Stabin, PhD, CHP
Assistant Professor of Radiology and Radiological Sciences