Nuclear Medicine: Enabling Advanced Diagnostics and Therapies

Nuclear medicine involves the use of radioactive materials for either diagnosis or treatment. Until the 1950s, the technology was confined to diagnostic X-rays and radiation treatments for cancer and a few other diseases. Today, it is used in the most sophisticated diagnostic studies and surgical procedures, and includes such subspecialties as nuclear cardiology.

For diagnostic X-rays, relatively low doses of ionizing radiation are beamed through soft tissue onto photographic film, where they make denser tissue, such as bone, stand out.

For therapy, radiation is given in larger doses that kill body tissues by destroying the ability of cells to grow and divide normally. It is especially lethal to tissue that grows fast, with a rapid rate of renewal. This is why it is effective in shrinking and eventually eliminating cancerous tumors. Today, half of all cancer patients receive some form of radiation therapy.

Because radiation cannot distinguish between cancerous and normal tissue, it also damages healthy cells, particularly in the skin, the linings of many internal organs, and the bone marrow, where blood cells are made. If the radiation dosage is not too high, most normal tissue will eventually repair itself. Thus, the challenge is to find a dosage that will kill a cancer without rendering permanent damage to the healthy surrounding tissue. Complicating matters is the fact that radiation damage is cumulative. Even low-level environmental, or background, radiation contributes to the buildup.

The Newer Technologies

As medical researchers learn more about the harmful effects of radiation, they are developing ever safer ways to use it. New technology allows doctors to implant tiny radioactive seeds in some types of tumors to shrink or destroy them while sparing healthy tissue. This approach is now being used for prostate cancer and certain inoperable tumors.

In treating other cancerous growths, computers enable therapists to calculate the precise dosage required and new machines beam radiation directly to the tumor. In still other instances, chemicals carry radiation to an organ without exposing other parts of the body. For example, the use of radioactive iodine often removes the need for surgery in the treatment of an overactive thyroid gland; the thyroid absorbs the iodine, and the radiation destroys part or all of the gland's hormone-making tissue.

New X-ray equipment also delivers less radiation than in the past. The newest mammography machines, for example, require less than one-third of the amount of radiation needed only 20 years ago. In addition, the injection of minute amounts of radioactive particles that can be followed by special gamma cameras allows doctors to study internal organs with less radiation and more accuracy than is possible with X-ray machines alone. For instance, a radioactive material called thallium is used in making heart scans that pinpoint areas where the cardiac muscle is not getting enough blood.

Despite the tremendous advances in nuclear medicine, it is important to realize that there is still a risk involved in exposure to any radiation. Avoid routine diagnostic X-rays unless their benefit clearly outweighs the risk. Hence, the potential risk of an annual chest X-ray is greater than the possible benefits for a healthy person. In contrast, mammography every one or two years for women over the age of 50 is currently recommended because the risk of breast cancer is much higher than any known hazards of this X-ray examination.

Radiation and Birth Defects

X-rays and other forms of ionizing radiation are especially harmful to a developing fetus; they can cause severe birth defects or even fetal death. Any woman who is pregnant, or who may be pregnant without knowing it. should not be X-rayed. If an X-ray is absolutely necessary, a protective lead shield should be used to cover the fetus.

Even before conception, radiation can cause birth defects by damaging the father's sperm or the mother's eggs. With time, a man's ability to produce healthy sperm usually returns. But a woman does not make new eggs: she is born with her lifetime supply. Fortunately, surgical techniques now allow the ovaries to be moved out of the field of exposure during radiation therapy, and later returned to their normal position.

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