Radioactive Diagnosis

Among the fascinating new problems of medical research is how to use radioisotopes--forms of normally stable elements made radioactive in atom smashers. Radioisotopes have already become helpful in irradiating and arresting cancer. Lately, researchers have achieved even more significant results in cancer diagnosis. Because radioisotopes tend to concentrate in certain organs or diseased tissues, physicians have been able to detect tumors as much as six months before they appear on conventional X rays. Result: an important head start in the treatment of those that are malignant.

What makes radioisotopes so valuable is that they can be used selectively. Isotopes of iodine, for example, incorporate in the thyroid gland, where they can be used in both the detection and treatment of cancer, in some cases even eliminating the need for surgery. Fluorine, a related element, has a radioactive isotope (F18) that concentrates in bones, facilitating the detection of bone cancers.

Best for Brain. Dr. John Laughlin of Manhattan's Sloan-Kettering Institute reports nitrogen 13 and oxygen 15 highly effective in studying lung diseases. An entirely artificial element, technetium 99, produced by nuclear bombardment of molybdenum in a reactor, is rated by most medical centers as the best for detecting tumors of the brain. Both the gases and technetium have the advantage of short half-lives--that is, they lose half of their radioactivity in hours, or at most a few days. Thus, their radiation is so short-lived that it will not harm the patient exposed to it.

Radioisotopes have come a long way since the dawn of the atomic age. In the first years of nuclear medicine, they could be made only at atomic energy centers, and had to be shipped long distances to hospitals. To remain effective, they had to have longer half-lives, which meant that their radioactivity persisted in the bodies of patients. The newer, short-lived isotopes can be made in cyclotrons scattered across the country. They can be used within hours or even minutes of their production.

Bone to Blood. Current interest is focused on two isotopes of indium and gallium. At Ohio State University, Radiologists William W. Hunter Jr. and Xavier J. Riccobono worked with indium Ill, which was produced in the campus cyclotron. Using a special scanner, they found that the radioisotope concentrated heavily in bone in the first 24 hours after intravenous injection. As a result, X-ray photographs taken after the first day tended to reveal bone cancer. Even better, the radioactive molecules then joined proteins in the blood, concentrating in young, fast-growing tumors, thus revealing the sites of other cancers.

Such revelations have been surprisingly accurate. In one case, In-111 disclosed a lung tumor six months before it became visible on X rays. In another, the scanner showed a cancer six centimeters wide. From the operating room, the pathologist studying the growth phoned Hunter to say that the radiologist had been wrong--the cancer was only three centimeters wide. Later, he corrected himself; more careful examination revealed a spread of malignant cells through the six-centimeter zone.

100-to-1. The front runner among today's diagnostic radioisotopes is gallium 67. Like indium, it can be virtually hand-crafted any time in any cyclotron. It, too, has a half-life of approximately three days--just right for selective concentration in a series of body tissues.

At Oak Ridge Associated Universities, Biologist Raymond L. Hayes and Physician C. Lowell Edwards have given Ga-67 intravenously to 84 patients. At first it shows no selectivity between normal and tumor tissues. But after 48 hours the concentrations are enormously different in diseased and healthy areas: 10 to 1 for some blood cancers, and as high as 100 to 1 in muscle cancer. Ga-67's spectrum of cancer selectivity is probably the widest of any radioisotope.

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