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Radiation therapy keeps arteries clear

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3:46pm, January 29, 2001
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Each year, about 500,000 people in the United States have their clogged heart arteries cleared by angioplasty. In the costly, sometimes risky procedure, a surgeon reopens the artery by inserting, inflating, and then removing a tiny balloon. But for about half the patients, the treated artery reclogs within 6 months.

Two new studies add to a growing body of evidence that radiation applied within an artery might reduce that recurrence rate.

Recently, surgeons have been inserting stents, or metal mesh cylinders, into arteries after angioplasty to hold them open longer. However, the stents don't always avoid the problem of repeat clogging, or restenosis, caused by the buildup of scar tissue from injury during angioplasty.

Earlier studies suggested that among patients with stents, those exposed briefly to a localized dose of radiation are significantly less likely to have the stent become clogged than are patients who received no radiation (SN: 6/14/97, p. 364).

In one of the new studies, the largest of its kind, researchers treated 252 patients who had clogged stents. All had chest pain and impaired blood flow to their heart—two conditions resulting from blocked arteries.

Clinicians replaced the stents or cleared the stent area by angioplasty or with a tissue-removing tool. They then placed a string of iridium-192 pellets inside the treated arteries of roughly half the patients for up to 20 minutes. Iridium-192 emits gamma rays, which thwart the scarring process. The rest of the patients, the study's control group, received a similar but nonradioactive string.

As expected, arteries closed back up within 6 months in 51 percent of the control group. But only 22 percent of patients who received radiation experienced a relapse, says study coauthor Paul S. Teirstein, a cardiologist at the Scripps Clinic and Research Foundation in La Jolla, Calif. He and his colleagues report the findings in the Jan. 25 New England Journal of Medicine (NEJM).

There's a catch. One of the side effects of the radiation, the investigators found, was an increase in blood clots, which can cause heart attacks. Replacing a stent also may lead to blood clots.

But "we think we've solved that problem," says study leader Martin B. Leon, a cardiologist at Lenox Hill Hospital in New York. He says that doing fewer stent replacements and treating patients with anticlotting drugs for 8 weeks after radiation can bring the risk of clot formation down to that of the control group.

In a related study also published in the Jan. 25 NEJM, surgeons in Europe performed first-time angioplasty on 181 patients. Immediately after the procedure, researchers randomly assigned patients to receive one of four different doses of radioactive yttrium-90�which emits beta rays�within their arteries. Surgeons delivered the radiation from a small wire inside a catheter. They removed the apparatus after 2 to 3 minutes.

After 6 months, the relapse rates in the groups ranged from 4 to 28 percent according to radiation dose—the more the radiation, the fewer patients relapsed.

"The study shows that it is possible, with the use of [beta radiation], to . . . mimic the natural defense mechanisms against atherosclerosis," or the process of arterial clogging, says study coauthor William Wijns, a cardiologist at the Cardiovascular Center, OLV Hospital in Aalst, Belgium.

Although the results of the two new studies seem promising, says Mark J. Eisenberg, a cardiologist at the Jewish General Hospital in Montreal, the use of radiation against restenosis is "really in its infancy." He notes that data from these and previous studies have been limited to a year or less of follow-up.

"There's a danger in widespread dissemination of a technology before its long-term effects are known," he cautions. "For a potentially dangerous technology, we would like to have at least 5 years of follow-up."

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