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Radiation Improves Angioplasty

While the widespread use of tiny flexible tubes called stents has greatly improved the outcomes for heart patients receiving angioplasty, cardiologists still find that the arteries of almost one-quarter of these patients will become clogged again in a process known as restenosis.

Recent clinical trials - some conducted at Duke University Medical Center - have demonstrated that small measured doses of radiation delivered immediately after an angioplasty procedure reopens a clogged stent and can keep the arteries from re-clogging. This approach has significantly reduced the number of times patients must have repeat procedures to keep their arteries open, the researchers say.

It is estimated that more than 100,000 patients in the United States need treatment for restenosis annually.

Currently, Duke is one of the few institutions to offer two new and different approaches to radiation treatment - one is based on beta radiation, the other based on gamma radiation. Both systems were approved for use in November by the Food and Drug Administration (FDA). Duke performed its first procedures since approval this month.

"More than 75 percent of the approximately 1 million Americans who receive angioplasty procedures each year also receive a stent, and of those patients, about 25 percent will experience restenosis," said Duke cardiologist Dr. Michael Sketch Jr. "Before the advent of radiation treatments, there was nothing out there proven effective for restenosis."Radiation has the same potential for making a huge impact on the treatment of restenosis as stents have made on the treatment of new blockages," said Sketch, who serves as director of the cardiac catheterization laboratories at Duke.

In an angioplasty procedure, a tiny balloon is threaded through an artery to the site of blockage, where it is inflated, pushing the atherosclerotic plaque to the side. In more and more cases, cardiologists will then deploy a stent, a tiny wire mesh tube designed to keep an newly cleared artery open.

However, while this process opens a larger channel for blood to flow through, it also stimulates the abnormal growth of the cells lining the artery, which can then re-block the treated artery. Past clinical trials have shown that when delivered at the same time the artery is re-opened, the radiation interferes with the endothelial cells proliferative response.

"When the balloon is inflated, it causes damage to the lining of the artery," explained Dr. Tim Shafman, a radiation oncologist who works with Duke cardiologists. "The body responds by growing new endothelial cells at the site. While the exact reasons why radiation works is unclear, we do know that it seems to inhibit the growth of these cells."

The researchers add that radiation also is used in other medical conditions to control the abnormal growth of tissue.

Beta radiation has been used for decades to treat keloids, large growths of scar tissue on the skin caused by proliferation of normal tissue in response to an injury. When treated with a small amount of radiation after removal, the keloids seldom returns. Radiation also is being used at Duke to prevent the abnormal proliferation of bone cells after total hip replacement.

The recently completed START (STents And Radiation Therapy) trial of the Beta-Cath system demonstrated that the incidence of restenosis was 36 percent to 66 percent lower in patients treated with the system when compared to placebo. The START trial was conducted at 50 sites, including Duke, under the direction of Brigham and Women's Hospital in Boston. The Beta-Cath system was developed by Novoste Corp., Norcross, Ga.

The Beta-Cath system uses strontium-90 as its source of beta radiation, while the Checkmate system uses iridium-192 as its source of gamma radiation. The Checkmate system, developed by Cordis Corp., of Miami, was shown in the recently completed Gamma I trial to have 41 percent fewer instances of restenosis when compared to placebo. The Gamma I trial was conducted at 12 hospitals, including Duke, under the direction of Washington Hospital Center in Washington. To date, the two types of systems have not been compared to each other in a clinical trial.

"In both systems, the radiation is caused by the slow disintegration of the source elements, and from the patients' perspective, it doesn't really matter which source is used," Shafman said.

The radiation is applied after the balloon angioplasty device is withdrawn from the patient. A slender hollow tube is inserted through the artery to the site of treatment. Once at the site, small seeds of radiation are sent through the tube to the area to be treated. At no time does the solution leave the device and come into contact with tissue, Sketch said, and the radiation only travels a short distance from its source.

For a beta procedure, the radiation remains in the patient for about three to five minutes, while the gamma approach requires about 20 minutes. When gamma radiation is used, physicians and technicians must remain behind a lead shield during treatment.

There are many factors that cardiologists use when determining which approach to use, one of the most important being the size of the lesion, or area of treatment. The Beta-Cath system is approved for lesions up to 20 millimeters long, while Checkmate is approval for lesions up to 45 millimeters.

"The important thing for heart patients at Duke is that we have at our disposal the latest techniques and technologies for treating heart disease," Sketch said. "We should be able to make a great impact in the outcome of our patients. With both systems here at Duke, we can evaluate which one is the best for each individual patient."