Low-Dose Radiation Used to Prevent Restenosis in Leg Arteries

Originally Published MDDI January 2002

R&D DIGEST

Low-Dose Radiation Used to Prevent Restenosis in Leg Arteries

Peripheral arterial disease (PAD) occurs when blood vessels or arteries in the legs become blocked. A study being conducted at Rush-Presbyterian-St. Luke's Medical Center (Chicago) is exploring a novel treatment for PAD, which affects approximately 40% of people over age 70 to some degree. Symptoms of PAD can include numbness in the feet, pain, cramping or burning sensations in the legs, and decreased mobility.

Conventional treatment of patients with PAD include angioplasty and placement of a stent; however restenosis occurs in 50–80% of patients treated in this manner. Interventional cardiologists at Rush are assessing the use of a catheterization technique accompanied by low-dose radiation to prevent restenosis. They speculate that the radiation will work in much the same way it does when used to prevent restenosis from occurring in arteries in the heart.

Patients enrolled in the study will be treated with a device called the RDX Peripheral Radiation Delivery System, which is being developed by Radiance Medical Systems (Irvine, CA). The system is considered unique because the radiation source is integrated into the membrane of the balloon catheter. The researchers indicate that results of previous studies have shown that using radiation inside the catheter is effective, but incorporating the radiation into the balloon compresses the blockage onto the sides of the artery, which seems to be more effective at lowering restenosis rates.

According to Jeffrey Snell, MD, codirector of the Cardiac Catheterization Laboratories and principle investigator of the study, the trial is called "radiation after PTA is done," or RAPID. Snell says the inflated balloon is brought into complete contact with the leg vessel wall to provide uniform and complete coverage and distribution of the radiation. The researchers believe that the device is well suited for treating large arteries in the leg because penetration depths of the beta isotopes are limited to 4 or 5 mm in tissue or fluid.

According to Snell, "After surgery, renarrowing of the peripheral arteries happens because cells in the artery wall divide and proliferate as a healing response to the injury caused by the angioplasty balloon or stent placement. Low-dose local radiation therapy actually inhibits the cells' ability to respond in this way, thereby substantially reducing the renarrowing response." He adds that "this is significant because the arteries in the leg are larger than the chest so the radiation needs to penetrate completely to have any effect."

The catheter used in the RAPID trial is administered through the femoral artery using angioplasty techniques similar to those used for treatment of heart disease. To treat PAD patients, the cardiologist directs the catheter down the leg to the blocked area where the balloon at the tip is expanded to open up the blockage. Patients return for checkups at 30 days, 6 months, and 12 months.

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