What is brachytherapy and how is it done?
When treating coronary artery disease with angioplasty or stents, an ongoing problem has been the high incidence of restenosis – a recurrence of coronary artery blockage at the site of treatment. One option for patients who have developed restenosis in previously implanted stents is coronary artery radiation, or brachytherapy.Most restenosis is caused by thrombosis, or blood clotting, at the site of treatment. This type of restenosis can be partially prevented by using anti-clotting drugs.
But some restenosis is due to actual tissue growth at the site of treatment. It is likely that much of the restenosis that proves to be untreatable by repeat angioplasty may be due to this “tissue growth restenosis.” Such tissue growth – a proliferation of the “endothelial” cells that normally line blood vessels – cannot be prevented effectively with anticoagulants. (Note: this is the kind of restenosis that is greatly reduced with drug-coated stents.)
How does radiation therapy affect restenosis?
It has been known for decades that radiation can kill cells and prevent tissue growth. This, after all, is the mechanism by which radiation therapy can be effective in treating cancer.So it makes perfect sense that radiation – if it can be targeted accurately, and with appropriate doses – might be able to treat the restenosis often seen after stent placement. Radiation therapy aimed at restenosis has two purposes: to treat the restenosis itself (by killing the cells that have re-occluded the stent), and to prevent further restenosis (by inhibiting tissue growth).
How is intra-coronary radiation given?
Intra-coronary radiation is administered during a special heart catheterization procedure. The radiation itself is delivered by a new type of catheter designed to apply radiation to a localized area. The catheter is passed into the coronary arteries, and across the target area. (The “target area” is the area of restenosis that is to be treated.) Once the targeted area of stenosis is “bracketed” by the catheter, the radiation is applied.Two varieties of radiation have been used so far – gamma radiation and beta radiation. Both kinds of radiation are cumbersome to use, and require the presence of special equipment in the lab, the adoption of special precautionary procedures, and the presence of specially trained individuals, including a radiation oncologist. Investigators who have used intra-coronary radiation systems agree that a key to avoiding problems is the experience of the operator. These are complex procedures that require more than the standard expertise of the interventional cardiologist.
