[Intracoronary radiotherapy (brachytherapy) for treatment of restenosis]

RESTENOSIS AFTER CORONARY ANGIOPLASTY: Restenosis after coronary angioplasty remains a common clinical problem. Even after the advent of stenting, the rate of restenosis is still to the order of 20% or even higher in certain patient subgroups. Treatment is difficult, particularly in case of diffuse restenosis within stent lumens. POTENTIAL CONTRIBUTION OF BRACHYTHERAPY: After stent implantation, restenosis is generally due to excessive intimal proliferation producing a "benign tumor" formation that progressively obstructs the arterial lumen. Endocoronary curietherapy has been proposed for its "antiproliferative" effect. SYSTEMS USED: Two radiation sources are used: gamma emitters with powerful tissue penetration properties, and beta emitters which exhibit less tissue penetration. Radioprotection is a greater problem with gamma emitters but dosimetry is more difficult to control with beta emitters. In clinical practice, the sources are placed close to the target site via conventional percutaneous catheterization and are employed as a complement to standard angioplasty used to destroy the stenosis. Endocoronary brachytherapy requires close collaboration between the interventional cardiologist and the radiotherapist.

After the preliminary feasibility studies, several randomized trials have assessed the contribution of brachytherapy in the prevention of restenosis. Using gamma emitters (192Ir), the SCRIPPS, WRIST and GAMMA-1 studies demonstrated good immediate safety and a real effect on restenosis with 50% reduction. Inversely, groups of treated patients have a higher rate of severe complications (death and infarction) related to late acute coronary thrombosis after interruption of antiplatelet therapy combining ticlopidin and aspirin. These complications result from the frequent introduction of stents during angioplasty procedures and by delayed endothelialization of the stents leaving a starting point for thrombosis formation longer than usual. The same type of complications have been observed with beta brachytherapy in the PREVENT trial, while in the START trial that used the 90Sr/y source in 476 patients, severe events were not more frequent in the irradiated group. In the latest trial, the frequency of new stent implantations was lower (21%) and antiplatelet treatment was maintained longer. Finally, the rate of restenosis was significantly lower (29% versus 45%).

Current data confirm the efficacy of endocoronary brachytherapy to limit intimal proliferation after angioplasty and reduce the rate of restenosis. The question of safety remains open, with the potential risk of late coronary thrombosis; no long-term data (more than 5 years) are available. It is undoubtedly too early to propose routine use of brachytherapy, excepting perhaps cases where interventional cardiology raises particularly difficult problems, for example in case of diffuse restenosis within an endoprosthesis.