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Background-Restenosis within stents may be prevented by ionizing radiation from an intravascular source. Methods and Results-A liquid ␤ Ϫ radiation ( 188 Re) balloon was evaluated in a randomized and blinded porcine coronary model of stent restenosis. Group A pigs (nϭ17) received 0,16, 22, or 29 Gy at 0.5-mm depth, followed by stenting. Restenosis was quantified by angiography, ultrasound, and histomorphometry at 30 days. Group B (nϭ7) was stented first and then treated with 0 or 29 Gy with follow-up at 60 days. There was a measurable effect at 16 Gy, which improved with increasing doses. At 29 Gy, the histological stenotic area was reduced by 67% (22% versus 66% in controls, PϽ0.001). Radiation after stenting was equally effective; the stenotic area was reduced (21% versus 65%, PϽ0.001). At 16 Gy, the vessel just distal to the stent was significantly smaller than control vessels because of intimal thickening (Pϭ0.003). Radiated vessels had distinctive histology consisting of neointimal fibrin and reduced smooth muscle cells and matrix (PϽ0.0001). Conclusions-188 Re balloon brachytherapy in porcine coronary arteries results in dose-dependent and injury-independent inhibition of stent restenosis for up to 60 days. Restenosis at the borders of the irradiated zone is a potential limitation and may be related to underdosing. Brachytherapy with the 188 Re balloon appears to be safe and feasible for clinical studies. (Circulation. 2000;102:3117-3123.)

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