Effect of intracoronary γ-radiation therapy on in-stent restenosis: An intravascular ultrasound analysis from the gamma-1 study

Background - The aim of this study was to use serial volumetric intravascular ultrasound to evaluate the effect of γ-radiation on recurrent in-stent restenosis. Methods and Results - After successful reintervention, patients were randomized to receive either ¹⁹²Ir or placebo. Intravascular ultrasound studies with motorized pullback (0.5 mm/s) were performed immediately after irradiation and at 8-month follow-up in 70 patients. Paired volumetric analysis of the stented segment and of 5-mm proximal and distal reference segments was performed; this included measurements of the external elastic membrane, lumen, plaque and media (external elastic membrane minus lumen), stent, and intimal hyperplasia (stent minus lumen). Baseline proximal reference, stent, and distal reference measurements were similar in both groups. The changes in proximal and distal reference measurements of the external elastic membrane, plaque and media, and lumen areas were similar in both groups. However, the decrease in stented segment lumen volume was less in the ¹⁹²Ir patients than the placebo patients (-25±34 mm³ versus -48±42 mm³; P=0.0225), and the increase in the volume of intimal hyperplasia in the stented segment was less in the ¹⁹²Ir patients than in the placebo patients (28±37 mm³ versus 50±40 mm³; P=0.0352). When averaged over the length of the stented segment (32±13 mm versus 33±14 mm; P=0.9), the increase in mean area of intimal hyperplasia was 0.8±1.0 mm² in the ¹⁹²Ir group and 1.6±1.2 mm² in the control group (P=0.0065). Late stent-vessel wall malapposition was noted in one placebo patient and no ¹⁹²Ir patients. Conclusions - γ-Radiation therapy can effectively prevent recurrent in-stent restenosis by inhibiting neointimal formation within the stent. At the stent edge, there were no significant differences between ¹⁹²Ir and placebo patients.