Intravascular ultrasound assessment of the mechanisms and results of brachytherapy.

Serial intravascular ultrasound (IVUS) studies have shown that restenosis in nonstented lesions and late lumen loss in reference segments contiguous with both stented and nonstented lesions is a balance between arterial remodeling and neointimal hyperplasia. Conversely, in-stent restenosis (ISR) is neointimal hyperplasia.1,2 The present review focuses on lessons learned from IVUS about mechanisms of brachytherapy in preventing or treating restenosis. Most brachytherapy studies have included IVUS analyses, but to various degrees and with various methodologies. In some studies—eg, the Washington Radiation for In-stent Restenosis (WRIST) trials—serial (postirradiation and follow-up) IVUS was performed in the majority of patients. In other trials, IVUS was usually a site-specific substudy in small numbers of patients (Table 1). These studies assessed only the short-term (typically 6 to 9 months) effects of brachytherapy.