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. View this table: Table 1095275. IVUS Analyses in Various Brachytherapy Trials IVUS should be performed with motorized transducer pullback, and volumetric as well as mean cross-sectional area (CSA) analysis should be reported. Because lesion lengths vary among trials, longer lesions may have larger stent, lumen, and neointimal volumes. Therefore, mean planar analysis (in which measured volumes are normalized for lesion length) may be a preferable way to compare different studies. Understanding lesion effects is more straightforward than understanding edge effects. (1) Edge analysis was not performed in all studies (Table 1). (2) Some studies combined proximal and distal edges and analyzed them together; others analyzed proximal and distal edges separately. (3) Edge analysis requires a larger sample size because of the wider range of possible responses. (4) It may be hard to determine the relationship between the source, the injured segment, and the IVUS images to assess geographical miss. Angiographic guidance may work in stented lesions; even in stented lesions (which are often radiolucent), however, meticulous comparison of IVUS and angiographic studies is necessary. (5) Some studies …