Comparison of brachytherapy strategies based on dose-volume histograms derived from quantitative intravascular ultrasound

Purpose. We present in this paper the comparison, by simulation, of different treatment strategies based either on β- or γ-sources, both with and without a centering device. Ionizing radiation to prevent restenosis is an emerging modality in interventional cardiology. Numerous clinical studies are presently being performed or planned, but there is variability in dose prescription, and both γ- and β-emitters are used, leading to a wide range of possible dose distributions over the arterial vessel wall. This paper discusses the potential merits of dose-volume histograms (DVH) based on three-dimensional (3-D) reconstruction of electrocardiogram (ECG)-gated intravascular ultrasound (IVUS) to compare brachytherapy treatment strategies. Materials and Methods. DVH describe the cumulative distribution of dose over three specific volumes: (1) at the level of the luminal surface, a volume was defined with a thickness of 0.1 mm from the automatically detected contour of the highly echogenic blood-vessel interface; (2) at the level of the IVUS echogenic media-adventitia interface (external elastic lamina [EEL]), an adventitial volume was computed considering a 0.5-mm thickness from EEL; and (3) the volume encompassed between the luminal surface and the EEL (plaque + media). The IVUS data used were recorded in 23 of 31 patients during the Beta Energy Restenosis Trial (BERT) conducted in our institution. Results. On average, the minimal dose in 90% of the adventitial volume was 37 ± 16% of the prescribed dose; the minimal dose in 90% of the plaque + media volume was 58 ± 24% and of the luminal surface volume was 67 ± 31%. The minimal dose in the 10% most exposed luminal surface volume was 296 ± 42%. Simulations of the use of a γ-emitter and/or a radioactive source train centered in the lumen are reported, with a comparison of the homogeneity of the dose distribution. Conclusions. It is possible to derive DVH from IVUS, to evaluate the dose delivered to different parts of the coronary wall. This process should improve our understanding of the mechanisms of action of brachytherapy.