Dose-volume histograms based on serial intravascular ultrasound: a calculation model for radioactive stents

Background and purpose: Radioactive stent are under investigation for reduc tion of coronary restenosis, However, the actual dose delivered to specific parts of the coronary artery wall based on the individual vessel anatomy h as not been determined so far. Dose-volume histograms (DVHs) permit an esti mation of the actual dose absorbed by the target volume. We present a metho d to calculate DVHs based on intravascular ultrasound (IVUS) measurements t o determine the dose distribution within the vessel wall. Materials and methods: Ten patients were studied by intravascular ultrasoun d after radioactive stenting (BX Stent, P-32, 15-mm length) to obtain tomog raphic cross-sections of the treated segments. We developed a computer algo rithm using the actual dose distribution of the stent to calculate differen tial and cumulative DVHs. The minimal target dose. the mean target dose, th e minimal doses delivered to 10 and 90% of the adventitia (DV10, DV90), and the percentage of volume receiving a reference dose at 0.5 mm from the ste nt surface cumulated over 28 days were derived from the DVH pints. Results were expressed as mean +/- SD. Results: The mean activity of the stents was 438 +/- 140 kBq at implantatio n. The mean reference dose was 111 +/- 35 Gy, whereas the calculated mean t arget dose within the adventitia along the stent was 68 +/- 20 Gy. On avera ge, DV90 and DV10 were 33 +/- 9 Gy and 117 +/- 41 Gy, respectively. Expandi ng the target volume to include 2.5-mm-long segments at the proximal and di stal ends of the stent. the calculated mean target dose decreased to 55 +/- 17 Gy, and DV90 and DV10 were 6.4 +/- 2.4 Gy and 107 +/- 36 Gy, respective ly. Conclusions: The assessment of DVHs stems in principle to be a valuable too l for both prospective and retrospective analysis of dose-distribution of r adioactive stents. It may proc ide the basis to adapt treatment planning in coronary brachytherapy to the common standards of radiotherapy. (C) 2001 E lsevier Science Ireland Ltd. All rights reserved.