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Geographical miss during intracoronary irradiation: impact on restenosis and determination of required safety margin length

Bonni Syeda, MD, MSc^*,*, Peter Siostrzonek, MD^*, Rainer Schmid, MD, Paul Wexberg, MD, BM^*, Christian Kirisits, MSc, DSc, Stefan Denk, MD^*, Gilbert Beran, MD^*, Ali Khorsand, MSc, DSc^*, Irene Lang, MD^*, Boris Pokrajac, MD, Richard Potter, MD and Dietmar Glogar, MD, FESC^*

^* Department of Internal Medicine II, Division of Cardiology, University of Vienna, Vienna, Austria
Department of Radiotherapy and Radiobiology, University of Vienna, Vienna, Austria

View larger version (16K): [in a new window]   Figure 1 Segmental distribution of radiation dose. (a) Segment of full-dose irradiation with >90% of reference dose at 1-mm vessel depth (= reference isodose length [RIL]). (b) Segment between end of injury and end of RIL receiving full-dose radiation with >90% of reference dose at 1-mm vessel depth (= safety margin). (c) Segment of dose fall-off with 10% to 90% of reference dose at 1-mm vessel depth (= edge of irradiation). This segment was assumed 4.5, 2.0, and 2.5 mm proximal and distal to the end of the active source for 192Ir, 32P, and 90Sr/Y application, respectively (11). (d) Segment of negligible irradiation with <10% of reference dose at 1 mm vessel depth.

View larger version (27K): [in a new window]   Figure 2 Analyzed segments in patients with no geographical miss (GM) (A) and GM (B). (a) Injured segment with full-dose radiation. For comparison with the median length of injured segments without full-dose irradiation in patients with GM (segment e in Fig. 2B), this segment was equally set to 4 mm. (b) Distance between end of injury and end of reference isodose length (full dose irradiation zone). (c) Edge of irradiation (dose fall-off zone). (d) Distance between end of dose fall-off zone and outermost injury (negligible irradiation zone). (e) Length of GM.

View larger version (19K): [in a new window]   Figure 3 Sensitivity and specificity curves for prediction of geographical miss in relation to various safety margins per vessel. Determination of the cut-off point with equal sensitivity and specificity (7.8 mm; 83.7% sensitivity/specificity). In order to achieve 95% specificity, a safety margin of 9.9 mm is required per vessel.

View larger version (15K): [in a new window]   Figure 4 Receiver operating characteristic curve demonstrating the performance of different safety margins for prediction of geographical miss. Area under the curve: 0.92.