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

Objectives The goal of this study was to evaluate the incidence and effects of underdosage of injured segments during intracoronary irradiation and to define the minimal length of safety margin required to avoid mismatched source placement. Background Underdosage of injured segments due to misplacement of active source has been suggested as the underlying mechanism for the occurrence of edge restenosis. Methods Baseline angiograms of 112 vessels in 109 patients with in-stent restenosis undergoing coronary reintervention followed by intracoronary irradiation (192Ir: Checkmate, Cordis, Miami, Florida; 32P: Gallileo, Guidant, Houston, Texas; 90Sr/Y: Beta-Cath, Novoste, Norcross, Georgia) were analyzed. The distances between the outermost injury and outermost end of “reference isodose length” (RIL), defined as a segment with ≥90% of reference dose at 1 mm vessel wall depth, were measured. “Safety margin” was defined as the distance between the outermost injury and outermost end of the RIL, “geographical miss” (GM) as a complete injured segment not being covered by the RIL, and “restenosis” as the percent diameter stenosis >50%. Results Baseline angiographic analysis was performed for 224 edges in 112 vessels. Geographical miss was found in 46 (20.6%) edges. The incidence of target lesion restenosis within the 78 vessels with available follow-up was 43.3% for patients with GM versus 14.9% for patients with no GM (p = 0.005). Analysis of various injured segments exposed highest restenosis rates in injured segments with negligible irradiation (27.8%) in comparison with injured segments with dose fall-off (16.7%) or injured segments with full-dose irradiation (7.7%) (p = 0.006). Receiver operating curve analysis revealed a safety margin of 10 mm required per vessel (i.e., 5-mm safety margin/edge) to achieve 95% specificity of GM. Conclusions Geographical miss is associated with a higher incidence of restenosis at the corresponding edges. Restenosis was more pronounced in injured segments with negligible irradiation than in injured segments at the dose fall-off zones. We recommend a safety margin of 10 mm per vessel to minimize GM.