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CLINICAL STUDY

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

Manuscript received March 5, 2002; revised manuscript received April 24, 2002, accepted May 31, 2002.

^* Reprint requests and correspondence: Dr. Bonni Syeda, Department of Internal Medicine II, Division of Cardiology, University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria.
bonni.syeda{at}akh-wien.ac.at

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.

Abbreviations and Acronyms   %DS   percent diameter stenosis   GM   geographical miss   ISR   in-stent restenosis   MLD   minimal lumen diameter   RIL   reference isodose length   ROC   receiver operating curve   START   Stents and Radiation Therapy registry

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