Geographical miss during intracoronary irradiation: impact on restenosis and determination of required safety margin length.
OBJECTIVE
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 ((192)Ir: Checkmate, Cordis, Miami, Florida; (32)P: Gallileo, Guidant, Houston, Texas; (90)Sr/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.
Syeda
Bonni
B
Department of Internal Medicine II, Division of Cardiology, University of Vienna, Vienna, Austria. bonnie.syeda@akh-wein.ac.at
Siostrzonek
Peter
P
Schmid
Rainer
R
Wexberg
Paul
P
Kirisits
Christian
C
Denk
Stefan
S
Beran
Gilbert
G
Khorsand
Ali
A
Lang
Irene
I
Pokrajac
Boris
B
Potter
Richard
R
Glogar
Dietmar
D
D001610:Beta Particles / Q000009:adverse effects / Q000627:therapeutic use*; D017023:Coronary Angiography; D023921:Coronary Stenosis / Q000532:radiotherapy*; D005720:Gamma Rays / Q000009:adverse effects / Q000627:therapeutic use*; D006801:Humans; D015994:Incidence; D007496:Iridium Radioisotopes / Q000009:adverse effects / Q000627:therapeutic use; D009204:Myocardial Revascularization / Q000009:adverse effects* / Q000379:methods*; D010761:Phosphorus Radioisotopes / Q000009:adverse effects / Q000627:therapeutic use; D011446:Prospective Studies; D011835:Radiation Protection / Q000379:methods; D011879:Radiotherapy Dosage; D012008:Recurrence; D012449:Safety; D012680:Sensitivity and Specificity; D015607:Stents; D013326:Strontium Radioisotopes / Q000009:adverse effects / Q000627:therapeutic use; D016896:Treatment Outcome
D007496:Iridium Radioisotopes; D010761:Phosphorus Radioisotopes; D013326:Strontium Radioisotopes