title: Safety of beta radiation exposure to the non-target segment: an intravascular ultrasound dosimetric analysis.
abstract: BACKGROUND
  The use of longer radioactive seed trains to avoid geographic miss may lead to greater radiation exposure to distal vasculature due to the natural tapering of coronary arteries. The aim of this study was to use IVUS-based dosimetric analysis to evaluate the effect of beta-radiation on angiographically normal, noninjured distal segments.
  
  
  METHODS
  We analyzed 17 in-stent restenosis cases (stent length: 20 +/- 8 mm) treated with a 40 mm 90Sr/Y source train. The prescribed dose was 18.4 Gy (reference less than or equal to 3.3 mm) or 23 Gy (reference > 3.3 mm) at 2 mm from the source. Noninjured, but fully radiated, distal reference sites were determined by angiography. Based upon the three-dimensional vessel contours obtained at baseline, the minimum dose delivered to 90% of plaque volume (Dv90) was determined. Vessel, plaque and lumen volumes and Dv90 were computed in every 2 mm subsegment (n = 52).
  
  
  RESULTS
  On average, no significant serial change was observed in plaque area (5.0 +/- 2.5 mm3/mm post-treatment to 5.6 +/- 3.1 mm3/mm at 8-month follow up; p = 0.09), vessel area (10.2 +/- 3.7 to 10.3 +/- 4.0 mm3/mm; p = 0.84), or lumen area (5.2 +/- 2.0 to 4.7 +/- 1.8 mm3/mm; p = 0.19). Subsegment analysis, however, revealed a wide range of dose distribution, with a significant positive correlation between Dv90 and plaque increase (p = 0.008), as well as vessel change (p < 0.001), representing dose-dependent positive vessel remodeling following beta radiation. Consequently, no significant relationship was observed between Dv90 and lumen change.
  
  
  CONCLUSIONS
  Detailed IVUS-based dosimetric analysis demonstrated that beta radiation promoted positive remodeling, preventing lumen loss despite a mild increase in plaque mass on angiographically normal, noninjured distal segments.
authors.affiliation: Stanford University, Stanford, California, USA.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Kaneda
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Honda
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Morino
authors.forename: Tim
authors.initials: T
authors.lastname: Fox
authors.forename: Ian
authors.initials: I
authors.lastname: Crocker
authors.forename: Alexandra J
authors.initials: AJ
authors.lastname: Lansky
authors.forename: Paul G
authors.initials: PG
authors.lastname: Yock
authors.forename: Raoul
authors.initials: R
authors.lastname: Bonan
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Fitzgerald
mesh_terms: D000368:Aged; D001610:Beta Particles / Q000009:adverse effects* / Q000627:therapeutic use*; D017023:Coronary Angiography; D023903:Coronary Restenosis / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D003331:Coronary Vessels / Q000000981:diagnostic imaging / Q000473:pathology / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011874:Radiometry; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional / Q000379:methods*