title: Centered versus noncentered source for intracoronary artery radiation therapy: a model based on the Scripps Trial.
abstract: BACKGROUND
  The Scripps Trial was a randomized study of intracoronary artery radiation therapy with iridium 192 used to treat restenotic vessels. We used the intravascular ultrasound data from the Scripps Trial to investigate whether a lumen-centered gamma or beta radiation source would reduce radiation dose heterogeneity compared with the noncentered source position used.
  
  
  METHODS
  Analysis included 28 patients with stent placement in 20 native vessels and 8 saphenous vein grafts enrolled in this trial. Radiation dosimetry for gamma radiation was calculated to deliver 800 cGy to the far field target, provided the maximum dose to the near field target did not exceed 3000 cGy. Prescribed dosimetry for beta radiation by use of yttrium 90 was 1600 cGy at 2 mm distance from the source.
  
  
  RESULTS
  The calculated average minimum source to target distance by use of a lumen-centered source increased by 0.18 mm from 1.70 +/- 0.25 to 1.88 +/- 0.36 mm, whereas the maximum distance decreased by 0.17 mm from 3.64 +/- 0.60 to 3.47 +/- 0.43 mm (P <.05). On the basis of these distances, the maximum radiation dose, as well as radiation dose heterogeneity (ratio of maximum to minimum), would have been reduced in 22 of 28 patients by use of a lumen-centered gamma or beta source (P <.005). The reduction in dose heterogeneity was substantially greater with a beta source compared with a gamma source (48% vs 16% reduction).
  
  
  CONCLUSIONS
  Centering of the intracoronary artery radiation therapy delivery catheter within the vessel lumen can significantly reduce radiation dose heterogeneity when compared with a noncentered source position. This dose reduction is substantially greater for a beta compared with a gamma source.
authors.affiliation: University of California at San Diego, La Jolla, Calif, USA.
authors.forename: Armin
authors.initials: A
authors.lastname: Arbab-Zadeh
authors.forename: Valmik
authors.initials: V
authors.lastname: Bhargava
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Russo
authors.forename: Craig S
authors.initials: CS
authors.lastname: Levin
authors.forename: Shirish K
authors.initials: SK
authors.lastname: Jani
authors.forename: Jennifer
authors.initials: J
authors.lastname: Lucisano
authors.forename: Paul S
authors.initials: PS
authors.lastname: Teirstein
mesh_terms: D001610:Beta Particles / Q000627:therapeutic use*; D023903:Coronary Restenosis / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005720:Gamma Rays / Q000627:therapeutic use*; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D015588:Observer Variation; D011879:Radiotherapy Dosage; D016032:Randomized Controlled Trials as Topic; D012044:Regression Analysis; D015607:Stents; D014463:Ultrasonography; D015021:Yttrium Radioisotopes / Q000627:therapeutic use
chemical_list: D007496:Iridium Radioisotopes; D015021:Yttrium Radioisotopes