title: Evaluation of three rhenium-188 candidates for intravascular radiation therapy with liquid-filled balloons to prevent restenosis.
abstract: BACKGROUND
  Intravascular brachytherapy is an effective method for inhibiting coronary restenosis after percutaneous transluminal coronary angioplasty. A new concept for preventing restenosis is the use of a liquid-filled balloon containing a beta-ray-emitting radioisotope. Generator-produced rhenium-188 (Re-188) is a good candidate for intravascular brachytherapy. However, in the unlikely event of balloon rupture, release of Re-188 perrhenate may cause a high radiation dose to the thyroid and stomach. In this study, we compared the biodistributions of three Re-188 preparations (Re-188 perrhenate, Re-188 pentetic acid [DTPA], and Re-188 MAG3) to assess the radiation dose to organs in a rat model that mimicked balloon rupture.
  
  
  RESULTS
  After injection of Re-188 preparations intravenously, rats were killed at 10 minutes, 30 minutes, 60 minutes, 2 hours, and 6 hours (n = 5/group). Tissue concentrations were calculated and expressed as percent injected dose per gram or per milliliter. In addition, urine excretion and thyroid gland uptake were evaluated in rats (n = 5/group) with a gamma camera after administration of 37 MBq (1 mCi) of each agent. Our data showed all 3 agents were excreted primarily via urine. In the Re-188 MAG3 group, 82% was excreted within 1 hour, but in the Re-188 perrhenate group, only 28% was excreted. The biodistribution data for these agents revealed that radioactivity levels in the stomach and the thyroid gland were high in the perrhenate group but low in the Re-188 DTPA and Re-188 MAG3 groups. The concentration levels in other tissues including lung, liver, testis, muscle, and blood were low throughout this study for all 3 agents. The thyroid radiation values were 0.163, 0.0167, and 0.00728 mGy/MBq for Re-188 perrhenate, Re-188 DTPA, and Re-188 MAG3, respectively. The stomach radiation values were 0.127 mGy/MBq for Re-188 perrhenate, 0.013 mGy/MBq for Re-188 DTPA, and 0.0104 mGy/MBq for Re-188 MAG3.
  
  
  CONCLUSIONS
  In the event of balloon rupture, the release of Re-188 MAG3 or Re-188 DTPA results in lower radiation doses than release of Re-188 perrhenate, especially to the thyroid gland and the stomach.
authors.affiliation: Department of Nuclear Medicine, Taichung Veterans General Hospital, Taiwan. wylin@vghtc.vghtc.gov.tw
authors.forename: W Y
authors.initials: WY
authors.lastname: Lin
authors.forename: S C
authors.initials: SC
authors.lastname: Tsai
authors.forename: B T
authors.initials: BT
authors.lastname: Hsieh
authors.forename: T W
authors.initials: TW
authors.lastname: Lee
authors.forename: G
authors.initials: G
authors.lastname: Ting
authors.forename: S J
authors.initials: SJ
authors.lastname: Wang
mesh_terms: D015906:Angioplasty, Balloon, Coronary; D000818:Animals; D001918:Brachytherapy; D003327:Coronary Disease / Q000532:radiotherapy*; D005069:Evaluation Studies as Topic; D005998:Glycine / Q000031:analogs & derivatives; D008297:Male; D004369:Pentetic Acid; D011829:Radiation Dosage; D011868:Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics / Q000627:therapeutic use*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012008:Recurrence; D012211:Rhenium / Q000493:pharmacokinetics / Q000627:therapeutic use*; D014018:Tissue Distribution
chemical_list: D011868:Radioisotopes; D019275:Radiopharmaceuticals; C015428:perrhenate; C096273:N-(mercaptoacetyl)glycine; D012211:Rhenium; D004369:Pentetic Acid; D005998:Glycine