Dosimetry study of Re-188 liquid balloon for intravascular brachytherapy using polymer gel dosimeters and laser-beam optical CT scanner.

Angioplasty balloons inflated with a solution of the beta-emitter Re-188 have been used for intravascular brachytherapy to prevent restenosis. Coronary stents are in extensive clinical use for the treatment of de novo atherosclerotic stenoses. In this study, the effect of an interposed stent on the dose distribution has been measured for Re-188 balloon sources using the proprietary BANG polymer gel dosimeters and He-Ne laser-beam optical CT scanner. In polymer gels, after ionizing radiation is absorbed, free-radical chain-polymerization of soluble acrylic monomers occurs to form an insoluble polymer. The BANG polymer gel dosimeters used in these measurements allow high resolution, precise, and accurate three-dimensional determination of dosimetry from a given source. Re-188 liquid balloons, with or without an interposed metallic stent, were positioned inside thin walled tubes placed in such a polymer dosimeter to deliver a prescribed dose (e.g., 15 Gy at 0.5 mm). After removing the balloon source, each irradiated sample was mounted in the optical scanner for scanning, utilizing a single compressed He-Ne laser beam and a single photodiode. In the absence of a stent, doses at points along the balloon axis, at radial distance 0.5 mm from the balloon surface and at least 2.5 mm from the balloon ends, are within 90% of the maximum dose. This uniformity of axial dose is independent of the balloon diameter and length. Dose rate and dose uniformity for intravascular brachytherapy with Re-188 balloon are altered by the presence of stent. The dose reduction by the stent is rather constant (13%-15%) at different radial distances. However, dose inhomogeneity caused by the stent decreases rapidly with radial distance.