The dose distribution around the edges of an improved32P source for endovascular brachytherapy: a Monte Carlostudy

摘要

Endovascular brachytherapy has proven to be an effective tool inthe reduction of restenosis following balloon angioplasty for coronaryheart disease, while the range of optimal doses and precise targettissue are still unknown. However, over-dosing has been associated withincreased thrombogenicity and permanent damage to vessel walls.Under-dosing has been found to stimulate neointima formation, causingrestenosis. It has been suggested that restenosis near the edges (edgeeffect) of the intervention may be caused by the dose falloff towardsnear the source ends. Monte Carlo code EGS4 was used to calculate thedose distribution around the ends of a Guidant 32P source. Atthe ends of the source the 100% isodose curve was found to bend backtoward the source starting at about 3 mm from the end of the activesource (prescription to 2 mm radius). The 80% isodose line crossed theprescription line 1 mm from the source ends. Further calculationspredicted improvement can be achieved by changing the specific activitywithin 1 mm of the ends of the source. A four-fold increase in specificactivity in 0.5 mm segments at the ends of the source, followed by a 0.5mm gap between the ends and the middle part of the source, kept the 100%isodose line at the prescription distance to within 0.5 mm of the activelength of the source without any over-dosing. With five times theactivity in the terminal segments, a “full length source” isachieved, involving a small over-dosing