Optimization of dose distributions for bifurcated coronary vessels treated with catheter-based photon and beta...

The dose distributions in the bifurcated vessels treated with a catheter-based delivery system are complicated by the geometry of bifurcation consisting of a main and a branch vessel at different angles, and it is difficult to generate satisfactory dose distributions. We hypothesize that increasing the number of dwell positions can result in better dose distributions. An optimization method based on the simulated annealing was developed to demonstrate the validity of this idea. In this method, the source in the branch treatment was allowed to take up to five dwell positions. A cost function was constructed to deliver the prescription dose to the planning targets with penalties for both overdosing and underdosing. By using the optimization algorithm, it was found that for 90 degrees to 60 degrees bifurcated vessels an optimized single dwell position treatment scheme can be as effective as the schemes that include up to five dwell positions. As the bifurcation angle becomes smaller than 60 degrees, the dose distributions generated with the single dwell position scheme become less satisfactory than the more complicated treatment schemes with multiple dwell positions. By using a three-dwell-position treatment scheme for the 192Ir source, the overdosing can be kept under 166% even at a bifurcation angle of 20 degrees.