Automatic determination of needle and source positions for brachytherapy of the prostate using 125Iodine Rapid Strand.

Abstract

Brachytherapy using 125I Rapid Strand as a permanent implant is now widely used for the treatment of prostate cancer. Manual treatment planning can be time-consuming and has provided the incentive to develop a computer planning algorithm for automatically determining the needle positions and source loading required to produce a clinically acceptable dose distribution. The algorithm uses a method analogous to that used in simulated annealing. A needle with associated source positions is selected randomly from those possible. A number of source positional and dose volume histogram constraints for the prostate, rectum and urethra have to be satisfied before an objective function is evaluated that provides a measure of the dose distribution to the prostate. The objective function is gradually improved using an iterative process until a final solution is reached. The algorithm is used to plan six patients which have previously been manually planned and which are selected to represent the range of prostate volumes encountered in practice. A clinically acceptable dose distribution is obtained that is shown to be as good as manual planning in all cases.