Pierre Jannin’s group in Rennes developed a nice system for DBS planning and guidance based on Slicer and PyDBS. You can download an overview paper from here. Maybe @mholden8 can give you more details or can help you get in contact with them.
If you only need DBS lead segmentation, then I think Segment Editor’s Grow from seeds effect could work very well. You may need to crop and resample the volume using Crop volume module (to have high, anisotropic resolution so that region growing can follow the leads more robustly). You should be able to segment multiple leads at once, specifying one small seed segment for each, and a larger seed for “other”.
I would be happy to help with this, too, but of course I need much more accurate description of what you did, what you expected to happen, and what happened instead.