For several reasons I think you'll be fine.

DMSA does not get into the brain to a significant extent. If you want to reduce the level of mercury in your brain you'll want to learn about Cutler Protocol. Andy Cutler explains the basics in this discussion with Dr Dan Pompa. Both had a typically long list of mercury symptoms, struggled to get a good diagnosis and got much improved. You'll have to right click the link at this site and download the mp3.
http://web.archive.org/web/20130413185932/http://www.healthcentersofthefuture.com/DrCutler/

I'm fairly sure Cutler's view was it is okay to chelate with titanium present.

I have a rod in my leg and I've done quite well during my years of Cutler detox--mostly DMSA + ALA plus a small number of rounds with DMPS. I mostly had a lead and cadmium problem.

I've not been seeing reports of nasty side effects when titanium was present.

Sorry to hear about the brain surgery. I hope all is going well with that.