How long does chronic PTT take to heal?

I developed PTT in April after continuing to train on a sprained ankle. I got new orthotics and I was supposed to cut my mileage, but I continued to train for ultramarathons. Now its on the verge of being chronic, and my podiatrist is talking about putting me in a cast, but I read on another thread that casts don't really work that well.

I cut my weekly running mileage from 80km/week to 30 km/week about 5 weeks ago, and it didn't really seem to help much. I stopped running completely 4 days ago. It actually hurts more when I haven't run for a few days.

I'm just wondering if there is anything that physiotherapy could do for somebody like me? If do I just need to rest/ice it? I am using an elliptical trainer (about 1 hour per day) as cross training while I am resting.

I am currently 205 pounds. Does weight loss help this condition?

Do you think a spring marathon is out of the question?