Unfortunately, no. The version of the Forum software we use does not have a way to "unfollow" a thread you've participated in. The 2.0 version does have a mod which allows this -- but SMF 2.0 breaks the theme.
At some point, proteus will have time to port the theme to SMF 2.0, and everyone will be much happier. For now, though, we're all out of luck.