In prostate cancer patients receiving EBRT, when, if ever, do you use MRI to change your seminal vesicle coverage?

Yes! I routinely get MRI as part of planning. This obviously helps with delineation of median lobe and prostate apex, but can also show involvement of the SV.

I do not reduce elective coverage based on MRI images, because the decision to treat SV is related to risk of microscopic involvement. Howev...