I had SBRT and the mask was uncomfortable, not painful. This was because I had to lay completely still to avoid paralyzing the spinal cord, since C2-C5 were affected. The mask didn't fit well around the jaw area, and I had to jut my jaw out to fit the mask during the procedure. The side effects were minimal. The pain had slowly decreased over the past 6 months as the tumor has stopped growing. I have been able to drive the past month since I need to take less pain meds. The pain has been the hardest thing to deal with, but it is slowly decreasing.