Hi, Margie
do you happen to have dental work that could be causing scatter onto your lips? Probably not but a question couldn't hurt.

You wrote - "One thing I intend to ask on Thursday is why the radiation is targeting the opposite side of my mouth, when all the initial analyses, including CT/PET scans did not show any metastasizing to any other area at all."

The target volume delivered to the tumor and other areas that would be likely candidates for it spreading will be as per guidelines (such as the NCCN ones on the site) and your doctors' judgement. In addition, there is going to be scatter to areas where they don't want the radiation to go, but can't just tell it to go in 2.5 inches, then stop. Your RO should be able to show you how the radiation is being painted on the tumor; if he hasn't discussed this with you in detail, don't be afraid to ask.