HI there... I was very similar to you in my diagnosis... it sounds to me like it was not Base of tongue but oral tongue cancer you have. My node was a bit smaller than your's but other than that it sounds very similar.

You will get through it as your life depends on it.

Bring in some music maybe. Close your eyes and take your meds. It will not hurt - it is painless. Radiation is cumulative you will feel it likely starting at week three with the worst of it being the two weeks following your treatment. It will just be generalized pain, redness, blistering, tiredness.

Get a good cream for your neck and face area where the rads will be aimed. Eat as much as you can now, stock up on boost, ensure for later when swallowing becomes a problem etc... try to get high protein, and high calorie ones as nutrition is very important to healing.
If they give you a peg remember to swallow regardless, even if it's a little luke warm water. Preserving this reflex is imperative.

remember to make a baking soda rinse and use it frequently as it promotes healing.

I was shocked at being locked into the table too. Eventually, it isn't an issue.

try not to be afraid. you'll be okay.

hugs and sorry you have to be here.