Cindy,
a "boost" is typically given for advanced cancer patients. The typical amount of radiation is around 72 Gy, the ""boost" would bring it to 81 Gy. I missed a few treatments from being very ill. This did not please the radiation oncologist. I also missed a few treatments because of machine downtime. All of my missed treatments were made up and I received the entire amount.

My oncologist told me that persons not completing their course of treatment have significantly higher mortality rates. If pain is the issue, then they can adjust his pain management meds. If dehydration is the issue, they can rapidly rehydrate him in infusion -he will immediately feel better (being dehydrated makes you feel like crap).
Either my wife or a friend drove me to every treatment (it was a 60 mile round trip). Since radiation was my primary mode of treatment (with Cisplatin as an adjunct) missing radiation wasn't an option as I didn't want to die. You should be with him for these last 7 treatments (obviously not actually in the treatment room).

You need to express your feelings and your fears to him. You may want to have a private talk with his radiation oncologist as well.

I have had some bad "vamps" (blood takers) and I have had some some good ones. Ask for a pediatric needle -it's a lot less painful. Also bruising is a lot worse when dehydrated.