Bill...My heart truly goes out to you as a fellow phobia person...closterphobia and severe anxiety disorder...As others are saying the mind is a powerful powerful tool either it is you friend or your foe...the trick is to make it your friend..I understand from the depths your fears arise...I am the same way thats why the suggestion of focusing on your breathing and I added humming to myself although not sure if you can do that during radiation treatments....I had some tests done where they did scopes I was relaxed during the first part but the moment they tried to go down my throat I paniced and they had literally force me and hold me down...I had nightmares for months after of drowning...having the feeding tube gave me the same sence of being choked...although I knew logically that it wasn't hurting me I could not let it go... It is a matter of trusting who is working with you...I made a connection with my nurse practicioner and well when I was having trouble with my feeding tube after surgery I asked for her...when I saw her and her determined eyes working on my tube and not letting anyone else do what they wanted to do (take it out and put it back in with the aid of an xray machine) I relaxed and drifted off...I know this is going to be the hardest feat to do in your life but believe me you CAN do it! I have not thank god have to have radiation and a mask and if faced with the same issue I know I would be in a spot...Try to learn to trust relax.. what ever it takes for you....Please don't give up...When all is said and done you will have so much more to be proud of also conquer fears wow...like I said for me it is a matter of detatching from myself or concentrating on something focusing on something other than what is scaring me... and trusting you will be ok and you will!!

Persistance pays off...hypnosis, accupuncture, meditation anything that may work but keep trying!!!