I went away a week after rads last year. I was fine, but my skin was fine throughout rads. By the end of my 20 sessions it was just a bit pink. I didn't particularly keep it covered up either (I know, bad person), just used the usual sun cream that I ususally use.
So I think it will depend on how your skin is. My skin generally is quite tought, I don't burn easily. I have since has 2 more holidays in the sun, one in Greece and one in California and both times, not a problem.
12 months on you would never know that I had had anything like rads on my skin.
Also, whilst I was having rads last year it was good weather here and I used to sit quite happily in the garden sunbathing and never had a problem.
Sounds like your specialist nurse either doesn't like the sun or jealous that you are going away.