2 things i've experienced:
1. general, daily variances in swelling, puffiness, soreness, & skin color. My husband says my neck/face looks slightly different every day. The docs have said that is to be expected due to the changes of surgery & radiation (I had both)
2. infection. I've had several rounds of infection. Now I wait a few days and see if the symptoms get worse before I call the docs. With infection the stiffness, warmth of skin, redness gets noticeably worse. Last April I waited until my next regularly scheduled dr visit before I said anything, but meanwhile a puffy spot popped open leaking pus, then I had an open pathway between the inside of my mouth and my chin (sorry to be so gross). That was waiting too long. Now I recognize the symptoms and call sooner for antibiotics - which work.

From your message I am a little confused about the IMRT - did he have it a year ago or doing it now?

If you can try telephoning your cancer docs & describing the symptoms first it might help on some of that confusion about which doc to go to. Let the doctors know if he has a fever, increased fatigue, and when it started.
Good luck,
michelle