I had the same thing and was put on prednizone for three months.. It made me feel better right away but I blew up..It cleared everything up but the discomfort in my chest took several months to subside and I still have some of it now and I am about 9 months out since my last radiation.
Speak with a Pulmonologist and get evaluated along with your Onc and Radilogist. If you have Radiation pneumanitisis you want to ge tthat treated so you don't develope scar tissue. Or as little as possible.