That itchiness is healing, you know how when you get a burn and it starts to heal. I used OTC cortisone with aloe Vera when I had to be dressed and working. When I was home for the day I just kept the aloe going. I remember at the time, every day felt like an eternity. Now that much time has passed, it feels like it was a blip in time, I only remembered it when I read your post.
If you are concerned about using cortisone, I bet you could call the radiation center and ask if it would be safe since you are 7 weeks out.
Are you using any other skin moisturizers? Does it help?