I empathize with your concerns. I can only imagine the worry that comes with having a child. My parents must have gone through hell when the doctors discovered a tumor behind my right eye. Fortunately it was benign (biopsy when I was 6) and they removed it when I was 7. It was attached to the optic nerve so I am thankful that I didn't lose vision in that eye.
Has he been exhibiting any new and/or unusual symptoms lately? What have doctors said about the swollen lymph nodes and his health in general?
I'm definitely with you over radiation concerns. Along with all the scans I had when I was 6-7, I had a CT brain scan, chest film, neck x-ray, and TMJ x-ray about 10 years ago (headache) and over the last 8 years x-rays and MRI's for numerous sports injuries/RSI.
Hoping good health and good fortune to you and your son in 2014 and beyond.