I just wanted to add that the types of tests your doc orders has a lot to do with your insurance. A couple of years ago, I went to see my doc cuz I kept getting dizzy. I was afraid I might have a brain tumor. But she refused to do any testing and assured me that I did not have a brain tumor. I pushed for an MRI and finally got one. It was negative for any brain tumors. Recently I noticed that when I go see the doc, she would order tests more easily. I realize now that back then I had HMO, now I have better insurance, my docs don't need permission from the insurance co. to order tests or send me to a specialist. When doctors can order tests or send you to a specialist without hassle, they'll do it also for fear of malpractice whether or not they think there is anything wrong with you. If they dismiss a symptom you have and you end up with stage-4 cancer the next month, they are in trouble.
It's a complicated issue. But maybe one solution is to ask for alternative tests that does not involve radiation. Last Oct when I experienced difficulty swallowing, my doc wanted to do a swallow study but I asked for an upper-endoscopy instead. It's more involved and more expensive but I'm glad I got it done and avoided the radiation. Unfortunately, sometimes there are no alternative tests.