hi there.. I just wanted to add something. Not to freak you out but so you are aware.
Having a CT scan is equivalent to anywhere from 50-1000 xrays (depending on where you are getting it done).. It is a significant form of radiation. They are not prohibited because they are useful diagnostic tests and when death is the other option (for ruling out strokes, for example) then yes, of course, they will give you your 10th head CT in the face of something deadly. They will not prohibit that.
Also, CT's are more likely to be done more frequently in the elderly since the effects of CT's are sometimes not seen for 20+ years.
A responsible doctor should be discussing these risks with you if you have had 1 CT in the past year. It is not an unfounded fear and is documented in medial literature. They have some sort of radiation "dosing" guide to help them make clinical decisions if a CT is required or not. For example, I went to emerg in Mar 2011 with what appeared to be a partial seizure and the doc would NOT let me have another head CT since I'd just had one in Sept 2010. He booked an MRI instead.
So my point is, there are real risks. Do some research if it'll make you feel better. But in the end, what's been done can't be undone and for the vast majority of people it is fine. Especially if they were medically necessary. But please try to be honest with docs and let them know who much radiation you've had (xrays, ct's etc) so they can be smart about their choices. And, the effects of this stuff, like I said, don't always become apparent for many many years.
In the meantime, have your doctor monitor your blood (CBC) and watch out for swollen nodes, esp. in the areas you've had scanned.
I, too, have had lots of radiation exposure this year. I also worry. You are SO not alone.