CT scan for brain concerns

I'm getting a CT scan for my brain soon due to some progressive symptoms that could be from a tumour. My concern is that I saw that the chances of getting cancer from a CT scan is 1 in 2,000 from a single scan... So if I don't have cancer, I'm now going to have a high risk of it ? I don't understand why an MRI wouldn't have been better?

I'm not one to worry about health stuff usually but this actually worries me.