I am worried about cancer due to radiation because i have had 4 brain ct scans in a year.plus a heart ct before brain surgery.plus 3 contrast dyes.

Past: Your radiation exposure already happened and very unlikely cause any abnormality. Time to move on. You can not change the past and risk is very low.

Your cancer risk is : Though there is some data that exposure to ct radiation may cause cancer in some individuals. The exposure has to be substantialy prolonged to allow the cumulative dosage to have cancerogenec effect.

I call this syndrome: 'worrying about termites in the outhouse when you have a fire on the porch.' imaging increases population risk, but individual risk is only slightly altered. Why you had brain surgery and the need for a 'heart ct' before the surgery are porch smoke if not fires, forget the outhouse worry.