Medical radiation probably sparks off about 200 cancers a year in the UK.
If "background" radiation for Jo Average is 1 day, a Chest X-Ray is about 3 days.
Back X-Rays are about 5 months.
CT of the belly is about 4-5 years.
This is one of the reasons GP's don't rush to fill in the x-ray form, (not 'cos they don't love you or they're protecting a budget.)
Have a look at Making the Best Use of a Department of Clinical Radiology by The Royal College of Radiologists.