Any exposure to natural or man-made radiation, even at a very low level, carries a cancer risk. This is according to a National Academies of Science report. Yet experts also stress that most of the sources of radiation — from natural “background” exposures to medical X-rays and CT scans — probably increase the chance of developing cancer only slightly.

Even at the highest end of what experts consider low-dose lifetime exposure — 100 millisieverts — “about one person in 100 would develop cancer,” says Ethel Gilbert, a biostatistician at the National Cancer Institute. To put that number in context, she notes that 42 other lifetime cases of cancer can be expected in that same population of 100. Those cases would be due to smoking, environmental toxins or other factors.

CT scans are one source of concern, however. An abdominal CT scan has an exposure of about 10 millisieverts, which is quite a high dose. People should try to avoid being exposed to unnecessary radiation. Children are particularly vulnerable to unnecessary radiation because their organs are still developing. Alternative imaging techniques that don’t use radiation, such as MRIs or ultrasounds, may be available.

People may have a CT scan to check for disease when they don’t have any symptoms. These people may have to pay for the scan out of their own pocket because they are not covered for preventive screenings. Paramount requires prior authorization for imaging.

Natural, unavoidable background radiation includes exposure from naturally occurring radon, cosmic rays and earthborn radiation. It makes up 82 percent of the radiation the average American will be exposed to in a lifetime. Most of the remaining 18 percent of exposure comes from man-made sources such as medical X-rays, nuclear medicine and consumer products.

If you visit an emergency room (ER), the staff may perform tests that aren’t necessary because they don’t know your medical history and need to make a diagnosis. This is why it’s important to know when to go to the ER and when to go to your Primary Care Physician (PCP). Your PCP already knows your medical history. When in doubt, call your PCP’s office.

If you’re planning to have a CT scan or other imaging procedure and are concerned about radiation, talk with your PCP.