CT Scan Radiation Exposure FAQs

What is the radiation dose to a patient who has three chest CTs in a year? What is the risk?

The effective radiation dose for a chest CT will vary between patients, but the typical effective dose for a standard chest CT is 7 mSv. Therefore, this patient's dose from 3 standard chest CTs equals 21 mSv.

If the benefits of the three CT scans are justified, then the benefit completely outweighs the risk from the radiation dose.

What should I do to limit my risk of radiation exposure if I am having multiple CT scans?

If you are having frequent medical imaging procedures that are typically above 3 mSv each in any one year, or if you are changing your health care provider, then it is a good idea to keep your own record and track your radiation dose in mSv. This informs your doctor, helps to maximize the benefit, and minimizes the risk to you from multiple CT scans.

For patients who are scheduling a CT scan, what factors should be considered for reducing their radiation dose?

Patients and their referring physicians should discuss the radiation risks of a CT scan, as well as the risks of not having the CT scan (i.e. potentially compromising an accurate diagnosis). A radiologist should be consulted if there remains a question whether or not a CT scan should be performed.

Once you arrive for the CT, ask the CT technologist if appropriate measures for radiation dose reduction will be used. For example, the scanned area should be limited to the region of the body specified by your referring physician. The CT technique factors should be adjusted to the size of each patient's body. Newer scanners will adjust the radiation exposure automatically and reduce the exposure.

Repeated CT scans should be avoided, and certainly if the scans are being repeated only because the physician does not have access to the images from a recent CT scan. Usually the patient may request that their CT images be loaded onto a CD which they can take with them to their doctor's office. This service is usually available for nuclear medicine, PET, conventional radiology and mammography.

What is being done to reduce the amount of radiation dose from CT scans?

Manufacturers of CT scanners have made great strides in reducing dose. Newer CT scanners have built in dose saving features designed to provide the lowest dose while preserving the image quality.

Pediatric protocols are routinely available and used to significantly reduce the dose when compared to adult doses. When children need a CT scan, parents should ask about the right dose for their child's age and size.

For more information, visit The Alliance for Radiation Safety in Pediatric Imaging's "Image Gently" Campaign.

Is there anything I can take to counteract the effect of radiation exposure from CT scans?

No, unlike a flu shot or vaccination, there is nothing you can take to counteract the radiation effect from CT scans.
For the most part, background radiation exposure is unavoidable. To limit your radiation exposure from medical sources, it is important to talk to your doctor about your imaging choices. It is important to realize that in a properly performed individual exam, the potential health benefits almost always outweigh the potential risks of radiation exposure.

If a medical imaging procedure is indicated, then patients should not hesitate to schedule it.

How do radiation doses from a PET scan compare with CT scans?

A whole body PET scan (primarily used for tumor imaging) has an average radiation dose of 14.1 mSv compared to CT of the abdomen and chest which has an estimated radiation dose of 14 mSv [1].

Can screening for cancer with CT cause cancer?

Typically, CT is not used as a screening modality, but only as a diagnostic modality for patients displaying certain symptoms. Full body CT used to screen for cancer is not encouraged or recommended by any medical organizations currently [4].

In most cases, the benefit of having a diagnostic CT far outweighs the risk of not having the exam. This is because forgoing a CT exam may result in not obtaining appropriate clinical diagnosis or treatment. For single procedures resulting in doses below 50 mSv or for multiple procedures over short time periods resulting in a total dose of 100 mSv , "predictions of hypothetical cancer risk in patient populations exposed to such low doses are highly speculative and should be discouraged [2]."

To reduce unnecessary radiation exposure, inform your referring physician about previous CT examinations.