Answer to Question #11369 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT

The following question was answered by an expert in the appropriate field:

Q

My daughter had a computed tomography (CT) scan of her sinuses when she was 11. Now she is 13 and she needs x rays taken for a leg problem. I am very worried about the cumulative effect of radiation, and I have sleepless nights. I would like to know more about how much radiation she was exposed to during the CT scan. When I asked the medical professionals, they said she had received a dose length product (DLP) of 40.6 milligray per centimeter (mGy cm-1). That would be equivalent to 0.88 millisievert (mSv). I don't really understand how high this is compared to a chest x ray. The actual readings on the CT scan were 100 kilovolts (kV) and 50 milliamps (mA). Please help me. I am delaying the leg x rays for fear of too much exposure.

A

Thank you for using the Health Physics Society's Ask the Experts feature. I will provide information below that should help you sleep better and will allow you to consider going ahead with the x rays of your daughter's leg so she can benefit from the best available health care.

The Health Physics Society's position statement on radiation risk states:

"In accordance with current knowledge of radiation health risks, the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 50 millisievert (mSv) in one year or a lifetime dose of 100 mSv above that received from natural sources. . . . There is substantial and convincing scientific evidence for health risks following high-dose exposures. However, below 50–100 mSv . . . risks of health effects are either too small to be observed or are nonexistent."

This is similar to the American Association of Physicists in Medicine's (AAPM) position on radiation risks from medical imaging procedures:

"Risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent. Predictions of hypothetical cancer incidence and deaths in patient populations exposed to such low doses are highly speculative and should be discouraged."

The AAPM goes on to say, "These predictions are harmful because they lead to sensationalistic articles in the public media that cause some patients and parents to refuse medical imaging procedures, placing them at substantial risk by not receiving the clinical benefits of the prescribed procedures."

An effective dose of 0.88 mSv is well below the dose at which an increase in risk can be seen. The effective doses from extremity exposures are very low, much less than the CT scan. What this means is that any increase in your daughter’s cancer risk from the CT scan and leg x rays is minimal (if it exists at all) and is more than offset by the very real medical benefit gained by allowing your daughter's physicians to use diagnostic imaging to "see" what is going on.

These procedures provide a medical benefit to your daughter. The risk from diagnostic imaging procedures, when properly performed and clinically indicated, is very small compared to the diagnostic benefit they provide. I would personally not delay having leg x rays because of concerns about radiation exposure.

Kent Lambert, CHP

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 26 December 2015. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.