Answer to Question #11591 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

What are the effects of radiation exposures received from bone density measurements, with special emphasis on gonadal dose?

A

Most bone density measurements today use a technique known as dual-energy x-ray absorptiometry (DEXA), commonly referred to as a DEXA scan. The standard DEXA scan usually uses a very narrowly collimated fan x-ray beam to scan the lower lumbar spine encompassing the vertebral bodies L1–L4. DEXA scans are considered to be a low-dose exam.

For a standard posterior/anterior (PA) spine DEXA scan, the gonadal dose can range from 0 to 16 micrograys (µGy). Other common techniques are the forearm/wrist, proximal femur (where the femur connects to the hip), or whole-body technique. Gonadal doses from the forearm/wrist technique are essentially zero. The gonadal doses from the proximal femur technique range from 1 to 255 µGy per scan, and from the whole-body technique, they range from 4 to 77 µGy per scan, depending on the DEXA scanner used for the exam.

The typical effective dose from a DEXA scan ranges from 0.2 to 60 microsieverts (µSv) for the PA spine technique, less than 1 µSv for the forearm/wrist technique, 0.2 to 50 µSv for the proximal femur technique, and 4 to 77 µSv for the whole-body technique, depending on the DEXA equipment used. These are very low doses.

To compare the doses from a DEXA scan, we can consider the doses we receive naturally every day from background sources of radiation such as cosmic rays; terrestrial uranium, thorium, and other radionuclides in the soil; and naturally occurring radionuclides in our bodies. The average dose received annually in the United States from these sources is approximately 3,000 µSv per year or about 8.2 µSv per day.

Consequently, since the gonadal and effective doses from a DEXA bone density scan are so close to the natural levels of background radiation and well within the observed background variations around the average, we would expect to observe no gonadal or other radiation-related effects at all.

Michael J. Bohan, RSO

Reference
Conference of Radiation Control Program Directors. Technical white paper: Bone densitometry. CRCPD Publication E-06-5; October 2006. Available at http://crcpd.org/Pubs/BoneDensitometryWhitePaper.pdf; accessed 15 June 2016.

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