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21 November 2009

Answer to Question #1990 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:

I recently went for some x rays of my left hip and was concerned when the technician couldn't get the view the doctor wanted. She took a total of eight x rays that day, and I'm concerned about the amount of radiation that I may have received on my left ovary, my cervix, and other organs in the x-ray area. Can you tell me how much radiation I might have absorbed? Is it as much as I would have gotten from a CT scan of the area? I chose not to have one because of the high radiation.

It's very hard to give accurate doses from secondhand information. Radiation dose depends on the exposure parameters employed by the institution (specific values of kVp and mAs) as well as the specific geometry of the exposures (angles, distances between subject and machine, how much of the organs were within the field of view). I took standard dose estimates from documents published by two well-accepted advisory bodies: the National Council on Radiation Protection and Measurements (NCRP) and the International Commission on Radiological Protection (ICRP). The doses are:

NCRP Publication 100, eight hip x rays:

Dose to ovaries: 16.8 mGy (1,680 mrad)
Dose to red marrow: 31.2 mGy (3,120 mrad)

ICRP Publication 62, one pelvic CT:

Dose to ovaries: 23 mGy (2,300 mrad)
Dose to red marrow: 5.6 mGy (560 mrad)

These numbers were actually provided by a public resource that uses published data from these sources. You can go to this source to see the data directly or make other comparisons. According to these standard values, the dose to the ovaries was somewhat lower than a pelvic CT, but the dose to marrow may have been a bit higher. If we compare a risk-weighted dose to the whole body, the values are 6.64 mGy (664 mrem) for the eight hip x rays and 7.1 mGy (710 mrem) for the CT, roughly comparable. Again, these values should be taken as approximate, as they may have employed different exposure parameters than were actually used in your study.

Michael G. Stabin, PhD, CHP

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