Answer to Question #12962 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

During a recent upper gastrointestinal (GI) series, I was subject to a beam-on time of 5.6 minutes, and a radiation dose of 302 milliGray (mGy). Both numbers seem excessively large to me, given that an effective dose for a "typical" upper GI appears to be three to six milliSieverts (mSv). Can you please help me translate the given radiation dose into an effective dose?

A

Often the terms used in radiation protection physics can be confusing. The dose a patient receives from fluoroscopy depends on many things: the equipment used, the size of the patient, and the imaging features employed. All of these are automatically set by the machine. 

You indicate that your total dose was 302 mGy, and the length of the exam was 5.6 minutes. This indicates that the dose rate was 54 mGy/minute. According to literature, dose rates less than 72 mGy/minute should be achievable. So, it appears that this dose rate was not excessive. 

Fluoroscopic scan times also vary due to complexity of the case and the methods used by the physician. The literature reports that times may range from less than 2 to more than 10 minutes. So again, it does not appear that your time of 5.6 minutes is excessive.

Physicists use the term effective dose in units of mSv to compare doses from different modalities or procedures. This term is meant to convey a relative risk to a population, not the specific dose to an individual. This is because it encompasses different shapes, sizes, genders, and ages of people. 

Typical effective dose values for an upper GI scan range from 3–9 mSv. The calculation takes into effect the size of the area irradiated, so an effective dose cannot be calculated for your case without knowing this area. 

The statement below is from the American Association of Physicists in Medicine Position Statement on Radiation Risks from Medical Imaging Procedures:

"At the present time, epidemiological evidence supporting increased cancer incidence or mortality from radiation doses below 100 mSv is inconclusive. As diagnostic imaging doses are typically much lower than 100 mSv, when such exposures are medically appropriate, the anticipated benefits to the patient are highly likely to outweigh any small potential risks."

You should feel free to bring your concerns to your primary care physician or the facility that performed the scan who may have additional information regarding your particular scan. 

Joseph Och, MS, DABMP

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.
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