Answer to Question #10188 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

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


We are using the C-arm in fluoroscopy procedures to perform modified barium swallow studies. One of our students "read somewhere" that C-arms give off a "lot of radiation." I have provided them with thyroid shields, leaded eyewear, and aprons. I ask them (during the exam) to step away when the unit is on.

Are there any articles that explain/educate nonradiation staff that their fear is unwarranted. One student thinks she might become pregnant so refuses to do fluoroscopy. A doctor puts on a lead apron and stands behind the leaded walls.

Could you provide me with some basic information for them?


Radiation exposure to staff involved in fluoroscopy procedures arises from two main sources—"scattered" radiation from the patient and "leakage" radiation from the x-ray tube. Regulations are in place that limit the amount of leakage radiation an x-ray tube can emit and all x-ray tubes must meet that limit when they are manufactured. Of the two sources of exposure, it is the scattered radiation that varies considerably and is the higher contribution of exposure to the fluoroscopy staff. By knowing what causes the variations in scatter, one can use that knowledge to minimize exposure.

The scattered radiation at a specific location is affected by a number of factors including the patient (and machine parameters), the field size, and the scattering angle. Larger patients and thicker body parts require more radiation to produce an acceptable image for the physician. It follows that if more radiation impinges on the patient, the amount of scattered radiation increases as well. Field size refers to the size of the radiation field where it enters the patient. Not surprisingly, as the field size increases, so does the scatter. Finally, the scattering angle is also important, mainly because people sometimes incorrectly assume that they should avoid standing on the opposite side of where the beam enters the patient because the x-ray beam would be "pointing" at them. In fact, the area of highest scatter is on the same side where the x-ray beam enters the patient. This is called "backscattered" radiation—think of it as the radiation "bouncing" off the patient in a backward direction. That is where the scattered radiation is the highest. While the patient size and thickness is somewhat beyond the control of the machine operator, utilizing as small a field size as possible (referred to as "coning down") not only decreases the scattered radiation to the staff, but also reduces the area of the patient's skin exposed to x rays—a double benefit. Understanding the "backscatter" concept allows staff to position themselves in a location where the scattered radiation is lower.

Leaded aprons, thyroid collars, and lead eyewear are very effective in reducing the scattered and leakage radiation to very low levels. In terms of pregnant or potentially pregnant staff participating in fluoroscopy procedures, a "wrap-around" (i.e., covers all sides of the user) lead apron generally provides plenty of protection, especially when it is used in conjunction with other protection methods that you have suggested (e.g., stepping away from the patient during the exam). Wearing a personnel monitoring badge under the lead apron at the waist will provide reasonable measurements of the radiation equivalent dose to a fetus.

In radiation protection, we constantly emphasize the importance of maintaining radiation exposures "as low as reasonably achievable (ALARA)." Sometimes, there is too much emphasis on "low" and not enough consideration given to what is "reasonable." While it is true that your staff member who thinks she might become pregnant can eliminate the potential exposure to her unborn child by not participating in fluoroscopy procedures at all, is that a "reasonable" approach? A lead apron combined with other typical radiation safety practices, along with proper monitoring with a personnel monitoring badge should meet the ALARA concept, while still allowing that individual to participate in the procedures.

The International Atomic Energy Agency (IAEA) addresses many of these issues in a "question and answer (Q&A)" format. 

The IAEA also provides a document that can be printed out and posted in areas where fluoroscopy is used as a constant reminder of the appropriate radiation safety practices that should be used.

Mack L. Richard, MS, 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 16 April 2012. 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.