Answer to Question #12680 Submitted to "Ask the Experts"

Can you explain how a cardiovascular (CVL) technician or x-ray technician doing fluoroscopic exams can get a beta reading on a film badge? Is this low-energy scatter x rays from the patient that give a false beta reading? What is the best way to address this?

I cannot give a completely definitive answer to your question but can discuss possible relevant considerations. The first thing I would do is to contact the vendor who processes your personnel dosimeters. You should ask the vendor to validate their finding and whether another radiation effect could have accounted for the beta report. 

The next concern I would have is whether this is a routine occurrence or a one-time or rare event? If it is a one-time or rare event, it raises the possibility that the exposure might have been from a radiation source outside of the cardiovascular laboratory or other x-ray work areas. For example, is it possible that the technologist left his/her badge in a location where it might be exposed to beta radiation—e.g., near a radioactive waste storage container or area or in the nuclear medicine laboratory or other facility where beta emitters such as ⁹⁰Sr-⁹⁰Y might have been available?

If you can rule out the possibility of badge exposure outside of the CVL area (or other possible x-ray areas), then other possibilities might have to be investigated. Since you describe your concern as with the CVL or other x-ray areas, all the expected radiation in use would be x rays coming from the machines, and we would not expect any beta-emitting sources to be involved. This means, as you have inferred, that some other effect is causing the misinterpretation of the reading on at least one badge element associated with beta radiation exposure. It is most likely that the vendor used the "skin" element (portion of the film in this case) to interpret the magnitude of the apparent beta dose from the excess response on this element compared to elements lying at greater depths. This element normally lies below a fixed thickness of tissue-equivalent material with a mass density thickness of 7 mg cm^-2, the nominal thickness of the dead skin layer above the active skin cells. You mentioned the possibility of low-energy x rays being a possible cause of the response and subsequent misinterpretation; I believe this is a likelihood.

You state that the specific dosimeter being used was a film badge. Compared to some other common personnel dosimetry media, film has the unfortunate characteristic of being especially light sensitive and, as a consequence, requires packaging in a light-proof fashion. This usually involves wrapping the film in a moderately thick (often > 20 mg cm^-2) light-tight material. The result is that the film under the "beta" window is insensitive to modest energy beta particles (< about 250 keV). This property could possibly result in the film under the beta window exhibiting a response to low-energy photons that would get interpreted as a high-energy beta exposure. The algorithm the vendor uses likely subtracts the film response under a thicker filter element (possibly 300 mg cm^-2 or 1,000 mg cm^-2) from that under the skin dose window (7 mg cm^-2), possibly using an adjusting factor, and if the difference exceeds a particular amount, it is interpreted to represent a beta dose. If you regularly get reported beta doses, I would judge that this kind of interpretative scenario is the likely cause. It is helpful to know what algorithm the vendor uses to interpret beta dose as this may provide some insight as to how the interpretation of beta dose vs. alternative radiation may be made.

Additionally, film, as well as other dosimeter types, use specific badge configurations—e.g., various types of holders and types of filters (different materials and different thicknesses) covering the active dosimeter elements. These can have a variety of effects on responses. For example, the use of certain high atomic number materials can result in excess secondary electron production though enhanced photoelectric interactions, and it is possible that these may be interpreted as beta radiation if they are incident on an active element. Usually this is not a problem because the high atomic number filters are generally associated with deeper dose interpretation, and secondary electrons produced should not have a notable effect on the shallow dose element. High atomic number attenuators may also greatly affect the response to lower energy photons and, again depending on algorithms in use, might affect the vendor's dose interpretation.

While we cannot make an absolute determination of the cause of the reported "beta" doses, I hope the above information is helpful as you attempt to resolve the apparent reporting error. As suggested, speak with your vendor, explaining your position and concern. If you are convinced that no beta exposure occurred, attempt to convince the vendor to reinterpret the doses under the assumption that x rays are the only sources of exposure. I wish you well in your pursuits.

George Chabot, PhD, CHP