Answer to Question #9545 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment and Shielding — Lead Aprons

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

Q

I am a radiographer and have recently been doing some work in a pain clinic whereby using a fluoroscopic C-arm you can screen to show the position of a needle for various procedures (such as nerve root block etc.).

The physician often asks for the C-Arm to be rotated in an oblique manner (i.e., under the table and over, going in an anterior/posterior to a lateral position around the patient's body in a C-arm movement) while screening at the same time.

This has raised some concern with me. To rotate the C-arm means I am very close to the source of the x-ray tube, and more often than not the tube is pointing towards me. As we are usually visualizing the lumbar spine, the factor of scatter is also a concern.

I wear a lead gown and a thyroid protector and, of course, I try and keep far away from the C-arm but my arms are not very long! I am literally 30 cm from the tube.

Should I be concerned? Would you feel comfortable doing this? Should I say something to the physician or just follow his screening orders?

A

If you are wearing a lead apron and thyroid shield, this should adequately protect you.

Besides, for these kinds of procedures the beam-on time is pretty short. You are exposed to x rays only when the beam is on (that is, when the pedal is being pushed).

When you rotate the C-arm, try to stay closer to the image intensifier (and further from the x-ray tube). That will reduce your exposure from scatter radiation from the x-ray tube side of the patient.

The beam is pretty well collimated, but there could be a little exposure.

Remember, most of the dose that you get is from the scatter radiation coming from the patient, not the x-ray tube. So the farther you are from the patient, the less the exposure as well. If you can move two steps back while the pedal is being pushed, that would help. The inverse square law works very well to your benefit in this situation.

Are you wearing a radiation dosimeter? I am not sure what the policy in your institution is, but we typically provide at least a collar badge (radiation dosimeter) to those who are standing by the side of the patient during fluoroscopy. If your deep dose equivalent readings per quarter do not exceed 1.25 millisieverts, you are below 10% of the typical annual dose limit. If they are above 1.25 millisieverts per quarter (deep dose), you should try to increase distance as described above.

Ninni Jacob, CHP
Ken "Duke" Lovins, 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 3 March 2011. 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.