Answer to Question #7820 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Equipment

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

I am an interventional radiological technologist who works in a catheterization laboratory. I work with a cardiologist who believes that by lowering the patient closer to the tube during cases, we are reducing scatter from the x-ray tube. I believe the only thing we are really doing is increasing dose to the patient by reducing distance from the source and that there is no significant amount of scatter from the x-ray tube. I tried looking for anything about radiation safety and table height but was unable to locate any information. Is he correct?

From Wagner and Archer, "keep the patient at a maximum distance from the x-ray tube" because x-ray intensity at the patient's skin surface is decreased as the distance increases. In addition, "keep the image intensifier as close to the patient as possible" because this will minimize the x-ray concentration at the skin surface.

Scatter radiation comes from the patient, is directly proportional to the amount of x ray striking the patient, and is a maximum at a 90-degree angle to the primary x-ray beam. If you move the patient farther away from the x-ray tube, the scatter radiation will decrease because the amount of x ray striking the patient has decreased.

So, in this case, you are correct!

Ken "Duke" Lovins, CHP

Wagner LK, Archer BR. Minimizing risks from fluoroscopic x-rays. Third Ed. Available at:

Answer posted on 14 October 2008. 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.