Answer to Question #11188 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Lead Aprons

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


In reviewing your Frequently Asked Questions (FAQs), I read that shields are not required for head computerized tomography (CT) patients due to low levels of scatter. Can you please help me explain why parents of pediatric patients should wear an apron when in the room if the patient is not shielded?


The easiest way to explain this is to think of the CT radiation as "bouncing" off of the patient—this is commonly referred to as "scattered" radiation. Anyone in the CT room during the actual scan would receive some radiation exposure from this scattered radiation. The closer one is to the patient during the CT scan, the higher the scattered radiation exposure would be. While the scattered-radiation exposure to others in the room is very low, many state regulations require that lead aprons be worn by anyone in the CT room during a scan. That practice is also consistent with maintaining radiation exposures to individuals not being scanned as low as reasonably achievable (ALARA).

The situation is a little different for the patient. Any of the scattered radiation mentioned above is bouncing off the patient into the room—it is moving away from the patient. The patient doesn't receive any exposure from this "external" scatter. As such, placing a lead apron on the patient wouldn't be necessary. Other portions of the patient's body do receive some scattered radiation; however, this scattered radiation is "internal" meaning it is from radiation bouncing around inside the patient's body, and of course, we can't place shields inside the body. As with external scatter, the organs closest to the part of the body being scanned receive higher radiation doses than organs that are farther away. That said, this internal scatter drops off very rapidly inside the body, so organs that are more than a few centimeters from the area being scanned receive very little radiation.

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 25 March 2015. 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.