Answer to Question #11137 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

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


Is there ever any radiation present in the lead that is used to shield x-ray rooms, computerized tomography (CT) scan rooms, and even radiation therapy rooms (linear accelerators)? Our company provides lead shielding materials for these types of applications, and we have always understood that radiation does not remain in the lead EVER. Can you please offer the definitive answer on this for us?


The radiation in rooms used with high-energy radiotherapy accelerators (above 8 MV) can cause some materials to become radioactive. The reference below gives quite a lot of information on that. Lead is not a material that becomes activated significantly in normal usage, even with the high-energy beams; however, some materials that might be in an alloy with the lead can be activated: tungsten, iron, aluminum, and antimony. Aluminum in concrete walls can also become activated. For the most part, the induced radioactivity in shielding from photon beams, the most common type of radiation used in radiotherapy, quickly decays and presents little danger to personnel or patients. When removing lead shielding from the wall of a radiotherapy room used with beams of 8 MV or greater, if the lead is alloyed with antimony, it might be prudent to have a health physicist check the lead for radioactivity before doing the deconstruction.

In rooms for radiotherapy that uses only photon beams below 8 MV, in diagnostic x-ray rooms, or in CT rooms, the lead, alloyed or not, cannot become radioactive, and the lead shielding is completely safe with respect to radiation.

Bruce Thomadsen, CHP

Thomadsen B, Nath R, Bateman FB, Farr J, Glisson C, Islam Mohammad K, LaFrance T, Moore ME, George XX, Yudelev M. Potential hazard due to induced radioactivity secondary to radiotherapy: the report of task group 136 of the American Association of Physicists in Medicine. Health Phys 107(5):442–460; 2014.

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 26 January 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.