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28 August 2008

Answer to Question #5354 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

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

Would multileaf collimators be considered as part of a shielding device for radiotherapy accelerators, because not all "shieldings" have to be "physical shields"?

The shielding for accelerators is based on the energy, type of emission (photons, electrons, etc.), and beam size. It is designed to accommodate the maximum beam size. Therefore the use of multileaf collimators is irrelevant to the determination of shielding for protection of workers and the public. Collimation, including multileaf collimation, is important in shaping the beam and protecting the patient from unnecessary levels of radiation in normal tissue surrounding the site to be treated.
For more information, the National Council on Radiation Protection and Measurements (NCRP) has recently published a report, "Structural Shielding Design and Evaluation for Megavoltage X- and Gamma-Ray Radiotherapy Facilities" (Report No. 151). You may view information about the report online.

Ruth McBurney, CHP

Answer posted on 19 April 2006. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of 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 specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.