Page 47 - ARNM-3-2

Advances in Radiotherapy &

Nuclear Medicine

ORIGINAL RESEARCH ARTICLE
Shielding design calculations for a radiotherapy

vault of a 6 and 10-megavoltage medical
linear accelerator operating with or without a

flattening filter

Mostafa M. Elashmawy*
Department of Radiation Protection, Radiation Control Division, Nuclear and Radiological Research
Center, Egyptian Atomic Energy Authority, Cairo, Egypt

Abstract

This study focuses on upgrading the shielding design of a Co-60 radiotherapy unit
to accommodate a linear accelerator operating at 6 and 10 megavoltage, which can
function in both flattening filter (FF) and flattening filter-free (FFF) modes. Shielding
calculations were performed using analytical methods from the National Council on
Radiation Protection and Measurements Report No. 151 and International Atomic
Energy Agency Safety Reports Series No. 47, considering standard (40 patients/day)
and heavy (60 patients/day) workloads. Barrier thicknesses were determined to
ensure the instantaneous dose rate (IDR) behind primary barriers is ≤7.5 µSv/h in
*Corresponding author: FF mode and ≤20 µSv/h in FFF mode, as recommended in the Institute of Physics
Mostafa M. Elashmawy and Engineering in Medicine Report No. 75. Results showed that workload had no
(mostafa_ashmawy2002@yahoo.
com) significant effect on the primary barrier thickness. Moreover, strict adherence to the
IDR criteria increased shielding demands ranging from 11% to 46% while reducing
Citation: Elashmawy MM.
Shielding design calculations for the personal equivalent dose to 1.2 – 13.4% of the dose constraints. This highlights
a radiotherapy vault of a 6 and a potential overdesign that could substantially increase raise construction costs.
10-megavoltage medical linear Therefore, applying the IDR criteria violates the radiation protection principles,
accelerator operating with or without
a flattening filter. Adv Radiother namely, “optimization.” An alternative approach has been proposed to optimally
Nucl Med. 2025;3(2):39-51. use the IDR criteria by including the patient’s transmission factor in the current IDR
doi: 10.36922/ARNM025070007 criteria or by adopting higher values of IDR strictly to verify the shielding efficiency.
Received: February 14, 2025 Higher IDR adoption would result in lower linear accelerator vault costs and more
Revised: March 27, 2025 realistic shielding calculations consistent with operating conditions.
Accepted: April 11, 2025
Keywords: Medical linear accelerator; Radiotherapy; Flattening filter; Shielding
Published online: April 25, 2025
calculations; Instantaneous dose rate; Optimization
Copyright: © 2025 Author(s).
This is an Open-Access article
distributed under the terms of the
Creative Commons Attribution
License, permitting distribution, 1. Introduction
and reproduction in any medium,
provided the original work is Megavoltage (MV) photon beams produced by linear accelerators at various energies
properly cited. are the most commonly used radiation sources in modern radiation oncology and
Publisher’s Note: AccScience radiotherapy. The primary goal in treatment planning is to deliver an appropriate dose
Publishing remains neutral with to the tumor while minimizing exposure to surrounding tissues and organs at risk. This
regard to jurisdictional claims in
published maps and institutional objective has been progressively enhanced using different radiotherapy techniques,
affiliations. such as three-dimensional conformal radiotherapy, intensity-modulated radiotherapy

Volume 3 Issue 2 (2025) 39 doi: 10.36922/ARNM025070007