Iranian Journal of Medical Physics

Iranian Journal of Medical Physics

Assessment of Neutron Contamination in Small Fields of Elekta Synergy Linac in High Energy Photon Beams

Document Type : Original Paper

Authors
Zahra Poshtekeshi 1
Abbas Haghparast 1
Mahdi Ghorbani 2
Hedieh Ranji 3
Meysam Tavakoli 4
1 Department of Medical Physics, Faculty of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran
2 Medical Physics Department, Faculty of Medicine, Mashhad University of Medical Sciences
3 Biomedical Engineering and Medical Physics Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
4 Department of Radiation Oncology, Winship Cancer Institute, Emory University, Atlanta, GA, United States of America
10.22038/ijmp.2026.95945.2696
Abstract
Introduction: Since technique such as intensity-modulated radiation therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) use small fields (< 5 × 5 cm²), data on neutron contamination in such conditions remain limited. This study evaluated neutron dose equivalent (NDE) levels in small fields in 10 MV and 18 MV photon beam energies for Elekta synergy linac.
Material and Methods: Fast NDE were measured by using CR-39 detectors, calibrated with a ²⁴¹Am-Be neutron source. Measurements were conducted at five field sizes (1 × 1 to 5 × 5 cm²) in both 10 MV and 18 MV energies, at the isocenter that was aligned with the center of the field, 5 cm and 10 cm distances from the field edge, and at dmax in a SP34 solid water phantom (Scanditronix-Welhofer, Germany).
Results: The highest NDE (8.18 mSv/Gy) occurred at the isocenter (center of the field) for a 1 × 1 cm² field in 18 MV- five times higher than that for a 5 × 5 cm² field. NDE at dmax was lower by ~88% at the center of the field, and by ~90% at 10 cm from the field edge compared to the center of the field for a 1 × 1 cm2 field in 18 MV energy.
Conclusion: NDE increased with decreasing field sizes, at 10 MV and 18 MV energies. This effect should be considered in treatment planning for techniques that use small fields, due to its potential biological risks.
Keywords
Radiotherapy Medical Linear Accelerator Neutron Contamination CR
39 Small Field Elekta Synergy
Subjects
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Iranian Journal of Medical Physics
Volume 23, Issue 3 - Serial Number 3
May and June 2026
Pages 199-208