• Identification and mitigation...

Treffer: Identification and mitigation of unexplained dose attenuation caused by sub-table water accumulation in an MR-Linac (Elekta Unity).

Title:
Identification and mitigation of unexplained dose attenuation caused by sub-table water accumulation in an MR-Linac (Elekta Unity).
Authors:
Chen J; Academy of Medical Engineering and Translational Medicine, Tianjin University, Tianjin, China.; Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China., Li Y; Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China., An X; Academy of Medical Engineering and Translational Medicine, Tianjin University, Tianjin, China., Li Z; Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China.
Source:
Journal of applied clinical medical physics [J Appl Clin Med Phys] 2026 Jan; Vol. 27 (1), pp. e70441.
Publication Type:
Journal Article
Language:
English
Journal Info:
Publisher: Wiley on behalf of American Association of Physicists in Medicine Country of Publication: United States NLM ID: 101089176 Publication Model: Print Cited Medium: Internet ISSN: 1526-9914 (Electronic) Linking ISSN: 15269914 NLM ISO Abbreviation: J Appl Clin Med Phys Subsets: MEDLINE
Imprint Name(s):
Publication: 2017- : Malden, MA : Wiley on behalf of American Association of Physicists in Medicine
Original Publication: Reston, VA : American College of Medical Physics, c2000-
MeSH Terms:
Magnetic Resonance Imaging*/methods , Radiotherapy Planning, Computer-Assisted*/methods , Quality Assurance, Health Care*/standards , Particle Accelerators*/instrumentation , Water* , Radiotherapy, Intensity-Modulated*/methods , Phantoms, Imaging*, Humans ; Radiotherapy Dosage ; Image Processing, Computer-Assisted/methods
References:
J Appl Clin Med Phys. 2026 Jan;27(1):e70441. (PMID: 41457865)
Med Phys. 2021 May;48(5):e67-e85. (PMID: 33577091)
Front Oncol. 2020 Sep 08;10:1739. (PMID: 33014859)
J Appl Clin Med Phys. 2022 Mar;23(3):e13518. (PMID: 34994101)
Radiother Oncol. 2021 Jan;154:172-178. (PMID: 32976875)
J Appl Clin Med Phys. 2020 Jan;21(1):205-212. (PMID: 31799753)
J Appl Clin Med Phys. 2016 Nov 08;17(6):283-291. (PMID: 27929501)
Clin Transl Radiat Oncol. 2019 Apr 02;18:54-59. (PMID: 31341976)
Radiother Oncol. 2008 Jan;86(1):25-9. (PMID: 18023488)
Phys Med Biol. 2018 Apr 19;63(8):085015. (PMID: 29521280)
Med Phys. 2009 Sep;36(9):4197-212. (PMID: 19810494)
Grant Information:
12475343 National Natural Science Foundation of China; TS004 Collaborative Academic Innovation Project of Shandong Cancer Hospital; ts202408375 Taishan Scholars Program of Shandong Province
Contributed Indexing:
Keywords: MR‐Linac; dose attenuation; elekta unity; environmental control; quality assurance; root cause analysis
Substance Nomenclature:
059QF0KO0R (Water)
Entry Date(s):
Date Created: 20251229 Date Completed: 20251229 Latest Revision: 20260101
Update Code:
20260101
PubMed Central ID:
PMC12745900
DOI:
10.1002/acm2.70441
PMID:
41457865
Database:
MEDLINE

Weitere Informationen

Purpose: To report and investigate a case of significant dose attenuation observed during quality assurance (QA) of an Elekta Unity MR-Linac system, and to elucidate its root cause and solution.
Methods: During a period of abnormal environmental conditions (elevated temperature and humidity), a >20% dose output reduction was detected at a gantry angle of 180°. A comprehensive investigation was undertaken, including dose output measurements at multiple gantry angles, beam quality assessment, mechanical accuracy checks, EPID image analysis, and gamma pass rate analysis using ArcCheck-MR. The source of the attenuation was localized through a process of elimination.
Results: The investigation revealed severe dose attenuation specifically at angles traversing beneath the treatment couch, with a gamma pass rate (3%/3 mm) dropping to 39.1% at 180°. All other system parameters, including MRI quality and mechanical alignments, were within tolerance. Visual inspection after disassembly confirmed the presence of a substantial pool of water beneath the table, estimated to be at least 3.5 cm deep, which acted as an unintended attenuator. The water was attributed to condensation and drainage issues exacerbated by the failed air-conditioning system. Mitigation strategies, including hardware sealing, enhanced drainage, revised maintenance protocols, and the addition of a 180° dose check to daily QA, successfully resolved the issue.
Conclusion: This case highlights a previously unreported and critical failure mode for MR-Linac systems. It underscores the profound impact of environmental control on machine performance and patient safety. Robust HVAC maintenance, proactive monitoring of sub-table areas, and the inclusion of oblique-angle dosimetry in QA routines are essential for all Elekta Unity and similar high-precision radiotherapy systems.
(© 2025 The Author(s). Journal of Applied Clinical Medical Physics published by Wiley Periodicals, LLC on behalf of The American Association of Physicists in Medicine.)