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Magnetic resonance safety and compatibility of tantalum markers used in proton beam therapy for intraocular tumors: A 7.0 Tesla study
Author(s) -
Oberacker Eva,
Paul Katharina,
Huelnhagen Till,
Oezerdem Celal,
Winter Lukas,
Pohlmann Andreas,
Boehmert Laura,
Stachs Oliver,
Heufelder Jens,
Weber Andreas,
Rehak Matus,
Seibel Ira,
Niendorf Thoralf
Publication year - 2017
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26534
Subject(s) - proton therapy , specific absorption rate , magnetic resonance imaging , nuclear magnetic resonance , nuclear medicine , materials science , optics , biomedical engineering , medicine , physics , radiology , beam (structure) , computer science , antenna (radio) , telecommunications
Purpose Proton radiation therapy (PRT) is a standard treatment of uveal melanoma. PRT patients undergo implantation of ocular tantalum markers (OTMs) for treatment planning. Ultra‐high‐field MRI is a promising technique for 3D tumor visualization and PRT planning. This work examines MR safety and compatibility of OTMs at 7.0 Tesla. Methods MR safety assessment included deflection angle measurements (DAMs), electromagnetic field (EMF) simulations for specific absorption rate (SAR) estimation, and temperature simulations for examining radiofrequency heating using a bow‐tie dipole antenna for transmission. MR compatibility was assessed by susceptibility artifacts in agarose, ex vivo pig eyes, and in an ex vivo tumor eye using gradient echo and fast spin‐echo imaging. Results DAM (α < 1 °) demonstrated no risk attributed to magnetically induced OTM deflection. EMF simulations showed that an OTM can be approximated by a disk, demonstrated the need for averaging masses of m ave = 0.01 g to accommodate the OTM, and provided SAR 0.01g,maximum = 2.64 W/kg (P in = 1W) in OTM presence. A transfer function was derived, enabling SAR 0.01g estimation for individual patient scenarios without the OTM being integrated. Thermal simulations revealed minor OTM‐related temperature increase (δT < 15 mK). Susceptibility artifact size (<8 mm) and location suggest no restrictions for MRI of the nervus opticus. Conclusion OTMs are not a per se contraindication for MRI. Magn Reson Med 78:1533–1546, 2017. © 2016 International Society for Magnetic Resonance in Medicine.