title: Magnetic resonance safety and compatibility of tantalum markers used in proton beam therapy for intraocular tumors: A 7.0 Tesla study.
abstract: 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.
  
  
  
  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.
  
  
  
  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 mave= 0.01 g to accommodate the OTM, and provided SAR0.01g,maximum= 2.64 W/kg (Pin= 1W) in OTM presence. A transfer function was derived, enabling SAR0.01gestimation 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.
  
  
  
  OTMs are not a per se contraindication for MRI. Magn Reson Med 78:1533-1546, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Oberacker
authors.affiliation: Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Paul
authors.affiliation: Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
authors.forename: Till
authors.initials: T
authors.lastname: Huelnhagen
authors.affiliation: Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
authors.forename: Celal
authors.initials: C
authors.lastname: Oezerdem
authors.affiliation: Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
authors.forename: Lukas
authors.initials: L
authors.lastname: Winter
authors.affiliation: Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Pohlmann
authors.affiliation: Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
authors.forename: Laura
authors.initials: L
authors.lastname: Boehmert
authors.affiliation: Department of Ophthalmology, University of Rostock, Rostock, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Stachs
authors.affiliation: Charité-Universitätsmedizin Berlin, BerlinProtonen am HZB, Berlin, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Heufelder
authors.affiliation: Charité-Universitätsmedizin Berlin, BerlinProtonen am HZB, Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Weber
authors.affiliation: Charité-Universitätsmedizin Berlin, Klinik für Augenheilkunde Campus Benjamin Franklin, Berlin, Germany.
authors.forename: Matus
authors.initials: M
authors.lastname: Rehak
authors.affiliation: Charité-Universitätsmedizin Berlin, Klinik für Augenheilkunde Campus Benjamin Franklin, Berlin, Germany.
authors.forename: Ira
authors.initials: I
authors.lastname: Seibel
authors.affiliation: Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.|Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
authors.forename: Thoralf
authors.initials: T
authors.lastname: Niendorf
mesh_terms: D000818:Animals; D006358:Hot Temperature; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008545:Melanoma / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D061214:Patient Safety; D019047:Phantoms, Imaging; D061766:Proton Therapy / Q000379:methods / Q000592:standards*; D013552:Swine; D013635:Tantalum / Q000032:analysis* / Q000737:chemistry; D014604:Uveal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D000098943:Uveal Melanoma
chemical_list: D013635:Tantalum
keywords: magnetic resonance imaging; ophthalmic imaging; proton therapy; ultra-high-field MR; uveal melanoma