title: Liquid fiducial marker applicability in proton therapy of locally advanced lung cancer.
abstract: We investigated the clinical applicability of a novel liquid fiducial marker (LFM) for image-guided pencil beam scanned (PBS) proton therapy (PBSPT) of locally advanced lung cancer (LALC).
  
  
  
  The relative proton stopping power (RSP) of the LFM was calculated and measured. Dose perturbations of the LFM and three solid markers, in a phantom, were measured. PBSPT treatment planning on computer tomography scans of five patients with LALC with the LFM implanted was performed with 1-3 fields.
  
  
  
  The RSP was experimentally determined to be 1.164 for the LFM. Phantom measurements revealed a maximum relative deviation in dose of 4.8% for the LFM in the spread-out Bragg Peak, compared to 12-67% for the solid markers. Using the experimentally determined RSP, the maximum proton range error introduced by the LFM is about 1mm. If the marker was displaced at PBSPT, the maximum dosimetric error was limited to 2 percentage points for 3-field plans.
  
  
  
  The dose perturbations introduced by the LFM were considerably smaller than the solid markers investigated. The RSP of the fiducial marker should be corrected in the treatment planning system to avoid errors. The investigated LFM introduced clinically acceptable dose perturbations for image-guided PBSPT of LALC.
authors.affiliation: Department of Oncology, Section of Radiotherapy, 3994, Rigshospitalet, Copenhagen, Denmark; Niels Bohr Institute, University of Copenhagen, Denmark. Electronic address: per.jonas.scherman.rydhoeg@regionh.dk.
authors.forename: Jonas
authors.initials: J
authors.lastname: Scherman Rydhög
authors.affiliation: Paul Scherrer Institut, Center for Proton Therapy, Switzerland.
authors.forename: Rosalind
authors.initials: R
authors.lastname: Perrin
authors.affiliation: DTU Nanotech, Department of Micro- and Nanotechnology, Center for Nanomedicine and Theranostics, Technical University of Denmark, Kgs. Lyngby, Denmark; Nanovi Radiotherapy A/S, Kgs. Lyngby, Denmark.
authors.forename: Rasmus Irming
authors.initials: RI
authors.lastname: Jølck
authors.affiliation: Paul Scherrer Institut, Center for Proton Therapy, Switzerland.
authors.forename: Francis
authors.initials: F
authors.lastname: Gagnon-Moisan
authors.affiliation: Department of Clinical Medicine, Bispebjerg Hospital, København, Denmark.
authors.forename: Klaus Richter
authors.initials: KR
authors.lastname: Larsen
authors.affiliation: Copenhagen Academy for Medical Education and Simulation (CAMES), Rigshospitalet, Copenhagen, Denmark; Department of Internal Medicine, Zealand University Hospital, Roskilde, Denmark.
authors.forename: Paul
authors.initials: P
authors.lastname: Clementsen
authors.affiliation: Department of Oncology, Section of Radiotherapy, 3994, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Steen
authors.initials: S
authors.lastname: Riisgaard de Blanck
authors.affiliation: Department of Oncology, Section of Radiotherapy, 3994, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Gitte
authors.initials: G
authors.lastname: Fredberg Persson
authors.affiliation: Paul Scherrer Institut, Center for Proton Therapy, Switzerland.
authors.forename: Damien Charles
authors.initials: DC
authors.lastname: Weber
authors.affiliation: Paul Scherrer Institut, Center for Proton Therapy, Switzerland.
authors.forename: Tony
authors.initials: T
authors.lastname: Lomax
authors.affiliation: DTU Nanotech, Department of Micro- and Nanotechnology, Center for Nanomedicine and Theranostics, Technical University of Denmark, Kgs. Lyngby, Denmark.
authors.forename: Thomas Lars
authors.initials: TL
authors.lastname: Andresen
authors.affiliation: Department of Oncology, Section of Radiotherapy, 3994, Rigshospitalet, Copenhagen, Denmark; Niels Bohr Institute, University of Copenhagen, Denmark.
authors.forename: Per
authors.initials: P
authors.lastname: Munck Af Rosenschold
mesh_terms: D057918:Fiducial Markers; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D061766:Proton Therapy / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D014057:Tomography, X-Ray Computed
keywords: Beam perturbation; Liquid fiducial marker; Lung cancer; Proton therapy