title: Novel applications of an injectable radiopaque hydrogel tissue marker for management of thoracic malignancies.
abstract: BACKGROUND
  Radiopaque markers (otherwise known as fiducials) are used clinically to mark sites of biopsy or resection, which aids with targeting of local therapy, including surgery and radiation therapy. We performed a human cadaveric imaging series with a novel, injectable, radiopaque, absorbable hydrogel marker to demonstrate its potential in the management of thoracic malignancies.
  
  
  METHODS
  Baseline CT imaging was performed on three unfixed cadaveric specimens. Hydrogel marker implants were placed in the submucosa of the esophagus, the mediastinum, and lung parenchyma by an endoscopic approach with real-time endobronchial and esophageal ultrasound guidance. Subpleural implants in peripheral lung parenchyma were also performed through an anterolateral thoracotomy. Postimplant simulation CT imaging, T2-weighted MRI, and cone-beam CT imaging were performed. Gross dissection of the lung parenchyma was used to evaluate localization of the hydrogel.
  
  
  RESULTS
  Transthoracic and endoscopic marker placement was readily achieved. The hydrogel appeared hyperechoic by ultrasound, hyperenhancing on T2-weighted MRI, and demonstrated radiopacity of ~300 Hounsfield Units in simulation CT imaging and cone-beam CT imaging. Gross dissection of the lung revealed well-localized blebs of hydrogel marker within lung parenchyma.
  
  
  CONCLUSIONS
  This cadaveric series demonstrates the excellent visibility of a radiopaque injectable hydrogel marker in the human thorax by multiple common imaging techniques. The hydrogel marker forms a well-localized bleb within tissue, which can assist with triangulation of disease during minimally invasive thoracic surgery. Esophageal applications include radiographic delineation of tumor defined by endoscopy and image guidance for radiotherapy. Future in vivo studies are warranted because radiopaque injectable compounds are promising alternatives to metal fiducials.
authors.affiliation: Department of Radiation Oncology and Molecular Sciences, Johns Hopkins University, Baltimore, MD. Electronic address: sde3@jhmi.edu.
authors.forename: Lana
authors.initials: L
authors.lastname: de Souza Lawrence
authors.affiliation: Department of Radiation Oncology and Molecular Sciences, Johns Hopkins University, Baltimore, MD.
authors.forename: Eric
authors.initials: E
authors.lastname: Ford
authors.affiliation: Department of Interventional Pulmonology, Johns Hopkins University, Baltimore, MD.
authors.forename: Christopher
authors.initials: C
authors.lastname: Gilbert
authors.affiliation: Department of Interventional Pulmonology, Johns Hopkins University, Baltimore, MD.
authors.forename: Lonny
authors.initials: L
authors.lastname: Yarmus
authors.affiliation: Department of Thoracic Surgery, Johns Hopkins University, Baltimore, MD.
authors.forename: Avedis
authors.initials: A
authors.lastname: Meneshian
authors.affiliation: Department of Interventional Pulmonology, Johns Hopkins University, Baltimore, MD.
authors.forename: David
authors.initials: D
authors.lastname: Feller-Kopman
authors.affiliation: Department of Radiation Oncology and Molecular Sciences, Johns Hopkins University, Baltimore, MD.
authors.forename: Russell
authors.initials: R
authors.lastname: Hales
mesh_terms: D002102:Cadaver; D054893:Cone-Beam Computed Tomography; D004947:Esophagus / Q000033:anatomy & histology*; D057918:Fiducial Markers; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000008:administration & dosage*; D007267:Injections; D008168:Lung / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging; D008482:Mediastinum / Q000033:anatomy & histology*; D014057:Tomography, X-Ray Computed; D018084:Ultrasonography, Interventional
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate