Novel Applications of an Injectable Radiopaque Hydrogel Tissue Marker for Management of Thoracic Malignancies

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 similar to 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.