A Novel Liquid Fiducial Marker in Esophageal Cancer Image Guided Radiation Therapy: Technical Feasibility and Visibility on Imaging

Purpose: To assess the technical feasibility of injection, visibility on imaging modalities, and positional stability of a novel liquid fiducial marker (ie, BioXmark) for radiation therapy in patients with esophageal cancer. Methods: First, the visibility on imaging of different volumes of the liquid marker was analyzed ex vivo in porcine tissue (ie, on computed tomography [CT], cone beam CT (CBCT), and magnetic resonance imaging [MRI]). Next, for the in vivo part, the liquid fiducial markers were injected under endoscopic (ultrasound) guidance in 10 patients with curable esophageal cancer. The technical feasibility of the injection procedure and the clinical performance (ie, visibility and positional stability on imaging) were evaluated. Planning CT, daily CBCT, and serial MRI images (before, during, and after chemoradiation therapy in a subset of 3 patients) were acquired. Results: Ex vivo, the optimal volume for good visibility without artifacts was 0.1 mL, per injected marker. In vivo, a total of 28 markers were injected in 10 patients (range, 0.025-0.1 ml). No adverse effects were identified. The first 2 cases (4 markers) were considered as learning cases. A total of 19 of 24 of the liquid markers (79%) were visible on CT, 3 of 4 (75%) on MRI, and 19 of 24 (79%) on the first CBCT. All markers with an injected volume of >0.05 mL, were visible on the different imaging modalities. Positional stability analysis on CBCT identified no time trend during the radiation therapy course. No artifacts could be detected for liquid marker volumes of 0.05 and 0.025 mL, in CT or CBCT. Conclusions: Injection of a liquid fiducial marker for esophageal cancer radiation therapy is technically feasible with no adverse events identified. Volumes of >0.05 mL have an appropriate visibility on CT, CBCT, and MRI, with an excellent positional stability. Liquid fiducial markers are therefore promising for use in image guided radiation therapy. (C) 2019 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.