Single-Insertion Deployment of Multimodal Fingerprinted Fiducial Markers for Enhanced SBRT Guidance

Abstract Stereotactic body radiotherapy (SBRT) relies on precise tumor targeting, enabled by the use of fiducial markers. However, conventional marker placement through multiple rigid needle insertions presents risks and may cause tracking errors. This paper introduces a novel approach that combines a flexible ARC needle capable of on-demand curved trajectories with a custom-designed deployment tool. The tool enables the sequential placement of multiple markers through a single entry point with feasibility demonstrated in phantoms and in an ex vivo swine liver under computed tomography (CT) imaging. In addition, we explore the design of new multimodal fiducial markers with distinct radiographic fingerprints, visible in CT, fluoroscopy, ultrasound, and magnetic resonance imaging (MRI). A wide range of candidate materials and configurations were tested in liver-mimicking phantoms and ex vivo tissues to assess visibility and artifact generation. Our results demonstrate feasibility and outline a path toward next-generation fiducials and workflows that may reduce insertions and support improved marker distribution. Future work will focus on quantifying performance, optimizing biocompatible designs, and evaluating the benefits under clinically realistic protocols.