Role and technique of endoscopic ultrasound placement of fiducial markers in gastrointestinal malignancies

Stereotactic body radiation therapy may be used in the neoadjuvant, adjuvant, or palliative treatment of multiple cancers. Fiducials serve as radiographic reference points for real-time dynamic tracking and accurate radiation delivery. Endoscopic ultrasound with real-time Doppler imaging is a safe minimally invasive approach for fiducial implantation in lesions both within and adjacent to the gastrointestinal lumen. The decision to incorporate image-guided radiotherapy and specifics regarding fiducials and their use in a patient's treatment plan depends on the multidisciplinary collaboration between gastroenterologists, radiation oncologists, medical oncologists, and surgical oncologists. This article will review the indications, controversies in timing, and use of endoscopic ultrasound-guided fiducial placement, the various types of fiducial markers, delivery systems, and deployment techniques available. Also covered will be associated technical and clinical success rates, in addition to previously reported complications.