Fiducial markers are radiopaque implants, typically composed of gold, that aid in the precise and reproducible targeting of tumors. These markers serve as reference points during CT-based planning, including four-dimensional assessment, enabling real-time correction for tumor motion. Initially, fiducial markers were placed intraoperatively or percutaneously under ultrasound (US) or CT guidance. However, endoscopic ultrasound (EUS) offers superior visualization of deep structures in the mediastinum and abdomen while providing a less invasive alternative to surgical placement. EUS-guided fiducial placement has been successfully used for tumors in nearly all gastrointestinal malignancies such as pancreatic, hepatic, esophageal, gastric, and colorectal cancers. Modern fiducials can fit into 22-gauge fine-needle aspiration (FNA) needles and come preloaded in needle carrier devices for easier deployment. Despite increasing evidence supporting the efficacy of EUS-guided fiducial marker placement in gastrointestinal malignancies, there remains a lack of systematic evaluation in large, prospective, randomized trials. Data regarding its feasibility and safety in patients with gastrointestinal cancers undergoing radiation therapy are particularly scarce. Therefore, this study aimed to assess the success rate of EUS-guided fiducial marker placement in these indications within a tertiary hospital setting.

This retrospective, single-center study was conducted at our tertiary hospital and included patients diagnosed with esophageal, rectal, or pancreatic tumors who required fiducial marker placement for image-guided radiation therapy. The study period extended from January 2016 to October 2025. Patients underwent EUS-guided fiducial marker placement using a preloaded 22-gauge EchoTip Ultra Fiducial Needle (Cook Medical, Limerick, Ireland). The primary outcome was the technical success of the procedure, defined as the accurate deployment of fiducial markers at both the proximal and distal margins of the tumor under EUS guidance. Additionally, the occurrence of procedure-related adverse events was assessed. All procedures were performed by experienced endosonographers using standard EUS techniques. Patients were closely monitored post-procedure for potential complications and CT scan and chest xray were used to confirm marker positioning both immediately after placement and at the completion of radiotherapy.

During the study period, a total of 19 patients underwent EUS-guided fiducial marker placement in our endoscopic unit. The mean age was 65.2 ± 9.8 years, and 52% of the patients were male. Of the participants, two had rectal adenocarcinoma, two had esophageal malignancies, and 15 were diagnosed with pancreatic adenocarcinoma. The overall technical success rate of fiducial marker placement was 94.7%, with successful deployment achieved in 18 patients. In one case, the presence of an extensive collateral venous network (cavernoma) prevented the safe placement of fiducial markers. On average, 2.6 ± 1.2 fiducial markers were placed per patient. The mean tumor size was 23 ± 7 mm. No procedure-related complications were observed. At the completion of radiation therapy, imaging confirmed the presence of markers in all patients. 

Our nine-year experience with EUS-guided fiducial marker placement for esophageal, pancreatic, and rectal tumors demonstrates that the procedure is both safe and highly effective, with no reported complications. Fiducial markers remained intact and visible throughout the course of radiation therapy.