A279 A NOVEL TECHNIQUE AND INDICATION FOR EUS-GUIDED FIDUCIAL IMPLANTATION

Luminal gastrointestinal cancers are the fourth most common cause of cancer-related deaths worldwide. Radiotherapy is a mainstay treatment for luminal GI cancers in neoadjuvant, adjuvant, radical, and palliative settings. Placement of fiducials to help guide radiotherapy in pancreatic, breast, and prostate cancer is well established. The role of fiducial implantation in managing gastric cancers is still under investigation. Gastric cancers are often difficult to delineate on CT, therefore fiducial markers can potentially improve the accuracy of tumor target delineation and allow for sparing of nearby uninvolved tissues, optimizing the therapeutic index. This case report outlines a novel technique for EUS-guided fiducial implantation to assist treatment planning CTs (TPCTs) for the improved delivery of image-guided radiotherapy in gastric cancer. A literature review using PUBMED was conducted to help contextualize this novel technique. This case involves a 58-year-old male, ECOG 3 from numerous comorbidities with a T3 gastric adenocarcinoma at the incisura and prominent mediastinal lymph nodes, deemed unfit for surgery or systemic chemotherapy. Under EUS and fluoroscopic guidance, 4 fiducials were implanted submucosally around the inoperable gastric mass found at the incisura using a novel technique. 1.5cc of sterile saline was initially injected submucosally using a 19G FNA needle to create a bleb into which a 3 x 0.7 mm solid platinum fiducial was flushed using 1cc of saline. Following successful implantation, the patient underwent non-contrast-enhanced, free-breathing and 4D treatment planning CT scans to guide radiotherapy. The fiducials were successfully implanted at the margins of the gastric mass under EUS and fluoroscopy guidance. There were no immediate (<24 hours) or delayed (2–21 days) complications. The gastric mass was undetectable on CT scan prior to implantation of the fiducials. On the post-fiducial treatment planning CT, all 4 fiducials were visible, thereby delineating the gastric mass. The fiducials could also be seen on the cone-beam CT scans, which are taken daily prior to treatment and generally have poor soft-tissue resolution. The existing literature on the technical feasibility, safety, and efficacy of EUS-guided fiducial implants in aiding image-guided radiotherapy for gastric cancers is limited. This case report details the technical feasibility of placing fiducials under EUS guidance to delineate a gastric mass, and the potential efficacy of identifying the gastric mass on CT scan post implantation. This case will lay the groundwork for future investigations to explore differences in radiotherapy target volumes and clinical outcomes with EUS-guided fiducial implants. EUS-guided fiducial implants represent a novel technique in the delivery of image-guided radiotherapy for gastric cancers. None