655 Background: Rectal cancer affects over 40,000 patients in the US per year. The current standard of care for patients with localized rectal cancer is neoadjuvant radiation therapy with concurrent chemotherapy (NCRT) followed by surgery; however, it has shown no proven survival benefit for locally advanced rectal cancer patients. Preliminary results show that a short course of radiation therapy, using high-dose rate endorectal brachytherapy (Endo-HDR), may be as effective with less toxicity and delay to time of surgery. This requires the placement of fiducial markers, using an endoscopic ultrasound guided method (EUS), into the tumor for accurate source placement and treatment. Our aim is to compare three different types of fiducials in terms of visibility and migration. Methods: 12 patients with locally advanced rectal cancer that received Endo-HDR and EUS guided fiducial placement were retrospectively evaluated at JHH. Results: 12 patients underwent EUS guided placement of 42 fiducials. For 11 of our 12 patients, the mean number of fiducials placed per patient was 3.63 (SD 1.03) using a 19-gauge needle. One patient received 2 fiducials using a 22- gauge needle. Of the 12 patients that received fiducials, 3 received traditional fiducials (TF), 8 received segmented fiducials (SF) and 1 received foldable fiducials. All fiducials were clearly visible. The mean number of fiducials that detached from implanted site before surgery for patients with TFs was 0.667, and for patients with SFs was 0.875 (p=0.744). The median migration distance, as measured by interfiduciary distance, for segmented fiducials was significantly larger when compared to traditional fiducials (0.45 cm for SF compared to 0.1 cm for TF; p=0.049) Conclusions: SFs appear to be less stable, with regards to migration, in the rectum when compared to traditional fiducials in our patient population. These differences could be due to placement difficulty or operator dependent differences. Improvement in fiducial structure is required in order to help decrease migration and detachment and maximize visualization, which will lead to more accurate administration of Endo-HDR.
Neoadjuvant chemoradiation alters biomarkers of anticancer immunotherapy responses in locally advanced rectal cancer