EUS-guided fiducial marker placement for radiotherapy in rectal cancer: feasibility of two placement strategies and four fiducial types

Abstract

Background and study aims To facilitate image guidance during radiotherapy of rectal cancer, we investigated the feasibility of fiducial marker placement. This study aimed to evaluate technical success rate and safety of two endoscopic ultrasound (EUS)-guided placement strategies and four fiducial types for rectal cancer patients. Patients and methods This prospective multicenter study included 20 participants who were scheduled to undergo rectal cancer treatment with neoadjuvant short-course radiotherapy or chemoradiation. EUS-guided endoscopy was used for fiducial placement at the tumor site (n = 10) or in the mesorectal fat and in the tumor (n = 10). Four fiducial types were used (Visicoil 0.75 mm, Visicoil 0.50 mm, Cook, Gold Anchor). The endpoints were technical success rate and retention of fiducials, the latter of which was evaluated on cone-beam computed tomography scans during the first five radiotherapy fractions. Results A total of 64 fiducials were placed in 20 patients. For each fiducial type, at least three fiducials were successfully placed in all patients. Technical failure consisted of fiducial blockage within the needle (n = 2) and ejection of two preloaded fiducials at once (n = 4). No serious adverse events were reported. In three patients, one of the fiducials was misplaced without clinical consequences; two in the prostate and one in the intraperitoneal cavity. After a median time of 17 days after placement (range 7 – 47 days), a total of 42/64 (66 %) fiducials were still present (24/44 intratumoral vs. 18/20 mesorectal fiducials, P = 0.009). Conclusions Placement of fiducials in rectal cancer patients is feasible, however, retention rates for intratumoral fiducials were lower (55 %) than for mesorectal fiducials (90 %).

Feasibility of Gold Fiducial Markers as a Surrogate for Gross Tumor Volume Position in Image-Guided Radiation Therapy of Rectal Cancer

“…Previous studies on fiducial insertion in the rectum report no serious adverse events. 22,24,25 In one study, a small amount of bleeding that resolved spontaneously was reported in 1 out of 54 patients. 23 A limitation of this study is the small number of patients.…”

“…In our study, a total of 64 fiducials were inserted, of which 35 fiducials were still in situ at the end of radiation therapy. 24 Furthermore, the insertion of fiducials is an invasive procedure. Previous studies on fiducial insertion in the rectum report no serious adverse events.…”

“…We endoscopically placed the fiducials in the tumor and mesorectum at least 1 day before the start of radiation therapy. The fiducial insertion strategy is described in Rigter et al 24…”

“…The fiducial retention in the REMARK study was described earlier. 24 A total of 35 fiducials in situ were available for analysis on CBCT, of which 26 fiducials were in the tumor and 9 were in the mesorectum. 27 The consensus meeting resulted in 22 identified fiducials on the first MRI and 17 identified fiducials on the second MRI.…”

“…Given that fiducial markers have been proven useful for setup correction in other tumor locations such as pancreas, esophagus, and prostate, [19][20][21] fiducials may be useful as a surrogate for GTV position in rectal cancer. Several studies have reported on the use of fiducials in the rectum and focus on marker visibility and migration, 22 fiducial retention and adverse events, 23,24 and the use of fiducials to aid in the delineation of the target volume. 25 However, none have investigated the potential benefit of fiducials for setup correction in radiation therapy of rectal cancer.…”