The Feasibility and Utility of Cystoscopy-Guided Hydrogel Marker Placement in Patients With Muscle-Invasive Bladder Cancer.

Purpose: Fiducial markers at the borders of bladder tumors are useful to facilitate target delineation radiation therapy (RT) and offer the possibility of image guided RT for a focal boost. Our purpose was to evaluate the feasibility and technical performance of cystoscopy-guided placement of hydrogel markers in patients with bladder cancer referred for RT.

Methods And Materials: Ours was a prospective, multicenter, feasibility, and utility study. Thirty-two consecutive patients with muscle-invasive bladder cancer, referred for RT, underwent cystoscopy-guided implantation of hydrogel markers. Feasibility, clinical performance of the markers, and adverse events were registered. Computer tomography (CT) scans and cone beam CT (CBCT) scans acquired during RT were analyzed to evaluate the visibility and stability of the markers during the radiation period.

Results: A total of 107 hydrogel spots were implanted in 32 patients with bladder cancer. There were no procedure-related adverse events. On the simulation CT scan 76.6% of the implanted markers were sufficient for tumor delineation. At start of treatment 52.3% were visible on the CBCT and adequate for positional verification on a routine basis. The washout rate during treatment was 9.3%. At the end of treatment 46.7% of implanted spots were visible on CBCT scan and adequate for routine positional verification. At patient level, in 31.2% of cases, use of hydrogel fiducials showed adequate performance throughout the whole course.

Conclusions: Cystoscopy-guided placement of hydrogel markers is both safe and feasible for muscle-invasive bladder tumors. Adequate performance for radiation purposes throughout the whole course (implantation, delineation, and positional verification) was 46.7% of all implanted markers, leaving room for improvement.