The feasibility and utility of cystoscopy-guided hydrogel marker placement in patients with muscle invasive bladder cancer

Abstract Background Fiducial markers at the borders of bladder tumors are useful to facilitate target delineation radiotherapy (RT) and offer the possibility of image-guided radiotherapy (IGRT) for a focal boost. Purpose To evaluate the feasibility and technical performance of cystoscopy-guided placement of hydrogel markers in patients with bladder cancer referred for RT. Materials and methods Prospective, multi-center, 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. CT scans and cone-beam CT scans (CBCT) acquired during radiotherapy 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 thirty-two 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% was visible on the Cone beam CT scan (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. Conclusion 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.