Fiducial markers: can the urologist do better?

Radiotherapy to the bladder has a risk of toxicity to pelvic structures, which can be reduced by using fiducial markers for targeting. Injectable contrast offers an alternative marker to gold seeds, which may fall out or exacerbate scarring. Combining contrast agents with tissue glue can minimize dispersion through tissue, enhancing its utility. We evaluated combinations of contrast agents and tissue glue using porcine bladder, for feasibility and utility as fiducial markers to aid image-guided radiotherapy.

Different contrast agents (Lipiodol ultra or Urografin) were combined with different tissue glues (Histoacryl, Tisseal or Glubran2). The mixtures were endoscopically injected into porcine bladder submucosa to identify the area of interest with multiple fiducial markers. The porcine bladders were imaged within a phantom porcine pelvis using standard radiation therapy imaging modalities. The feasibility as an injectable fiducial marker and visibility of each fiducial marker on imaging were scored as binary outcomes by two proceduralists and two radiation therapists, respectively.

Lipiodol-glue combinations were successfully administered as multiple fiducials that were evident on CT and CBCT. Lipiodol with Histoacryl or Glubran2 was visible on kV imaging. The Lipiodol Glubran2 combination was deemed subjectively easiest to use at delivery, and a better fiducial on KV imaging.

This study demonstrates the feasibility of mixing contrast medium Lipiodol with Histoacryl or Glubran2 tissue glue, which, injected endoscopically, provides discrete and visible fiducial markers to aid image-guided radiotherapy. Although promising, further study is required to assess the durability of these markers through a course of radiotherapy.