Fiducial markers: can the urologist do better?

INTRODUCTION: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Towards individualised radiotherapy for Stage I seminoma.

BACKGROUND AND PURPOSE: Adjuvant radiotherapy is currently standard treatment of Stage I seminoma (SOS). The use of computerised tomogram (CT) planning is compared with traditional planning for greater treatment individualisation. MATERIAL AND METHODS: Two plans were generated for each of 10 patients: one using traditional rectangular para-aortic fields, and one using conformal fields. The primary target volume compared was the dosimetric coverage of the inferior vena cava and aorta. RESULTS: The dosimetric analysis of traditional plans showed that they provided reasonable dosimetric coverage of the CTV. However, if 1cm is used for uncertainty based on nodal coverage then the periphery of the PTV could be significantly under-dosed. The CT based plan delivered improved dosimetry to the vessel PTV compared with the traditional field (CT D 95=24.7 Gy, traditional D 95=23.6 Gy, P=0.002). CT-based plans were significantly wider than traditional plans (CT=11.8 cm, traditional=9 cm, P=0.002). The CT plan tended to irradiate relatively small volumes of the kidneys to higher doses. CONCLUSIONS: Traditional para-aortic fields may deliver suboptimal dosimetry to an anatomically defined PTV. Our CT-based fields tend to be wider than traditional fields, and provide improved dosimetry to vessels based target volumes. Given that traditional fields are often delivering significantly less than the prescribed dose to the target volume, and that marginal relapses cause a high proportion of treatment failure, there is a suggestion that CT-based plans may avoid under-dosage and geographical miss sometimes seen with traditional plans.