High precision bladder cancer irradiation by integrating a library planning procedure of 6 prospectively generated SIB IMRT plans with image guidance using lipiodol markers

Abstract

Purpose: To increase local control and decrease side effects for urinary bladder cancer patients by integrating a library planning procedure with image guidance using lipiodol markers.

Methods and materials: Twenty patients with T2-T4N0M0 grade 2-3 invasive bladder carcinoma were treated according to an online adaptive protocol. Initially, the gross tumour volume (GTV) was demarcated during cystoscopy by injecting several drops of lipiodol in the submucosa around the tumour. Subsequently two CT scans were acquired with a full bladder and a voided bladder. On both scans, the boost volume (GTV) and the low-risk bladder volume were delineated. Using an interpolation tool, six concomitant boost IMRT plans with increasing bladder volumes were generated. For each fraction the procedure at the treatment unit was as follows: Firstly, a ConeBeam-CT was acquired and based on the amount of bladder filling the best fitting bladder contours and corresponding GTV and IMRT plans were selected. Secondly, the lipiodol markers were registered using the corresponding GTV contours and it was verified that the corresponding 95%-isodose surface covered the entire bladder. Finally, an online setup correction was applied based on this registration and the corresponding treatment plan was irradiated.

Results: The lipiodol markers were very useful in outlining the GTV at the planning CT and for daily setup correction. While the patients strived for a full bladder filling at time of the treatment, this was seldom accomplished. Due to our protocol an appropriate plan with adequate coverage of the PTV and without excessive dose to healthy tissue was delivered every day. The treatment was very well tolerated by all patients. At the end of the treatment no grade 3 urinary or gastro-intestinal toxicity was observed. After a median follow-up of 28 months two local relapses occurred.

Conclusion: Using the library planning approach combined with online image guidance using lipiodol markers, we were able to deliver a highly conformal dose distribution to all bladder cancer patients achieving promising clinical results.