Prospective phase 1 study assessing feasibility of IMRT and IGART to deliver simultaneous integrated high-dose tumor boost (up to 70 Gy) for the radical treatment of localized muscle-invasive bladder cancer.

307 Background: Advances in IGART offer individualized solutions to improve target coverage and reduce normal tissue irradiation allowing opportunity to increase radiation tumour dose and spare normal bladder. Methods: A library of 3 IMRT plans were created (small, medium and large) from planning CT scans performed at 30 and 60 minutes; treating whole bladder to 52 Gy and tumour to 70 Gy in 32 fractions. Where normal tissue dose constraints were not met consideration was made to boosting tumour to lower dose (68 Gy-64 Gy). Cone beam CT (CBCT) imaging was performed prior to each fraction. Appropriate PTV was selected from the library for treatment delivery. Post treatment CBCT was acquired weekly in order to assess intra-fraction filling and coverage. Results: 22 patients have been planned using this technique. All have met tissue constraints for treatment to 70 Gy. 21 patients have completed radiotherapy, 18 completed treatment to 70 Gy; 1 patient was planned and treated to 68 Gy prior to dose escalation ...