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 using this technique; 1 patient was treated to a total dose of 65.6 Gy because dose limiting toxicity occurred before dose escalation. 572 CBCTs have been evaluated. Treatment was delivered using small, medium, and large plans in 35%, 52%, and 13% cases respectively. Mean intra-fraction filling was 14 cm³ (SD 16.3, range 0.23-107.9). Mean time between pre- and post-CBCTs was 13 min (SD 2.1, range 9-18). Mean D 98% as assessed on post-radiotherapy CBCT was 98.7% (SD 1.78, range 89.9-100%). At median follow-up of 8 months (range 1-24 months), 18 patients remain alive and disease free. 2 superficial recurrences and 3 deaths from metastatic bladder cancer have occurred. No muscle invasive recurrences have occurred within this cohort. Using this technique one patient has experienced late toxicity (grade 3 cystitis) 5.3 months after radiotherapy (now resolved). Conclusions: IGART using IMRT to delivery a simultaneous integrated tumour boost is feasible with acceptable toxicity. Trial recruitment continues at 70 Gy and will be evaluated in a randomised trial (RAIDER). Clinical trial information: NCT01124682