In this phase 1 trial, the investigators will prospectively evaluate 3 different external beam radiotherapy (EBRT) schedules. In every schedule, the whole bladder will be treated to 40 Gray (Gy) in 20 fractions, 5 fractions/week, 4 weeks in total. Based on the summation of abnormalities seen on pre- (initial tumor region) and post transurethral resection zone of fibrosis Diffusion weighted-magnetic resonance imaging (MRI) images the tumor region is delineated and defined as a gross tumor volume (GTV). The GTV will be treated using a simultaneous integrated boost (SIB): without extending the 4-weeks treatment period, 3 different dose levels will be implemented in order to increase the biological equivalent dose (BED), as muscle invasive bladder cancer has been shown to be dose-sensitive.

3 different dose levels will be implemented in order to increase the biological equivalent dose (BED), as muscle invasive bladder cancer has been shown to be dose-sensitive.

• Level 1: 57.6 Gray (Gy) (20 x 2.88 Gy, 5 fractions/week, 4 weeks); BED: 61 Gy.
• Level 2: 60 Gy (20 x 3.00 Gy, 5 fractions/week, 4 weeks); BED: 64 Gy
• Level 3: 62.4 Gy (20 x 3.12Gy, 5 fractions/week, 4 weeks); BED: 67 Gy. Fiducials will be implanted at the edges of the postoperative bed during the second transurethral resection of the bladder to improve visualization of the gross tumor volume (GTV) during external beam radiotherapy (EBRT) and consequently improve treatment delivery accuracy. In order to further improve the treatment accuracy, 5 planning Computed Tomographies and plans, with different bladder fillings will be made upfront in our study. During treatment the plan corresponding best with bladder filling at time of EBRT will be selected and delivered.

Inclusion Criteria:

• histological proven diagnosis of muscle invasive bladder cancer
• stage \