External Beam Radiotherapy for Muscle Invasive Bladder Cancer

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.