MRI-based contouring of functional sub-structures of the lower urinary tract in gynaecological radiotherapy

•There are no common guidelines for lower urinary tract contouring in pelvic radiotherapy.•The main bladder substructures involved in morbidity are: bladder wall, trigone, bladder neck and urethra.•Comparison between MRIs for brachytherapy and EBRT showed that the trigone remains stable during treatment.•The length of the urethra is influenced by different treatment conditions.•New dose points and reference dimensions are suggested for gynecological radiotherapy.