Impact of Bladder Depletion on Mesorectal Movements During Radiotherapy in Rectal Cancer

This trial is assessing how Bladder filling variations and thus mesorectal movements are less when radiotherapy treatment is received with an empty bladder in rectal cancer

Inclusion Criteria: * Histologically confirmed rectal adenocarcinoma * T2 N+ or T3 any N, eligible for radiotherapy or neo-adjuvant radio-chemotherapy treatment in a long course of 25 fractions * Performance Status less or equal to 2 * Male or female 18 Years and older * Creatinine clearance greater than or equal to 50ml/min * Fertile patients must use effective contraception * Written informed consent * Patient must be affiliated to a Social Health Insurance Exclusion Criteria: * Previous treatment with pelvic radiotherapy * Chronic inflammatory bowel disease in flare-up. * Urinary catheterization, urinary diversion or cystectomy * Hip prosthesis * History of prostatectomy, or hysterectomy * Urinary incontinence \> 2 * Pregnant or nursing patient * Persons deprived of their liberty, as well as adults subject to a legal protection measure * Impossibility to submit to the medical follow-up of this clinical trial for geographical, social or psychological reasons