Inclusion Criteria:- histologically proven rectal adenocarcinoma  no distant metastases on CT scan (M0 disease)  at least one high risk factor for disease recurrence identified on MR imaging:  T4 tumor (cT4) N2 disease (cN2) extramural venous invasion (cEMVI+) positive lateral lymph nodes distance of tumor to mesorectal fascia or positive lymph nodes is 1 mm or less (cMRF+) capacity for informed consent willingness to attend regular check-ups during and after treatment  Exclusion Criteria:history of previous irradiation in the pelvic area  absolute contraindications for MR imaging distant metastases cannot be reliably excluded synchronous cancer chronic inflammatory bowel disease