Standard Dose Versus High Dose of Radiotherapy in Rectal Preservation With Chemo-radiotherapy in Rectal Cancer Patients

Inclusion Criteria: * Histopathologically verified adenocarcinoma of the rectum * MDT conference finds patient a candidate for rectal resection * Clinical tumor category cT1-3 * MRI findings * Maximal cross-sectional size of 4.5 cm (axial plane relative to the rectum) * Lowest edge of tumor located at or below the peritoneal reflection on MRI * Performance status 0-2 * Age ≥ 18 years * Eligible for radiotherapy and capecitabine according to investigator, including * Adequate function of bone marrow (neutrophils ≥ 1.5 x 10\^9/l and thrombocytes ≥ 100 x 10\^9/l) * Adequate function of liver (ALAT \< 2.5 x upper limit of normal, bilirubin \< 2.5 x upper limit of normal) * Adequate kidney function (Serum creatinine \< 1.5 x upper limit of normal or measured GFR \> 30 ml/min) * Fertile women must present a negative pregnancy test and use secure contraceptives during and three months after treatment * Written and orally informed consent Exclusion Criteria: * Previous surgical treatment of the present cancer, including transanal excision of tumor * Other malignant disease within the past five years except non-melanoma skin cancer and premalignant lesions such as carcinoma in situ * Distant metastases verified by imaging or biopsy, i.e. cM1 * Previous radiation treatment of the pelvis * Pregnant or breastfeeding women. * Existing colostomy or ileostomy