This study is testing whether radiation delivered with MRI guidance using a so-called MR-linac in distal rectal cancer can result in a high rate of organ preservation. Patients will receive radiotherapy together with standard chemotherapy.

Inclusion Criteria:

• Patients with histologically confirmed diagnosis of rectal cancer localized between dentate line and 12 cm from the anocutaneous line

• Any MRI staged rectal cancer meeting the following criteria

• cT1-cT3 and

• cN0 -cN1 and

• cM0

• Inclusion of UICC Stage I tumors only if unsuitable for endoscopic resection or if primary surgery would require permanent colostomy or deep anastomosis with expected poor organ function.

• Tumor affects less than 70% of the rectal circumference.

• Maximum longitudinal extension of the tumor less than 8 cm on MRI

• MR-Staging requirements: High-resolution, thin-sliced (i.e.

  ≤3mm) magnetic resonance imaging (MRI) of the pelvis.

• Cross-sectional imaging of the abdomen and chest to exclude distant metastases.

• Aged at least 18 years. No upper age limit.

• WHO/ECOG Performance Status ≤ 1

• Adequate hematological, hepatic, renal and metabolic function parameters

• Informed consent of the patient

Exclusion Criteria:

• Lower border of the tumor localised more than 12 cm from the anocutaneous line as measured by rigid rectoscopy
• Distant metastases
• Preexisting fecal incontinence for solid stool
• Prior antineoplastic therapy for rectal cancer
• Prior radiotherapy of the pelvic region
• Subject pregnant or breast feeding, or planning to become pregnant within 6 months after the end of treatment.
• Subject (male or female) is not willing to use highly effective methods of contraception (per institutional standard) during treatment and for 6 months (male or female) after the end of treatment (adequate: oral contraceptives, intrauterine device or barrier method in conjunction with spermicidal jelly).
• Other concomitant antineoplastic therapy
• Serious concurrent diseases, including neurologic or psychiatric disorders (incl. dementia and uncontrolled seizures), active,uncontrolled infections, active, disseminated coagulation disorder
• Other primary tumors with an estimated life expectancy of less than three years
• Contraindications for treatment with 5-Fluorouracil or Capecitabine
• Psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule (these conditions should be discussed with the patient before registration in the trial).

Data will be shared if a sound scientific proposal if provided.