Organ Preservation in Rectal Cancer by Dose Escalated MR Guided Adaptive Radiotherapy

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).