Organ Preservation in Locally Advanced Rectal Cancer by Radiochemotherapy Followed by Consolidation Chemotherapy.

Inclusion Criteria: * Male and female patients with histologically confirmed diagnosis of rectal cancer localized 0 - 12 cm from the anocutaneous line as measured by rigid rectoscopy (i.e. lower and middle third of the rectum) * Any MRI staged cT3 tumor or any cT1 cN+ or cT2 cN+ with nodal staging according to "SOP MRI" * Staging requirements: High-resolution, thin-sliced (i.e. 3mm) magnetic resonance imaging (MRI) of the pelvis is the mandatory local staging procedure. * 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 * cT4 tumors * Positive lateral pelvic lymph nodes * Distant metastases (to be excluded by CT scan of the thorax and abdomen) * Preexisting fecal incontinence for solid stool * Preexisting peripheral sensory neuropathy with functional impairment * Preexisting myelosuppression reflected by a neutrophil count \< 2.000/mm\^3 and/or platelets \< 100.000/mm\^3 * Severe impairment of kidney function with a Creatinin Clearance \< 30 ml/min) * Prior antineoplastic therapy for rectal cancer * Prior radiotherapy of the pelvic region * Major surgery within the last 4 weeks prior to inclusion * 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 according to the "Clinical trial fertility group" * On-treatment participation in an interventional clinical study in the period 30 days prior to inclusion * Previous or current drug abuse * Other concomitant antineoplastic therapy * Serious concurrent diseases, including neurologic or psychiatric disorders (incl. dementia and uncontrolled seizures), active, uncontrolled infections, active, disseminated coagulation disorder, severe liver function disorders * WHO/ECOG Performance Status \> 1 * Clinically significant cardiovascular disease (incl. myocardial infarction, unstable angina, symptomatic congestive heart failure, serious uncontrolled cardiac arrhythmia) ≤ 6 months before enrolment. * Chronic diarrhea (\> grade 1 according NCI CTCAE) Prior or concurrent malignancy ≤ 3 years prior to enrolment in study (Exception: non-melanoma skin cancer or cervical carcinoma FIGO stage 0-1), if the patient is continuously disease-free * Known allergic reactions on study medication * Known dihydropyrimidine dehydrogenase deficiency * Medication inhibitors of the dihydropyrimidine dehydrogenase, such as Brivudin, Sorivudin and its analogues. * Pernicious anemia or other anemias caused by Vitamin B-12 deficiency. * 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). * Additionally for hyperthermia cardiac pacemakers and metal implants in the proximity of the pelvis constitute a criterion for exclusion.