Assessment of Response Before, During and After Neoadjuvant Chemoradiotherapy in Rectal Cancer Patients

Inclusion Criteria: * Patient is at least 18 years of age. * Patient's body weight is ≤ 120 kg. * Histologically proven and evaluable (according to RECIST criteria) adenocarcinoma of the rectum (tumour \<15 cm from the anal verge), staged T3-4 N0 and T1-4N1-2. * WHO PS ≤ 2 * Adequate bone marrow, hepatic and renal function (assessed within 14 days prior to study entry): * Hemoglobin \>10.0 g/dL, * Absolute neutrophil count \> 1.5 x 109/L, * Platelet count \> 100 x 109/L, * Presence of adequate contraception in fertile patients. Adequate methods of contraception are: intra-uterine device, hormonal contraception, condom use with spermicide. * Written informed consent must be given according to ICH/GCP and national/local regulations. Exclusion Criteria: * Evidence of distant metastases. * Prior chemotherapy or radiotherapy for rectal cancer. * Pregnant or breastfeeding women. * Significant impairment of intestinal resorption (e.g. chronic diarrhea, inflammatory bowel disease). * Known allergies to intravenous contrast agents. * Contra-indications for magnetic resonance imaging (metal implants, claustrophobia, etc. ). * Previous or concurrent malignancies at other sites with the exception of surgically cured or adequately treated carcinoma in-situ of the cervix and non-melanoma skin cancer. * History of uncontrolled seizures, central nervous system disorders or psychiatric disability judged by the investigator to be clinically significant precluding informed consent or interfering with compliance for oral drug intake. * Presence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule; those conditions should be discussed with the patient before registration in the trial.