External Beam Radiotherapy Combined With Endorectal High-dose-rate Brachytherapy in Elderly and Frail Patients With Rectal Cancer

Inclusion Criteria: * Elderly patients (age ≥70 years) with a G8-frailty score ≤ 14 based on the G8 geriatric assessment tool of frailty and/or elderly patients (age ≥70 years) with American Society of Anesthesiologists Physical Status (ASA PS) ≥ 3 and/ elderly patients (age ≥70 years) unsuitable to tolerate radical surgery as judged by the surgeon and/or elderly patients (age ≥70 years) that refuse radical surgery * Life expectancy ≥ 6 months * Male and female patients with histologically confirmed diagnosis of rectal adenocarcinoma localized 0-16 cm from the anocutaneous line as measured by rigid rectoscopy * MRI-defined cT1-3d N0/+ M0, mrCRM - / +, \</= 2/3 involvement of the rectal wall circumference * Staging requirements: High-resolution, thin-sliced (i.e. 3mm) magnetic resonance imaging (MRI) of the pelvis is the mandatory local staging procedure. * Spiral-CT of the abdomen and chest to exclude distant metastases. Exclusion Criteria: * Previous or current drug abuse * Other concomitant antineoplastic therapy * Prior or concurrent malignancy ≤ 3 years prior to enrolment in study (Exception: non-melanoma skin cancer or cervical carcinoma FIGO stage 0- 1), unless the patient is continuously disease-free * 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).