Randomizing Two Radiotherapy Boost Options to Avoid Rectal Cancer Surgery

Inclusion Criteria: * Rectal cancer patients, clinically staged as T2-T3a,b N0-1 by MRI or endoscopic/trans-rectal ultrasound * Rectal cancer staged as N0-1 by MRI or EUS/TRUS * No metastatic lesion * Rectal tumor occupying less than half of the circumference * Tumor less than 5 cm on its largest dimension * Tumor located at less than 10 cm from the anal verge * Tumor penetration less than 5 mm in the mesorectal fat * Tumor accessible for brachytherapy * Lumen accessible for colonoscopy * Patient should be a suitable candidate for brachytherapy and chemotherapy * Older than 18 years of age * Adequate birth control measures in women of childbearing potential * Written informed consent Exclusion Criteria: * Patients with previous pelvic radiation * Evidence of distant metastasis * Extension of malignant disease to the anal canal * Tumors staged as T4 * Tumors larger than 5 cm in length