Feasibility of the Maastro Applicator in Rectal Cancer

Inclusion Criteria: * ≥ 18 years of age and capable of giving informed consent. * Adenocarcinoma of the rectum classified cT (clinical Tumor) 2-3b, \< 5 cm largest diameter and \< ½ circumference (MRI staging), N0-N1 (any node \< 8 mm diameter), M0 * Operable patient * Tumor accessible to the Maastro applicator with a distance from the lower tumor border to the anal verge ≤10 cm * No comorbidity preventing treatment * Adequate birth control for women of child-bearing potential * Follow-up possible. Exclusion Criteria: * Tumor extending into the anal canal. * Stop of anti-coagulants (except ≤100 mg aspirin/day) is medically contraindicated. * Presence of coagulation disorder resulting in an increased bleeding risk. * Prior pelvic radiation therapy (excluding the abovementioned neoadjuvant treatment). * Prior surgery or chemotherapy for rectal cancer (excluding the abovementioned neoadjuvant treatment). * Inflammatory bowel disease (IBD). * (Systemic) treatment possibly causing rectal or genitourinary toxicity for a separate active malignancy. * World Health Organization performance status (WHO-PS) ≥ 3. * Life expectancy of \< 6 months. * Pregnant women.