Rectal adenocarcinoma is rather radioresistant and the dose required to achieve 50% sterilization is close to 90 grays (Gy), which is a high dose causing toxicities when given with external beam radiation therapy (EBRT). Among the radiotherapy techniques able to achieve safely such a high dose, Contact X-Ray Brachytherapy 50 Kv (CXB) is an appealing method.