Safety of a Boost (CXB or EBRT) in Combination With Neoadjuvant Chemoradiotherapy for Early Rectal Adenocarcinoma

The investigators propose to conduct a randomised study on cT2, cT3a-b tumours less than 5 cm using two different techniques of radiotherapy boost following neoadjuvant chemoradiotherapy (nCRT) (CAP45): EBRT (9 Gy/5 fractions) or CXB (90 Gy/3 fractions). The endpoint will be organ preservation at 3 years without non-salvageable local pelvic recurrence. The proof of this concept will be of most benefit for all patients but especially for the elderly who usually are not fit for or keen to undergo major surgery. The hypothesis of this study is to determine whether the addition of an endocavitary boost with CXB after standard treatment with nCRT, increases the chance of rectum and anus preservation by 20%-unites in early rectal adenocarcinoma without locally progressive disease (organ preservation in control arm 20%, in experimental arm 40%). Main objective To demonstrate that neoadjuvant chemoradiotherapy in combination with a boost given with CXB (Arm B) is superior to the same neoadjuvant therapy plus a boost with EBRT alone (Arm A) in terms of rectum (organ) preservation without non salvageable local disease at 3 years post treatment start, or permanent deviating stoma. Study Design Open-label, phase III, prospective, multi-centre, international, randomised 1:1, 2 arm study designed to evaluate the efficacy of a CXB boost versus an EBRT boost.