Neoadjuvant chemoradiotherapy with radiation dose escalation with contact x-ray brachytherapy boost or external beam radiotherapy boost for organ preservation in early cT2–cT3 rectal adenocarcinoma (OPERA): a phase 3, randomised controlled trial - Gerard, JP; Barbet, N; Schiappa, R (Lancet Gastroenterol Hepatol, 2023)