Organ Preservation in Rectal Cancer: Contact X-ray Brachytherapy vs Extending the Waiting Interval and Local Excision

Inclusion Criteria: * histologically verified adenocarcinoma above the dentate line and within 10cm of the anal verge; * neoadjuvant short-course radiotherapy for patients with 1) IRC and delayed response evaluation according to the Dutch national guidelines (cT1-3, cN1-2 lymph nodal status, no involved MRF or cT3c-d, N0-1 lymph nodal status without pres-ence of significant distant metastases) without full dose chemotherapy in the inter-val (e.g. Rapido-scheme) or 2) LARC due to comorbidity or frailty; OR * neoadjuvant long-course radiotherapy (chemoradiation) for patients with 1) LARC according to the Dutch national guidelines (cT4 tumour, cN2 lymph nodal status, lateral lymph node involvement, and/or involved MRF, without the presence of significant distant metastases) or 2) early rectal cancer or IRC and a strong wish for organ preservation; * clinically near-complete response or a small residual tumour mass \<3 cm; * technically feasible to perform both treatment options (contact x-ray brachytherapy or local excision); * age \>18 years; * written informed consent. Exclusion Criteria: * neoadjuvant or induction chemotherapy prior or adjacent to (chemo)radiation, e.g. patients with a Rapido or M1-scheme are not eligible; * radiation dose \>50.4 Gy or boost dose on the primary tumour; * presence of suspicious lymph nodes (yN1/N2) at first response evaluation; * residual tumour ≥ 3cm or over half of the circumference of the rectal lumen; * patients who are unable to undergo contact x-ray brachytherapy or local excision; * patients who cannot tolerate a completion- or salvage-TME because of comorbidity or frailty;