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;