Inclusion Criteria:  ≥18 years of age and capable of giving informed consent. ycT1-3N0(*) residual(**) histology confirmed rectal adenocarcinoma after neoadjuvant radiotherapy or long-course chemoradiotherapy for which patients will undergo TME surgery. Minimal interval between end of neoadjuvant chemoradiotherapy or radiotherapy: 6 weeks.  (*)= as determined by clinical assessment (digital rectal examination, endoscopy with or without biopsy) and/or MRI. Biopsy/histology around the time of diagnosis is adequate; no biopsy/histology is needed after neoadjuvant therapy.  (**)= including tumor regrowths/local recurrence after an initial clinical complete response and a "watch and wait" approach. These patients will also be included after the local recurrence has been determined using endoscopy and/or MRI.  Exclusion Criteria:  Patient has received brachytherapy as part of neoadjuvant treatment. <18 years of age or incapable of giving informed consent. Patient has not been treated with neoadjuvant radiotherapy or long-course chemoradiotherapy. Patient will not undergo TME surgery for a ycT1-3N0 residual histology confirmed rectal adenocarcinoma. Interval between end of neoadjuvant therapy and surgery is <6 weeks.