A Phase II trial of Higher RadiOtherapy Dose In The Eradication of early rectal cancer.

- Biopsy confirmed adenocarcinoma of the rectum - Age 18 or over - Able to provide written informed consent - MDT deems patient unsuitable for radical TME surgical resection of their tumour either because they are considered to be at increased surgical risk from TME (for example due to general frailty or due to specific co-morbidities which make anaesthetic or surgery hazardous, such as cardiac disease, pulmonary disease, renal failure, previous anaesthetic problems or previous pelvic surgery), or they have marked anxiety at the prospect of a stoma, or because of anticipated difficulty managing a stoma post-operatively (including physical causes such as arthritis, Dupuytren’s contracture and visual problems). - Patient is suitable for either pelvic radiotherapy or chemoradiation in the opinion of the treating oncologist - ECOG PS 0-2 - Primary tumour is < = 4 cm in maximum diameter - Primary tumour is staged at T1-T3b. (TNM staging as per UICC 8th Edition (Appendix B), with additional T3 subdivisions) - Tumour is visible on MRI - Superior aspect of tumour is at or below a horizontal line drawn from the anterior aspect of the S2/3 junction on pre-treatment MRI - No unequivocally involved lymph nodes, i.e. NX (nodes too small to characterise as to say equivocal nodes) and N0 are both eligible - For low rectal tumours superior to the puborectalis sling, patients are eligible if the mesorectal fascia or levator are: o Clear (> 1 mm from disease to levator ani or mesorectal fascia) o or threatened (< = 1mm from disease to levator ani or mesorectal fascia) o or mesorectal fascia is involved but not breached - Estimated creatinine clearance > = 50 mls/min (estimated using a validated creatinine clearance calculation e.g. Cockroft and Gault (Appendix D) or Wright formula) - Absolute neutrophil count > 1.5 x 109/l; platelets > 100 x 109/l - Serum transaminase concentration < 3 x Upper Limit Normal (ULN) - Bilirubin concentration < 1.5 x ULN

- Nodal involvement identified by nodes showing irregular margins and or heterogeneous signal on the high resolution MRI (i.e. N1-N2) - The presence of EMVI discontinuous with the primary tumour - Discontinuous tumour deposits (N1c) - Dominant mucinous tumour on MRI - Signet ring carcinoma or tumours histopathologically containing a neuroendocrine component - Tumour has grown through and breached mesorectal fascia - Tumour involves or breaches the levator ani (as this would be T4b disease) - Involvement of anal intersphincteric plane or external anal sphincter or adjacent organs (If the participant has a low rectal tumour extending inferior to the puborectalis sling, involvement of the internal anal sphincter is permitted) - Undergone an attempt at complete local resection of their cancer - Previous pelvic radiotherapy - Definite distant metastases (equivocal distant metastases on the CT scan are permitted, e.g. indeterminate lung modules, sub-centimetre retroperitoneal nodes or indeterminate liver lesion) - Defunctioning colostomy or ileostomy has been fashioned - Prior invasive malignancy unless disease free for a minimum of 3 years (excluding basal cell carcinoma of the skin or other in situ carcinomas) - Prior systemic chemotherapy for colorectal cancer - Women who are pregnant, breastfeeding or a women of child bearing potential who are unwilling to use effective contraceptive methods