Current surgical treatment for rectal cancer includes total mesorectal excision (TME) which involves excision of the rectum in its encompassing fat including the lymph nodes. Rectal cancer can spread to lymph nodes locally inside the TME 'package' and the lateral pelvic lymph nodes. The TME must be fully excised to ensure that the circumferential resection margin (CRM) is disease free or negative. Despite advancing surgical techniques, a positive margin can occur in around 9% of patients with accurate pre-operative magnetic resonance imaging (MRI), increasing the risk of local recurrence.