Colorectal cancer is the second most common cause of death from malignant disease in the United Kingdom, with about 20 000 deaths each year. Around one million new cases (9% of all cancers) are diagnosed each year worldwide (CANCER Mondial; www-dep.iarc.fr). As the UK population ages the incidence is predicted to rise.1 At present the only realistic prospect of cure is complete surgical resection of the primary tumour. The restricted anatomical space in the pelvis makes this technically easier to achieve for cancers of the colon than the rectum. Consequently, local recurrence rates after surgery for rectal cancer have been as high as 50%. Local recurrence is a devastating complication as it is invariably fatal even without disseminated disease. Local recurrence can be reduced by two methods—surgical technique and radiotherapy. Currently, radiotherapy is given to most patients even though only a subgroup will benefit. There is increasing interest in the use of preoperative staging to target high risk patients who will benefit most from radiotherapy. …