How long does radiotherapy take to work for rectal cancer?

Radiotherapy may be given before surgery, with chemotherapy, or as part of a plan focused on symptom control. When it is used before an operation, the interval after treatment allows the team to assess the tumour and plan the next step. A smaller tumour on examination or imaging can be helpful, but response is interpreted with the original tumour features and other tests.

Bowel urgency, looser stools, mucus, tiredness or skin soreness can appear during or after treatment. These effects can reflect inflammation in tissues receiving radiation and do not by themselves show whether the cancer is responding.

Attend treatment and surgical planning appointments, and tell the team how often you are opening your bowels, whether you see blood, and whether pain or urgency is limiting daily activities. Ask for advice about fluids, food choices and skin care rather than starting supplements or creams without checking.

Confirm when your examination, scan or endoscopy is planned and how it will affect the next treatment decision. You can read about [Rectal Cancer](/conditions/rectal-cancer/) and [Radiotherapy](/treatments/radiation-oncology/radiotherapy/).

Contact your team promptly for increasing abdominal pain, persistent vomiting, inability to pass stool or gas, fever, dehydration, or more bleeding than you were told to expect. Seek urgent help for severe pain, fainting, heavy bleeding or a swollen abdomen with repeated vomiting.

Ask: Is radiotherapy intended to shrink the tumour before surgery or control symptoms? When will response be assessed? Which test will guide the next step? What bowel changes should I report the same day?