Radiotherapy: how to treat the side effects

Written in association with:

Gastroenterologist

Published: 02/09/2019
Edited by: Laura Burgess

Radiotherapy that targets pelvic cancers may leave patients with secondary problems in the bladder or bowel, which can lead to incontinence, constipation, diarrhoea and cramping. Here, expert gastroenterologist Dr Shameer Mehta explains which complications may arise and how pelvic radiation disease is treated.

What are the possible complications from radiotherapy?

Common secondary syndromes of radiotherapy in cases of treating pelvic cancers are:

Bile salt diarrhoea Small intestinal bacterial overgrowth (SIBO) Pancreatic insufficiency Radiation proctopathy

How are these managed or treated?

Firstly, it is important to go through patients’ symptoms as thoroughly as possible to understand the likeliest causes and the best course of action. Some tests are usually required to look for any secondary syndromes because these can be managed with specific treatments.

Bile salt diarrhoea
Bile salts are substances which travel along the bowel to aid digestion. Radiotherapy can affect the metabolism of these bile salts, leading to diarrhoea. This can be easily treated with medicines called bile salt sequestrants, such as Cholestyramine or Colesevelam.

If you are advised to take these medications, it is best to leave a gap of at least two hours between taking them and taking any other medicines. This is because they can affect how well other medicines are absorbed into the body and therefore how well they work. In addition, reducing the proportion of fat in your diet can help, although this should be done under the supervision of a dietician.

Small intestinal bacterial overgrowth (SIBO)
By changing the environment within the bowel, radiotherapy can cause an overgrowth of harmful bacteria, particularly within the small bowel (or intestine). This part of the bowel is important for the absorption of nutrients and calories with diseases often causing unpleasant symptoms such as diarrhoea, discomfort or bloating.

It is important that the correct breath test is performed to make sure the diagnosis is not missed. Furthermore, an appropriate breath test will tell us if a patient has hydrogen or methane predominant SIBO and provide information on gut transit, which is important for planning treatment.

Treatment consists of antibiotics, probiotics or dietary changes to avoid triggers. Although it is not clear which antibiotic is the best for a specific patient, Rifaximin appears to be the best initial choice for most patients according to scientific trials performed so far. Patients with methane-predominant SIBO may respond better to a combination of Rifaximin and Neomycin.

I often ask patients to follow this up with a course of high-quality probiotics whilst making dietary changes, sometimes under the supervision of a specialist dietician. The FODMAPs diet can be helpful here, by helping patients avoid fermentable carbohydrates and sugars that may be clear triggers for their symptoms. All of these approaches can help to avoid SIBO returning once it is successfully treated.

Pancreatic insufficiency
A proportion of patients with pelvic cancers are treated with radiotherapy to the abdomen as well as the pelvis. In these patients, the pancreas gland may be affected such that the ability to produce and pump helpful digestive enzymes into the gut is reduced. This is called pancreatic exocrine insufficiency. This can be diagnosed using a stool test called a faecal elastase.

Low elastase values may indicate pancreatic exocrine insufficiency. However, it is important that results are interpreted by a professional, as they can be affected by other conditions (e.g. SIBO). Furthermore, abnormal results can be caused by the simple presence of diarrhoea of any cause (the so-called ‘dilutional’ effect).

Pancreatic exocrine insufficiency can be easily treated by adding in these digestive enzymes back into the patient’s diet. These are available in capsule form and are taken with meals to mimic the usual digestive process. Some patients do not respond straight away, which is usually due to the dose not being high enough for them. I also advocate using anti-acid medications to avoid the enzymes being broken down in the stomach. This ensures enough enzymes arrive in the small bowel, where they can aid normal digestion.

Radiation proctopathy
The lower part of the large bowel, the rectum, is commonly affected by pelvic radiotherapy since it is usually located close by. Radiotherapy affects the blood supply to the rectal wall which responds with the formation of new blood vessels. As these newer vessels are more fragile, they are prone to bleeding leading to the condition radiation proctopathy. This is sometimes also (incorrectly) termed radiation proctitis.

Patients will experience bright red bleeding, which can be understandably distressing. It is important, as in any case of rectal bleeding, to seek medical attention to rule out more serious causes.

This is typically done using a camera test (flexible sigmoidoscopy or colonoscopy). This camera test can not only exclude other causes but also confirm the diagnosis of radiation proctopathy as the lining of the rectum has characteristic appearances.

The most important aspect of treatment is to reassure patients that this is not serious and that, over time, bleeding can settle without treatment. In all patients, I would aim to optimise bowel function and to avoid straining by using dietary measures and sometimes simple laxatives. In some patients further treatment is advisable; it is important to discuss the need for treatment with your doctor. One option is the use of a medication called sucralfate, delivered directly to the rectum in the form of an enema. This can be very effective but most patients are unable, or prefer not, to use this strategy long term.

Other therapies include argon plasma coagulation and formalin instillation, both of which are delivered using a camera test of the lower bowel. These can be effective but can sometimes lead to complications. Research is therefore underway to find better techniques that are effective and without the same risk of side effects.

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