Background
Radiotherapy (RT: x-ray treatment) is a common anti-cancer treatment that often cures people of their cancer, but can damage the gastrointestinal (digestive) tract and lead to distressing short-term (acute) and long-term (late) gastrointestinal side effects, which can start many months or years after the radiotherapy has finished. These side effects, such as diarrhoea, faecal urgency (a sudden need to pass stool), and faecal incontinence (leakage of stool from the rectum) can damage a person’s quality of life (QoL). We conducted this review to establish whether there are any treatments that can be given to people undergoing pelvic radiotherapy (RT) to reduce gastrointestinal side effects.

Methods
We searched the medical literature up to 2 November 2017 and selected randomised controlled trials (RCTs) of any preventive treatment (intervention) given to people undergoing RT for pelvic cancer (such as bladder, endometrial, cervix, rectum and prostate cancers). We combined data from similar RCTs to provide a summary estimate of the effect of an intervention and made a judgement about how confident (certain) we are of the findings, using established methods (GRADE).

Results
We identified 92 RCTs involving 44 different interventions to reduce RT-related gastrointestinal side effects. These included new methods (RT techniques) and other aspects of delivering RT (lower RT dosages, different bladder volumes, morning or evening RT delivery, injected gels or rectally-inserted balloons (spacers] to protect the rectum, and other options), drugs (aminosalicylates, amifostine, corticosteroids, famotidine, octreotide, magnesium oxide, misoprostol, selenium, sodium butyrate, smectite, sucralfate, superoxide dismutase), and non-drug treatments (different types of diets, glutamine, counselling, green tea, and other options). We found some evidence to show that certain interventions have no role to play in reducing gastrointestinal side effects (particularly glutamine supplements, misoprostol suppositories, oral magnesium oxide and octreotide injections). However, we found little good evidence (moderate or high certainty) to show that any of the options is helpful. The exceptions to this are the evidence on RT techniques, which shows that conformal (modern) RT techniques are better than older RT techniques, and evidence that vaginal brachytherapy (small radioactive balls placed in the vagina) for early endometrial cancer reduces acute gastrointestinal side effects compared with external-beam radiotherapy.

Conclusions
Modern (conformal) RT methods are helpful in reducing RT-related side effects. There is insufficient evidence to robustly support the use of any single drug or non-drug option or other RT delivery device/option to reduce RT-related gastrointestinal effects. More high-quality research is needed.