The impact of pelvic radiotherapy on the gut microbiome and its role in radiation-induced diarrhoea: a systematic review

Abstract

Pelvic radiotherapy is the key treatment for pelvic malignancies, usually including pelvic primary tumour lesions and lymphatic drainage areas in the pelvic region. Therefore, the intestinal tract in the radiation field is inevitably damaged, a phenomenon clinically referred to as radiation enteritis, and diarrhoea is the most common clinical symptom of radiation enteritis. Therefore, it is necessary to study the mechanism of radiation-induced diarrhoea. It has been found that the gut microbiome plays an important role in the development of diarrhoea in response to pelvic radiotherapy, and the species and distribution of intestinal microbiota are significantly altered in patients after pelvic radiotherapy. In this study, we searched for articles indexed in the Cochrane Library, Web of Science, EMBASE and PubMed databases in English and CNKI, Wanfang data and SINOMED in Chinese from their inception dates through 13 March 2020 to collect studies on the gut microbiome in pelvic radiotherapy patients. Eventually, we included eight studies: one study report on prostatic carcinoma, five studies on gynaecological carcinoma and two papers on pelvic carcinomas. All studies were designed as self-controlled studies, except for one that compared toxicity to nontoxicity. The results from all the studies showed that the diversity of intestinal flora decreased during and after pelvic radiotherapy, and the diversity of intestinal flora decreased significantly in patients with diarrhoea after radiotherapy. Five studies observed that the community composition of the gut microbiota changed at the phylum, order or genus level before, during, and after pelvic radiotherapy at different time points. In addition, the composition of the gut microbiota before radiotherapy was different between patients with postradiotherapy diarrhoea and those without diarrhoea in five studies. However, relevant studies have not reached consistent results regarding the changes in microbiota composition. Changes in the intestinal flora induced by pelvic radiotherapy and their relationship between changes in intestinal flora and the occurrence of radiation-induced diarrhoea (RID) are discussed in this study, providing a theoretical basis for the causes of RID after pelvic radiotherapy.

The effect of chronoradiotherapy on cervical cancer patients: A multicenter randomized controlled study

“…Diarrhea caused by radiotherapy in the pelvic region is mainly caused by intestinal crypt cell apoptosis ( 25 ). In a study of the intestinal crypt in mice, an obvious circadian rhythm was observed in the number of apoptotic cells in the intestinal crypt during the administration of radiotherapy at different times, which indicated that radiotherapy-induced apoptosis occurs in a time-dependent manner ( 26 , 27 ).…”

Exploiting dietary fibre and the gut microbiota in pelvic radiotherapy patients

“…Specific changes in bacterial composition were also reported, although the findings remain inconsistent. Overall, the consensus observation is an increase in phyla Proteobacteria, Fusobacteria and unclassified bacteria and a decrease in phyla Firmicutes and Bacteroidetes and genera Faecalibacterium and Bifidobacterium following pelvic radiotherapy [61,62]. Characteristic pre-radiotherapy microbial compositions were seen in patients who later developed RE during pelvic irradiation [59] or post-radiation diarrhoea [17] and in patients demonstrating improved survival [8].…”

“…Specific changes in bacterial composition were also reported, although the findings remain inconsistent. Overall, the consensus observation is an increase in phyla Proteobacteria, Fusobacteria and unclassified bacteria and a decrease in phyla Firmicutes and Bacteroidetes and genera Faecalibacterium and Bifidobacterium following pelvic radiotherapy [ 61 , 62 ].…”

New Insights into the Relationship between Gut Microbiota and Radiotherapy for Cancer

“…In addition to RE, diarrhea is also a common radiation-related intestinal injury. Some studies have observed that pelvic radiotherapy can cause changes in the community composition of the gut microbiota at the level of phyla, order, or genus [ 85 ]. Among them, the potential protective effects of Bifidobacterium , Clostridium cluster XIVa , and Faecalibacterium prausnitzii are reduced, and Enterobacteriaceae and Bacteroidetes are increased, which may especially lead to diarrhea [ 86 ].…”