*2.3. Gut Microbiota and Radiotherapy*

Radiotherapy results in dysregulation of the gut microbiota, which negatively affects the diversity and richness of gut bacterial diversity, potentially causing an enrichment of harmful microbiota (*Proteobacteria* and *Fusobacteria*) and a decrease in beneficial microbiota (*Faecalibacterium* and *Bifidobacterium*) [47,48]. El Alam et al. discovered a significant alteration in the gut microbiome composition during pelvic chemotherapy and radiotherapy (CRT), with increases in *Proteobacteria* and decreases in *Clostridiales*, whereas after CRT, the gut microbiome composition changed, with increases in *Bacteroides* species [49]. Intestinal radiation injury is a disorder that can be influenced by radiotherapy, by altering bacteria that produce short-chain fatty acids (SCFAs) [48]. Uncertainty persists regarding the effect of SCFAs on the prevalence of various disorders.
