Feasibility Study Exploring the Effect of Pelvic Radiotherapy on the Intestinal Microbiome and Metabolome to Improve the Detection and Management of Gastrointestinal Toxicity.

Recruitment for the feasibility study was lower than anticipated, though attrition was low.

• 227 patients were screened, 69 were approached, and only 17 were recruited over 18 months.
• Mean age of recruited participants was 61.6 ± 15.3 years; 14 were female.
• There was 1 withdrawal, indicating low attrition among recruited participants.
• Participants underwent faecal sampling at three timepoints: baseline, week 4, and 6 months.

Baseline metabolome analysis showed lower heptanal and octanal in patients who later developed higher GI toxicity.

• Metabolome analysis was performed using gas chromatography-mass spectrometry (GC-MS).
• Patients were split into two groups based on IBDQ bowel subset (IBDQB) scores at week 4.
• Lower heptanal and octanal were detected in baseline faecal samples of patients with higher GI toxicity.
• The findings suggest these volatile compounds may serve as pre-treatment biomarkers for GI toxicity risk.

Week-4 metabolome analysis showed lower (methyltrisulfanyl)methane in patients with higher GI toxicity.

• This difference was identified in faecal samples collected at week 4 of radiotherapy.
• Metabolome grouping was based on IBDQB scores at week 4.
• GI toxicity was assessed using the Inflammatory Bowel Disease Questionnaire (IBDQ) bowel subset.

Month-6 metabolome analysis showed higher butanoic acid and benzaldehyde in patients with higher GI toxicity.

• Higher butanoic acid and benzaldehyde were found in 6-month faecal samples of patients with higher GI toxicity.
• Butanoic acid (butyrate) is a short-chain fatty acid with known roles in gut health and inflammation.
• These findings represent post-treatment metabolomic differences between GI toxicity groups.

Whole-group microbiome analysis showed a trend towards decreased alpha diversity at 4 weeks of radiotherapy.

• Microbiome analysis was performed using 16S rRNA sequencing.
• No significant differences in beta diversity were observed across the whole group.
• There was a trend towards increased Lachnoclostridium and decreased Ruminococcaceae Incertae sedis at week 4.
• These changes represent microbiome shifts occurring during the course of pelvic radiotherapy.

Patients with higher GI toxicity had lower alpha diversity at each timepoint compared to those with lower GI toxicity.

• Lower alpha diversity was observed in the high GI toxicity group at baseline, week 4, and 6 months.
• No significant difference in beta diversity was found between the GI toxicity groups.
• More genera were differentially abundant between GI toxicity groups at 4 weeks than at other timepoints.
• These findings suggest lower alpha diversity may predict GI toxicity from pelvic radiotherapy.

Approximately 80% of patients develop gastrointestinal symptoms during pelvic radiotherapy.

• The triggering event for GI symptoms is known, enabling identification of pathophysiological changes.
• GI toxicity was assessed using the IBDQ bowel (IBDQB) subset.
• The known timing of the triggering event (radiotherapy initiation) provides an opportunity to study sequential changes in the microbiome and metabolome.