The Effects of Probiotic–Prebiotic Use on Acute Inflammatory Parameters in Patients Receiving Pelvic Radiotherapy: A Prospective Multicenter Study

<b>Background:</b> This is the first prospective clinical study to evaluate the impact of prebiotic and probiotic use on acute radiation-induced pelvic side effects and associated changes in serum cytokine levels in patients with pelvic malignancies. <b>Methods:</b> This multicenter prospective study included 80 patients with pelvic cancers treated at two centers between 2021 and 2023. Patients were divided into three groups: probiotic + prebiotic, prebiotic only, and nonsupplemented. Serum cytokine levels (tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6) and radiation-related side effect scores were assessed at the beginning of pelvic radiotherapy (RT) and again at the fifth week. Based on data normality, the Wilcoxon signed-rank test was used for statistical analysis. <b>Results:</b> According to side effect scores, in the prebiotic-only group, a modest yet statistically significant increase in fecal incontinence (FI; <i>p</i>=0.040) and blood and mucus in the stool (BMS; <i>p</i>=0.049) was observed. Conversely, the probiotic + prebiotic group showed a significant increase in dysuria (<i>p</i>=0.001) and impotence (<i>p</i>=0.016). IL-6 levels significantly increased in the prebiotic-only group (<i>p</i>=0.035), while TNF-α levels rose significantly in the group without any nutritional support (<i>p</i>=0.025). No significant increase in cytokine levels or intestinal side effects was observed in the combined probiotic + prebiotic group (<i>p</i> > 0.05 for all comparisons). <b>Conclusions:</b> The absence of a rise in cytokine levels and intestinal toxicity in the probiotic + prebiotic group suggests that probiotics may play a role in mitigating radiation-induced intestinal side effects and inflammatory responses.