# Gut Microbiota Is Not Significantly Altered by Radioiodine Therapy

## TL;DR

This study found that radioiodine therapy does not significantly change the gut microbiota, unlike traditional radiotherapy.

## Contribution

The study is the first to investigate the effect of radioiodine therapy on gut microbiota, highlighting its distinct impact compared to radiotherapy.

## Key findings

- Gut microbiome richness and diversity remained unchanged after radioiodine therapy.
- Only minor compositional changes were observed, especially in patients with hyperthyroidism.
- Radioiodine therapy does not cause major disruptions to the human gut microbiota.

## Abstract

Purpose: Radiotherapy treatments are known to alter the gut microbiota. However, little is known regarding the effect of nuclear medicine treatments on gut microbiota, and it is established that nuclear medicine is inherently different from radiotherapy. To address this knowledge gap, we conducted a prospective study to identify changes in the gut microbiota of patients treated with [131I]NaI by comparing fecal samples before and after RAIT. Methods: Fecal samples of 64 patients (37 with thyroid cancer and 27 with hyperthyroidism) with indication for RAIT were collected 2 to 3 days before treatment and 8 to 10 days post-treatment. After DNA extraction, the gut microbiota’s richness, diversity, and composition were analyzed by shotgun metagenomics. In addition, LEfSe was performed to compare compositional changes in specific bacteria. Results: Gut microbiome richness and diversity remained unchanged after RAIT, with few changes in its composition identified, especially in patients with hyperthyroidism. Conclusions: This study provides a conceptual and analytical basis for increasing our understanding of the effects of radiopharmaceuticals on gut microbiota. Our preliminary results indicate that RAIT, contrary to radiotherapy, does not cause major disruptions to the human gut microbiota.