Role of non-absorbable oral antibiotics in bowel preparation for intracavitary brachytherapy: effects of rifaximin on rectal dosimetric parameters during vaginal cuff brachytherapy

PURPOSE: Brachytherapy is a major tool for dose escalation in gynecological cancer treatment. Control of rectal repletion is particularly challenging; it can impact dose received by this organ at risk and there are reported toxicities. The use of methods, such as enema and bowel preparation, to reduce rectal volume is a difficult process for patients, and its repeatability requires patients’ cooperation. Due to the effect of antibiotics on reducing intestinal gases, this study was conducted to measure the effect of adding rifaximin to bowel preparation on rectal dose-volume histogram (DVH) parameters. MATERIAL AND METHODS: In this prospective interventional study, 24 patients with cervical and endometrial cancer were treated with adjuvant high-dose-rate (HDR) brachytherapy. Both first and second sessions of brachytherapy were performed with bowel preparation, before and after the administration of rifaximin, respectively. The rectum was contoured as an organ at risk, and DVH parameters were recorded and compared in both sessions using magnetic resonance imaging (MRI)-based 3D treatment planning system. RESULTS: Rifaximin consumption reduced the rectal volume (p = 0.01), but had no significant correlation with other DVH parameters, especially D(2cc) (p = 0.599). Moreover, rectal volume had no significant correlation with DVH parameters (all p-values ≤ 0.05). CONCLUSIONS: Even though the addition of rifaximin to bowel preparation significantly reduced rectal volume, no significant difference was observed in DVH parameters. Therefore, it is recommended that adjuvant vaginal cuff HDR brachytherapy should be performed without the use of rifaximin, until further researches’ validate its effects.