Impact of bowel preparation compliance on interfractional rectal diameter variation during prostate cancer radiotherapy

Abstract

Radiation therapy, a mainstay of management for prostate cancer, may lead to variations in rectal volume and subsequent toxicities. This study examines the role of bowel preparation compliance and Milk of Magnesia (MoM), on rectal diameter, toxicities, and volume variations during image-guided radiotherapy (IGRT). Through this, we aim to enhance treatment precision and reduce rectal toxicity, improving patient outcomes in pelvic irradiation. This prospective observational study, conducted at the Aga Khan University between July 2024 and December 2024, included prostate cancer patients receiving pelvic radiotherapy. Patients underwent a standardized bowel preparation protocol involving an antiflatulence diet and Milk of Magnesia (MoM) in an attempt to reduce rectal volume and toxicity, with bladder preparation requiring 500 mL of water intake 30 minutes before scans. Daily cone beam CT (CBCT) images ensured accurate target coverage, and rectal parameters were monitored throughout treatment. Data on patient compliance, rectal volume, interfractional motion, and toxicity were collected using the Adaptive Radiotherapy Integrated Algorithm (ARIA) system and self-designed questionnaires, with statistical analyses, including mixed-model logistic regression, assessing the relationship between various factors and treatment-related toxicity, defined as significant at p < 0.05. A total of 145 scans involving 7 prostate cancer patients undergoing radiotherapy were analyzed, with a mean patient age of 63.9 years and mean diagnostic serum PSA levels of 27.0 ng/ml. Most patients had a Gleason score of 5 and were treated primarily with Volumetric Modulated Arc Therapy (VMAT), receiving a radiation dose of 7800 cGy over 39 fractions. Compliance with bowel preparation protocols and Milk of Magnesia (MoM) was suboptimal (25.5%). Statistical analysis revealed a significant association between MoM compliance and reduced rectal toxicity, while dietary compliance, although beneficial, did not achieve significance in multivariable models. The mean rectal dose during treatment increased significantly, while individual variations in rectal diameter and volume were observed. This study emphasizes the importance of strict adherence to bowel preparation protocols and MoM in mitigating rectal toxicity and improving patient outcomes in pelvic irradiation for prostate cancer.

Keywords: Acute toxicity; Bowel preparation; Milk of magnesia; Patient compliance; Prostatic neoplasms; Radiotherapy.