# A Reminder App to Optimize Bladder Filling During Radiotherapy for Patients With Prostate Cancer (REFILL-PAC): Protocol for a Prospective Trial

## TL;DR

This study tests a mobile app to help prostate cancer patients drink more water before radiotherapy to reduce bladder-related side effects.

## Contribution

This is the first trial to evaluate a reminder app's impact on bladder filling during prostate cancer radiotherapy.

## Key findings

- The app aims to increase bladder volumes above 200 ml during radiotherapy fractions.
- The study will assess adherence and bladder filling outcomes in patients using the app.
- Results may inform new strategies to reduce urinary toxicity in prostate cancer radiotherapy.

## Abstract

Many patients with nonmetastatic prostate cancer receive radiotherapy, which may be associated with acute cystitis, particularly if the volume of the urinary bladder is small. Three studies showed bladder volumes <200 ml or <180 ml to be associated with increased urinary toxicity. Therefore, it is important to maintain bladder volumes greater than 200 ml during as many radiation fractions as possible. Several studies investigated drinking protocols, where patients were asked to drink a certain amount of water prior to radiotherapy sessions. This may require considerable discipline from the patients, who are predominantly older adults. Adherence to a drinking protocol may be facilitated by a mobile app that reminds patients to drink water prior to each radiation session. This study investigates the effect of such an app on bladder filling status in patients with prostate cancer undergoing external beam radiotherapy (EBRT) alone.

The primary goal of this study is to evaluate the impact of an app that reminds patients irradiated for prostate cancer to drink 300 ml of water prior to each radiotherapy session on the number of fractions with bladder volumes <200 ml during the radiotherapy course.

This ongoing phase 2 aims to recruit 28 patients treated with EBRT alone for nonmetastatic prostate cancer. Radiotherapy will be administered using normo-fractionation, with doses ranging from 70 to 80 Gy in 35 to 40 fractions of 2 Gy, preferably with volumetric-modulated arc therapy (VMAT). Treatment volumes include the prostate with or without the seminal vesicles.

Recruitment for this trial will start in March 2025 and is planned to be completed in October 2026. The study is scheduled to conclude in December 2026.

This trial is the first to evaluate the impact of a reminder app on the number of radiotherapy fractions with bladder volumes <200 ml in patients undergoing irradiation for localized prostate cancer.

Clinicaltrials.gov NCT06653751; https://clinicaltrials.gov/show/NCT06653751

PRR1-10.2196/68179