Impact of a Reminder App on Bladder Filling During Moderately Hypo-Fractionated Radiotherapy for Prostate Cancer: Results of the REFILL-PAC-HYPO Trial

Background/Objectives: Moderate hypo-fractionation is frequently used for irradiation of prostate cancer. Irrespective of dose fractionation, radiotherapy can lead to radiation cystitis. To reduce urinary toxicity, it is important to avoid bladder volumes < 200 mL. This may be facilitated with an app reminding patients to drink water prior to irradiation. This non-randomized multicenter REFILL-PAC-HYPO trial with external control evaluated the association between use of the reminder app and bladder filling during a radiotherapy course. Methods: Twenty-two patients receiving hypo-fractionated irradiation (20 × 3.0 Gy) were planned to be supported by the app (the prospective experimental group) and compared to 95 patients who were not supported by the app (the historical control group). The primary endpoint was the number of fractions with a bladder volume < 200 mL. Secondary objectives included satisfaction with the app and its impact on using health technology. Results: The median number of fractions with a bladder volume < 200 mL was lower in the app-supported experimental group (13; interquartile range: 6, 18 vs. 19; interquartile range: 14, 20). The Wilcoxon–Mann–Whitney test indicated a significant between-group difference (p = 0.0009) with a Hodges–Lehmann estimate of −4 fractions (95% confidence interval: −7 to −2). Supportive analyses used a multivariable negative binomial model (rate ratio: 0.71; p = 0.0018) and propensity score analysis (p = 0.012). The dissatisfaction rate was 20%; 78.9% of patients stated at least a little impact of trial participation on the use of health technology. Conclusions: Given the limitations of this study, the app was associated with fewer fractions with a bladder volume < 200 mL in this cohort. Although patient dissatisfaction was considered acceptable, further optimization of the app would be welcomed. Moreover, the findings of this study require confirmation in a randomized trial that also considers urinary toxicity.