Timing Variability of Bladder Volumes in Men Receiving Radiotherapy to the Prostate

Background and Purpose: Dose-escalated external- beam radiotherapy improves outcomes for localized prostate cancer but risks increasing the toxicity. One strategy to decrease this toxicity may be larger and more consistent bladder volumes. The primary objective of this study was to determine the time required for 95% of patients on a dose-escalated external-beam radiotherapy protocol to comfortably achieve a 180-cc bladder volume. In addition, measurement of patients' subjective assessment of urgency related to bladder filling was obtained to determine the feasibility of bladder-filling instructions. Methodology: Thirty consenting patients with localized prostate cancer treated with external-beam radiotherapy were assigned 1: 1 to 250-cc vs. 500-cc water preload. After voiding, patients drank the specified fluid preload and had their bladder volume and urinary urgency assessed at regular intervals over 2 hours, repeated at weeks 1, 4, and 7. Results: The time required for 95% of patients to achieve a bladder volume of 180 cc was 75 and 57 minutes for groups 1 and 2, respectively (P = .03). Serum creatinine and use of bladder medications did not influence time to optimal bladder filling. Participants in group 2 reported moderate to severe urinary severity more frequently than participants in group 1. Conclusions: Time to optimal bladder volume was highly varied and was faster with a 500-cc fluid preload. Customizing the wait times based on calculated ultrasound-based filling rates appears feasible in a busy radiotherapy department.