Pre‑Treatment Ultrasound for Bladder Volume Verification In Prostate Radiotherapy: Effects on Workflow and Dosimetric Endpoints
Abstract
Purpose
Consistent bladder filling is a critical determinant of dosimetric accuracy and organ-at-risk (OAR) sparing in prostate radiotherapy (RT). This retrospective study evaluates whether the implementation of a dedicated ultrasound (US) scanner to assess bladder volume prior to table setup improves clinical workflow efficiency and dosimetric endpoints compared to standard verification protocols.
Methods
Sixty patients treated with Volumetric Modulated Arc Therapy (VMAT) were retrospectively analyzed across three distinct cohorts (n=20 each): Prostate only (P) (70.2Gy/26 Fx), Prostate with Lymph Nodes (P+LN) (80Gy/40 Fx+6Gy boost), and Prostate Bed with Lymph Nodes (PB+LN) (68Gy PTV/52.7 Gy LN/34 Fx). Within each group, 10 patients received pre-treatment US evaluation using the BladderScan Prime Plus (Verathon Inc.), while 10 served as the control group. The primary endpoint was the frequency of repeated Cone Beam CT (CBCT) scans due to unacceptable bladder filling. For ten patients in the P group (five control + five US), bladder volumes were measured across all fractions via CBCT. Dosimetric impact was assessed by overlaying treatment plans on CBCT images to recalculate doses to the bladder and PTV for the first three fractions of every patient
Results
Clinical workflow significantly improved in the US cohort, which required zero repeat CBCTs. Conversely, the control group required frequent rescans: P (2.0±1.87), P+LN (5.5±4.42), and PB+LN (2.5±2.32). Bladder volume deviations from simulation were significantly lower in the US group compared to controls (8.5±12.3% vs. -12.4±25.1%, P < 0.001). While the US group showed a lower mean D35% to the bladder (10.1±6.8Gy vs. 12.5±6.1Gy), this did not reach statistical significance (P = 0.24).
Conclusion
Pre-treatment US bladder volume evaluation effectively eliminates the need for repeat CBCTs, thereby reducing patient imaging dose and on-table time. This modality ensures a more consistent setup, optimizing Linac utilization and streamlining the overall clinical workflow for prostate cancer patients.