EMPTY-RT: A Phase 2 Trial of Prostate Stereotactic Body Radiotherapy with an Empty Bladder Approach

Area of Science:

• Radiation Oncology
• Urologic Oncology

Background:

• Prostate stereotactic body radiation therapy (SBRT) is an effective treatment for prostate cancer.
• Standard protocols often utilize a full bladder to create a consistent treatment volume.
• Variability in bladder filling can impact treatment precision and safety.

Purpose of the Study:

• To assess the feasibility and dosimetric safety of performing prostate SBRT with an empty bladder approach.
• To evaluate the rate of acute urinary toxicity compared to established benchmarks.

Main Methods:

• 139 patients with prostate cancer underwent SBRT planning with an empty bladder.
• Participants voided before planning CT scans and SBRT fractions.
• Interfraction bladder volume variability was assessed using cone-beam CT.
• The primary endpoint was the rate of acute grade 2+ urinary adverse events (AEs).

Main Results:

• 118 patients were evaluable for safety in the empty bladder cohort.
• The median empty bladder volume was 77 cc, with 18% interfraction variation.
• The rate of grade ≥2 urinary AEs was 28.1%, meeting the non-inferiority threshold.
• Higher initial bladder volume correlated with increased risk of urinary AEs (OR 1.02).
• Once-weekly SBRT was associated with fewer gastrointestinal AEs.

Conclusions:

• Prostate SBRT with an empty bladder is dosimetrically feasible and reproducible.
• Acute safety is comparable to standard full bladder protocols.
• This approach may provide a time-efficient and patient-friendly alternative for routine prostate SBRT.