KEY POINTS
- EMPTY-RT was a prospective single-arm phase II study evaluating prostate SBRT immediately after voiding. Of 139 patients screened, 118 ultimately received all treatment using the empty-bladder workflow.
- Patients received 35–36.25 Gy in five fractions to the prostate, with 25 Gy in five fractions to pelvic nodes when indicated. Treatment was delivered on alternate days or once weekly using VMAT and daily CBCT soft-tissue matching.
- Empty-bladder planning was clinically acceptable in 118 of 139 patients (85%). Seven patients had simulation bladder volumes below 10 mL and 14 could not meet planning constraints and were switched to a full-bladder workflow.
- Median bladder volume at simulation was 77 mL, while median CBCT volumes during treatment were approximately 62–67 mL. Mean patient-level interfraction variation was 18%.
- Acute grade 2 or higher urinary toxicity occurred in 28.1% (90% CI 21.2–35.8%), below the prespecified non-inferiority limit of 42%. Only one patient (0.9%) experienced grade 3 urinary toxicity and required transurethral prostate resection.
- Grade 2 gastrointestinal toxicity occurred in 7.9%, with no grade 3 or higher gastrointestinal events. Once-weekly treatment was associated with fewer grade 2 gastrointestinal events than alternate-day SBRT, 0% versus 12.9% (p = 0.03), although treatment schedule was not randomized.
- Larger bladder volume at simulation independently predicted grade 2 or higher urinary toxicity (OR 1.02 per mL, 95% CI 1.01–1.03; p = 0.002), as did bladder V35Gy (OR 1.48, 95% CI 1.05–2.01; p = 0.03).
CLINICAL TAKEAWAY
Most patients undergoing prostate SBRT could be planned and treated safely without the inconvenience of maintaining a full bladder. The workflow is attractive for routine practice, but a randomized comparison is still needed to determine whether empty-bladder treatment is genuinely equivalent or superior in toxicity, dosimetry, and patient experience.
SOURCE
International Journal of Radiation Oncology, Biology, Physics