Top Line: Does an empty bladder increase urinary effects from prostate SBRT?
The Study: Most people treat prostate cancer patients with a full bladder. The idea is that increased bladder volume moves much of the bladder up and out of the irradiated volume. This improves bladder volumetric dosimetry while also helping to reduce bowel dose. The problem is that the links in the causal chain between bladder volume, dosimetry, and adverse effects are fairly weak. Bladder volume is highly variable and the actual dose received by the bladder may not correlate well with the planned dose. Furthermore, baseline patient factors have a bigger impact on GU effects. EMPTY-RT was a phase 2 trial that evaluated the safety and feasibility of empty bladder prostate SBRT. It included 132 patients planned to receive SBRT. All were planned with empty bladder, and 85% had optimal or acceptable bladder dosimetry. Those who didn’t were treated with full bladder. They received 35-36.25 Gy in 5 fractions to the prostate with 39% also receiving 25 Gy in 5 fraction to the pelvic nodes. The median empty bladder volume was 77 cc, and interfraction volume variation was 18%. The cumulative incidence of acute grade 2+ GU events was 28.1%, which fell below the primary endpoint threshold of 32% based on prior SBRT trials. There was only 1 (0.9%) grade 3 GU event. On multivariable analysis, larger empty bladder volume (likely suggesting baseline urinary dysfunction) was associated with a higher risk of grade 2+ effects. This doesn’t necessarily mean it’s time to drop the full bladder convention, but it does show the inconsistent relationship between bladder filling and adverse effects and the more important influence of baseline patient urinary function.
TBL: In this single arm phase 2 study, empty bladder prostate SBRT was dosimetrically feasible in most patients and had an acceptable rate of acute GU effects. | Murthy, Int J Radiat Oncol Biol Phys 2026
The Study: Most people treat prostate cancer patients with a full bladder. The idea is that increased bladder volume moves much of the bladder up and out of the irradiated volume. This improves bladder volumetric dosimetry while also helping to reduce bowel dose. The problem is that the links in the causal chain between bladder volume, dosimetry, and adverse effects are fairly weak. Bladder volume is highly variable and the actual dose received by the bladder may not correlate well with the planned dose. Furthermore, baseline patient factors have a bigger impact on GU effects. EMPTY-RT was a phase 2 trial that evaluated the safety and feasibility of empty bladder prostate SBRT. It included 132 patients planned to receive SBRT. All were planned with empty bladder, and 85% had optimal or acceptable bladder dosimetry. Those who didn’t were treated with full bladder. They received 35-36.25 Gy in 5 fractions to the prostate with 39% also receiving 25 Gy in 5 fraction to the pelvic nodes. The median empty bladder volume was 77 cc, and interfraction volume variation was 18%. The cumulative incidence of acute grade 2+ GU events was 28.1%, which fell below the primary endpoint threshold of 32% based on prior SBRT trials. There was only 1 (0.9%) grade 3 GU event. On multivariable analysis, larger empty bladder volume (likely suggesting baseline urinary dysfunction) was associated with a higher risk of grade 2+ effects. This doesn’t necessarily mean it’s time to drop the full bladder convention, but it does show the inconsistent relationship between bladder filling and adverse effects and the more important influence of baseline patient urinary function.
TBL: In this single arm phase 2 study, empty bladder prostate SBRT was dosimetrically feasible in most patients and had an acceptable rate of acute GU effects. | Murthy, Int J Radiat Oncol Biol Phys 2026