Top Line: Is single fraction prostate SBRT safe and effective?
The Study: Five fraction SBRT is now a well established standard option for treating prostate cancer. But there’s still the allure of offering a single, definitive, noninvasive treatment for prostate cancer. ONE-SHOT was a single arm, phase 1/2 study that enrolled 45 patients with intermediate risk prostate cancer with no transition zone involvement and prostate volume < 70 cc. They were treated with single fraction SBRT with a prescription dose of 19 Gy in 1 fraction. The PTV was a 5 mm expansion of the prostate CTV (except 3 mm posterior). A urinary catheter was placed to delineate the urethra and a urethra PRV was used to limit the urethra maximum dose to 17 Gy. The primary endpoint of biochemical recurrence free survival was 92.9% at 3 years and 88% at 5 years. There were no acute grade 3 GU events, 42.5% had grade 1 GU events, and 20% had grade 2 GU events. At 3 years, the rates of grade 1 and 2 GU events were 43.9% and 9.8%, respectively. Only 12.2% had acute GI events, and at 3 years 7.3% experienced grade 1 events and 4.9% experienced grade 2 events. There was one case of late grade 3 rectal bleeding. This sounds encouraging, but the HDR experience raises caution where trials of single fraction HDR at similar dose resulted in unacceptable rates of local failure compared to multi-fraction HDR. Does SBRT work differently, or might more local failures emerge with longer follow up?
TBL: Early results from this trial of single fraction SBRT show encouraging results and relatively mild adverse effects, but longer follow up and larger trials are needed. | Zilli, JAMA Oncol 2026
The Study: Five fraction SBRT is now a well established standard option for treating prostate cancer. But there’s still the allure of offering a single, definitive, noninvasive treatment for prostate cancer. ONE-SHOT was a single arm, phase 1/2 study that enrolled 45 patients with intermediate risk prostate cancer with no transition zone involvement and prostate volume < 70 cc. They were treated with single fraction SBRT with a prescription dose of 19 Gy in 1 fraction. The PTV was a 5 mm expansion of the prostate CTV (except 3 mm posterior). A urinary catheter was placed to delineate the urethra and a urethra PRV was used to limit the urethra maximum dose to 17 Gy. The primary endpoint of biochemical recurrence free survival was 92.9% at 3 years and 88% at 5 years. There were no acute grade 3 GU events, 42.5% had grade 1 GU events, and 20% had grade 2 GU events. At 3 years, the rates of grade 1 and 2 GU events were 43.9% and 9.8%, respectively. Only 12.2% had acute GI events, and at 3 years 7.3% experienced grade 1 events and 4.9% experienced grade 2 events. There was one case of late grade 3 rectal bleeding. This sounds encouraging, but the HDR experience raises caution where trials of single fraction HDR at similar dose resulted in unacceptable rates of local failure compared to multi-fraction HDR. Does SBRT work differently, or might more local failures emerge with longer follow up?
TBL: Early results from this trial of single fraction SBRT show encouraging results and relatively mild adverse effects, but longer follow up and larger trials are needed. | Zilli, JAMA Oncol 2026