Top Line: What is the risk of acute GI and GU effects from moderately hypofractionated radiation to the prostate fossa?
The Study: Early results from GU003 showed similar outcomes and late adverse effects with moderately hypofractionated prostate fossa radiation when compared to conventional fractionation. There’s definitely interest in shortening the 7-8 week course of treatment, however some studies with longer followup have raised concerns over a potential risk of seeing even later AEs beyond 2 years. Here’s a single arm phase 2 trial that enrolled 55 patients who were planned to receive post-prostatectomy radiation (mostly salvage, 89%). They received 54 Gy in 18 fractions to the prostate fossa with optional nodal coverage (5.5%). At an alpha/beta of 3, the EQD2 was estimated to be 65 Gy. Rectum objectives included V50 <5% and V40 <25%, and bladder objectives included V50 <8% and V40 <30%. Over half of patients received ADT (52.7%). The rate of acute grade 2 GU events was 5.5%, and the rate of grade 2 GI events was 34.5%. The rate of acute grade 2 events approached but didn’t exceed the primary endpoint of <37%. There was one acute small bowel obstruction. The rates of late grade 2 GU and GI events were 14.6% and 21.8%. The rate of late grade 3 GU events was 3.6% with no GI events.
TBL: In the context of other data, regimens like this show promise, but they need randomized comparison to conventional fractionation and long term followup. | Sawayanagi, Radiother Oncol 2026
The Study: Early results from GU003 showed similar outcomes and late adverse effects with moderately hypofractionated prostate fossa radiation when compared to conventional fractionation. There’s definitely interest in shortening the 7-8 week course of treatment, however some studies with longer followup have raised concerns over a potential risk of seeing even later AEs beyond 2 years. Here’s a single arm phase 2 trial that enrolled 55 patients who were planned to receive post-prostatectomy radiation (mostly salvage, 89%). They received 54 Gy in 18 fractions to the prostate fossa with optional nodal coverage (5.5%). At an alpha/beta of 3, the EQD2 was estimated to be 65 Gy. Rectum objectives included V50 <5% and V40 <25%, and bladder objectives included V50 <8% and V40 <30%. Over half of patients received ADT (52.7%). The rate of acute grade 2 GU events was 5.5%, and the rate of grade 2 GI events was 34.5%. The rate of acute grade 2 events approached but didn’t exceed the primary endpoint of <37%. There was one acute small bowel obstruction. The rates of late grade 2 GU and GI events were 14.6% and 21.8%. The rate of late grade 3 GU events was 3.6% with no GI events.
TBL: In the context of other data, regimens like this show promise, but they need randomized comparison to conventional fractionation and long term followup. | Sawayanagi, Radiother Oncol 2026