Phase 3 RCT (NRG-GU005) comparing SBRT (36.25 Gy in 5 fractions, n=353) vs moderately hypofractionated IMRT (70 Gy in 28 fractions or 60 Gy in 20 fractions, n=345) in 698 patients with localized intermediate-risk prostate cancer (clinical stage T1-T2b), with co-primary endpoints of patient-reported quality-of-life (EPIC-26 urinary irritative/obstructive and bowel domains) at 2 years and disease-free survival (DFS) at 3 years.
SBRT did not improve urinary irritative/obstructive quality of life vs MH-IMRT (MCID: 35.4% vs 33.7%, P=.68), but significantly reduced bowel MCID (34.9% vs 43.8%, P=.03) and grade 3-4 GU adverse events (0.6% vs 2.5%, P=.04); DFS at 3 years favored MH-IMRT (92.1% vs 88.6%), with SBRT failing to demonstrate superiority.
Median follow-up of only 3.2 years is short for a disease with long natural history; the SBRT dose prescription (36.25 Gy) was modest and may not represent optimal SBRT dosing; open-label design introduces potential reporting bias in patient-reported outcomes.
SBRT (5 fractions) offers fewer bowel quality-of-life declines and fewer severe GU toxicities than MH-IMRT for intermediate-risk prostate cancer, but did not match MH-IMRT's 3-year DFS; clinicians should weigh convenience and toxicity profile against the observed DFS difference, which may narrow with longer follow-up.
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