Prostate
Low/intermediate-risk fractionation: the first of the modern SBRT-vs-hypofx trials to stratify by rectal spacer, so the toxicity signal is not spacer-confounded.
NRG-GU005 NCT03367702
ForLocalized favorable intermediate-risk prostate, T1-T2b, GG1-2, PSA <20
88.6% vs 92.1%
SBRT not superior; adjusted HR 1.40 (0.91-2.13), P=.12
TL;DR3yr DFS 88.6% SBRT vs 92.1% MH-IMRT, superiority rejected (adjusted HR 1.40, 0.91-2.13); bowel and GU toxicity favored SBRT.
The number that should move practice is biochemical failure: 7.8% vs 4.2% at 3yr (adj HR 1.82, 1.01-3.27), while local failure was flat at 1.2% vs 1.0%. The SBRT prescription was deliberately modest, 36.25 Gy/5 fx with dose uniformity prioritized and urethral max held to 38.78 Gy, so this reads as a dose and margin question, not a verdict on 5 fractions.
In favorable intermediate-risk localized prostate cancer choosing between 5-fraction SBRT and moderate hypofractionation, this supports the toxicity and convenience case for SBRT while flagging a 3-year PSA-failure gap; it does not speak to unfavorable intermediate or high-risk disease, or to dose-escalated SBRT regimens.
Biochemical failure, not DFS, carries the read: 7.8% vs 4.2% at 3yr (adj HR 1.82, 1.01-3.27) with local failure flat at 1.2% vs 1.0%. The prescription was deliberately uniform, 36.25 Gy/5 fx with urethral max 38.78 Gy and no focal boost, so this argues about dose and margin rather than about 5 fractions.
Also covered Jul 8
13 details 5 trials watching
Phase 3, international, open-label, 1:1 randomized superiority trial across 136 centers, accruing November 2017 to June 2022 with last follow-up October 2024. N=698 randomized (353 SBRT, 345 MH-IMRT), median follow-up 3.2 years. Two coprimary end points, patient-reported QoL and DFS, each tested at 2-sided alpha .05 with no study-wise correction, so both had to be positive for a positive trial.
Localized cT1-T2b, either Gleason 3+4 (GG2) with PSA <20 ng/mL or Gleason 3+3 (GG1) with PSA 10-20 ng/mL. Median age 68 (range 42-84); 80% White, 13% Black, 3% Asian; 81.7% T1c and 88.1% Zubrod 0. Stratified by risk group and by rectal manipulation, of whom 55.6% used spacer alone and 40.3% no device.
SBRT 36.25 Gy in 5 fractions (7.25 Gy per fraction), delivered as prescribed in 96.6%; MH-IMRT 70 Gy/28 fx in 70.6% or 60 Gy/20 fx in 26.6%. Rectal constraints were max 38 Gy to 0.03 mL and 18 Gy to 50%; bladder 39 Gy and 15 Gy. Where PTV max exceeded 38.78 Gy the urethra had to be contoured and capped at 38.78 Gy, a deliberately uniform, non-escalated prescription. Protocol-compliant or acceptable variation in 97.7% and 97.2% of arms.
Coprimary: MCID frequency in EPIC-26 urinary irritative/obstructive and bowel domains at 24 months, and DFS at 3 years (powered for HR 0.62). Secondary: the other EPIC-26 domains at 12 and 24 months, overall survival, biochemical DFS, regional and distant failure. EPIC-26 adherence was 82% at 1yr and 84% at 2yr.
Urinary irritative/obstructive MCID was flat (35.4% vs 33.7%, P=.68); bowel MCID favored SBRT (34.9% vs 43.8%, P=.03). DFS superiority was rejected at a 91-event interim (HR 1.38, 0.91-2.09), with 3yr rates 88.6% vs 92.1% and no adjusted difference (HR 1.40, P=.12).
| Endpoint | SBRT | MH-IMRT | Effect |
|---|---|---|---|
| Biochemical failure | 7.8% | 4.2% | adj HR 1.82 (1.01-3.27), P=.046 |
| Local failure | 1.2% | 1.0% | P=.97 |
| Overall survival | n/a | n/a | P=.65; adj HR 1.15 (0.55-2.41), P=.70 |
Grade 3+4 GU adverse events were lower with SBRT (0.6% vs 2.5%, P=.04), as were any-grade rectal hemorrhage (10.5% vs 17.3%, P=.01) and fatigue (39.2% vs 50.8%, P=.002). Longitudinal bowel scores favored SBRT (LS mean 2.68 [1.02-4.34], P=.002) and urinary incontinence scores likewise (LS mean 2.91 [0.85-4.97], P=.006).
PACE-B and HYPO-RT-PC established that 5-fraction prostate SBRT is tolerable and non-inferior on biochemical control; this trial asked the harder superiority question and lost it, and adds a rectal-manipulation stratification neither predecessor used, which balanced spacer use across arms rather than leaving it a center-level confounder.
The biochemical failure signal, the one result that argues against SBRT, sits on 3-year rates with a CI whose lower bound touches unity (adj HR 1.82, 1.01-3.27) and cannot be separated from the higher benign PSA bounce rate after SBRT, which the trial was not designed to distinguish from true failure. Local, regional and distant failure events were too few to analyze (8 vs 7, 4 vs 2, 4 vs 4), so the mechanism behind the PSA gap is unobserved.
The authors attribute the PSA-control gap to a possible lower biologically effective dose and smaller SBRT margins, the same two choices that plausibly produced the bowel benefit. If that trade is real, it is tunable: focal boost to the dominant intraprostatic lesion was explicitly excluded here and is where the next version of this question belongs.
CONSORT flow
Randomised phase 3, prespecified coprimary endpoints, ITT: the DFS superiority hypothesis was rejected and biochemical failure ran higher with SBRT, contesting the assumption 5 fractions cost nothing.
- Whether benign PSA bounce explains the biochemical failure gap
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