SBRT Reduces Bowel Toxicity in Localized Intermediate-Risk Prostate Cancer

A phase 3 international trial has demonstrated that stereotactic body radiotherapy (SBRT) significantly reduced long-term bowel complications compared to moderately hypofractionated intensity-modulated radiation therapy (MH-IMRT) in localized intermediate-risk prostate cancer. Findings from the NRG Oncology trial NRG-GU005 (NCT03367702) were published in JAMA.

Although the trial did not meet co-primary endpoints of SBRT superiority in disease-free survival (DFS) and overall quality of life, it provided insights into how fractionation schedules impact patient-reported outcomes. For oncology nurses, these results can offer a guide to counseling patients on the distinct risks and physical impacts of shortened radiation courses.

Study Design and Technology Comparison

Standard moderately hypofractionated regimens require 20 to 28 daily treatments over 4 to 6 weeks. SBRT is an ultra-hypofractionated approach delivering a concentrated radiation dose in five sessions over 1 to 2 weeks. The NRG-GU005 trial randomized 698 patients across 136 centers to SBRT (36.25 Gy in 5 fractions; n = 353) or MH-IMRT (70 Gy in 28 fractions or 60 Gy in 20 fractions; n = 345). Co-primary endpoints were DFS at 3 years and the frequency of a minimal clinically important decline (MCID) in bowel and urinary irritative/obstructive domains at two years.

Key Quality-of-Life Takeaways for Oncology Nurses

The patient-reported findings showcase SBRT's superior tolerability in multiple functional domains. Key quality-of-life takeaways include:

• Bowel Preservation: SBRT significantly reduced clinically meaningful bowel decline. At 2 years, 34.9% of SBRT patients experienced an MCID in the EPIC bowel domain, compared to 43.8% of IMRT patients (p = 0.03). This bowel preservation was also evident at 1 year (33.1% vs. 45.9%, p = 0.002).
• Less Urinary Incontinence: Patients in the SBRT cohort experienced significantly less urinary incontinence at both 1 year and 2 years (25.9% vs. 34.7% at 2 years, p = 0.02).
• Lower Adverse Rates: SBRT patients reported significantly less rectal hemorrhage of any grade (10.5% vs. 17.3%, p = 0.01) and overall fatigue (39.2% vs. 50.8%, p = 0.002).
• Fewer Severe Genitourinary Events: Grade 3 or 4 genitourinary adverse events were significantly lower in the SBRT group (0.6%) compared to the MH-IMRT group (2.5%, p = 0.04).
• Preserved Sexual Function: SBRT patients reported fewer clinically meaningful declines in sexual function at 1 year (34.3% vs. 43.9%, p = 0.03).
• Benefit of Rectal Spacers: Longitudinal analysis showed that rectal spacing devices were significantly associated with improved bowel function across both cohorts (p = 0.001), while omitting rectal manipulation led to worse bowel scores.

Efficacy Outcomes and Clinical Nuances

Despite quality-of-life advantages, SBRT was not superior to MH-IMRT in cancer control. The 3-year DFS was 92.1% for MH-IMRT compared to 88.6% for SBRT, crossing the pre-specified futility boundary. Furthermore, the rate of biochemical recurrence—determined by PSA failure—was significantly higher in the SBRT group (7.8% vs. 4.2%, p = 0.04). This difference may stem from the lower biologically effective dose used in this SBRT protocol (36.25 Gy) compared to other SBRT trials like PACE-B, which permitted a 15% higher dose. The lower dose in NRG-GU005 prioritized quality-of-life outcomes but yielded inferior biochemical control.

Actionable Nursing Implications

As frontline educators, oncology nurses must synthesize these complex trade-offs during patient consultations. Actionable nursing practice implications include:

• Shared Decision-Making: Counsel patients that SBRT offers convenience (5 treatments vs. 20-28) and lower impact on long-term bowel, bladder, and sexual function, but carries a higher risk of early biochemical PSA failure.
• Educate on Rectal Spacers: Advise eligible patients on the therapeutic benefits of using a rectal spacer during treatment to protect rectal tissue and preserve bowel quality of life.
• Manage Side-Effect Expectations: Reassure patients that while mild-to-moderate fatigue and bowel irritation can occur, SBRT is associated with less severe fatigue and lower rates of rectal bleeding than daily radiation.
• Monitor PSA Kinetics: Keep patients informed about the possibility of benign PSA bounces after SBRT, helping to alleviate anxiety during routine post-treatment surveillance.

References

1. NRG Oncology Trial Results Show Favorable Bowel Health Related Quality of Life Outcomes for Localized Immediate Risk Prostate Cancer Treated with Stereotactic Body Radiation Therapy – Results Published. Press Release. Philadelphia, PA: NRG Oncology; August 25, 2026.
2. Ellis RJ, Pugh SL, Yu JB, et al. Stereotactic Body Radiotherapy vs Moderately Hypofractionated IMRT for Localized Intermediate-Risk Prostate Cancer: A Randomized Clinical Trial. JAMA. Published online August 13, 2026. doi:10.1001/jama.2026.12627