Prostate cancer is particularly suited to precision radiation because the prostate is a relatively small organ that can be targeted from multiple directions while attempting to limit exposure to surrounding tissues. SBRT delivers a high biological dose in a small number of treatment sessions, using advanced image guidance and treatment planning to account for organ motion and anatomy. In NRG-GU005, patients assigned to the SBRT group received 36.25 Gy in five fractions. Patients in the comparison group received MH-IMRT, delivered either as 70 Gy in 28 fractions or 60 Gy in 20 fractions. While conventional radiation may require several weeks of daily visits, SBRT can be completed in approximately one week, a difference that could reduce travel, treatment costs, time away from work, and the logistical burden on patients and families.

The trial enrolled 698 evaluable participants with intermediate-risk disease and was designed around two co-primary endpoints: disease-free survival and patient-reported health-related quality of life. Researchers assessed quality of life with the 26-item Expanded Prostate Cancer Index Composite, commonly known as EPIC-26. The instrument measures treatment effects in several domains, including bowel function, urinary irritative and obstructive symptoms, urinary incontinence, sexual function, and hormonal symptoms. For the primary quality-of-life analysis, investigators focused on whether patients experienced a minimally clinically important difference, or MCID, in bowel health or urinary irritative and obstructive symptoms. An MCID is intended to represent a change noticeable and meaningful to patients rather than merely a statistically measurable difference in a score.

At two years, 34.9 percent of men treated with SBRT experienced an MCID in the bowel domain, compared with 43.8 percent of those treated with MH-IMRT. The difference was statistically significant, with a p value of 0.034, indicating that the probability of observing such a result by chance alone was relatively low under the study’s statistical assumptions. Longitudinal analyses, which examine changes over time rather than relying on a single follow-up point, also associated SBRT with improved bowel-domain scores. The use of rectal spacers was linked to better bowel outcomes as well. These devices are placed between the prostate and rectum to increase physical separation, potentially reducing the amount of radiation delivered to the rectal wall during treatment.

The bowel result did not extend to the trial’s urinary co-primary endpoint. An MCID in urinary irritative or obstructive symptoms occurred in 33.7 percent of patients in the SBRT arm and 34.7 percent in the MH-IMRT arm. The difference was not statistically significant, with a p value of 0.68. Urinary irritation and obstruction can result from radiation-related inflammation or changes in the prostate and urethra, and the similar rates in both groups suggest that delivering radiation in five fractions did not substantially alter this aspect of recovery compared with moderately shortened IMRT. Because both quality-of-life domains had to meet the prespecified criteria for the co-primary endpoint to be considered positive, the urinary result meant that the trial did not fulfill its overall health-related quality-of-life objective.

The study also did not establish a disease-control advantage for SBRT. An interim analysis crossed the trial’s futility boundary for superiority, meaning that the accumulating data made it unlikely that SBRT would ultimately prove superior to MH-IMRT for disease-free survival. According to the investigators, this conclusion was driven solely by a higher number of biochemical failures in the SBRT group. Biochemical failure is generally identified through rising prostate-specific antigen, or PSA, after treatment. PSA is a sensitive marker of prostate activity, but a biochemical recurrence does not always immediately correspond to visible metastatic disease or a decline in overall survival. Longer follow-up remains important because prostate cancer can recur many years after initial treatment, and early PSA patterns may not fully predict long-term clinical outcomes.

The investigators reported additional differences in patient-reported genitourinary outcomes. SBRT was associated with lower incontinence-related quality of life, indicating a less favorable experience in that specific domain, while it was also associated with improved maintenance of erectile dysfunction compared with MH-IMRT. These findings illustrate why radiation comparisons cannot be reduced to a single measure of toxicity. A treatment may perform better for bowel symptoms while producing different trade-offs in urinary continence or sexual function. The prostate, rectum, bladder, urethra, and neurovascular structures occupy a tightly packed region of the pelvis, and radiation dose, fraction size, baseline function, anatomy, technical planning, and the use of protective devices can all influence late effects.

The NRG-GU005 results add to evidence from other randomized studies examining shorter prostate radiation schedules. The PACE-B trial previously showed that SBRT was non-inferior to conventionally fractionated or moderately hypofractionated radiation for disease control in an appropriate patient population. NRG-GU005 was designed to ask a more demanding question: whether SBRT could deliver superior disease-free survival while also producing a clinically meaningful improvement in selected quality-of-life outcomes. The answer was no under the trial’s predefined criteria. Nevertheless, the bowel findings may be relevant to shared decision-making, particularly for patients who value fewer treatment visits and are concerned about gastrointestinal effects. Physicians will still need to weigh these potential advantages against urinary and sexual side effects, baseline symptoms, prostate anatomy, rectal spacer availability, and the uncertainty surrounding long-term biochemical control.

“This major clinical trial teaches us not only about state-of-the-art radiation technology, but also about the biology of radiation effects on prostate cancer and normal organs responsible for basic human functions,” Mitchell Machtay of Penn State, NRG Oncology’s group deputy chair and chief scientific officer, said in a statement. Rodney J. Ellis of the University of South Florida, the study’s lead author, said the trial was not positive overall but noted that SBRT produced a favorable outcome in the EPIC-26 bowel domain and not in the urinary irritative or obstructive domain. He emphasized that additional follow-up is needed to clarify longer-term outcomes. The trial was supported by the National Cancer Institute through the National Clinical Trials Network and conducted by NRG Oncology, a research group formed from the legacy Radiation Therapy Oncology Group, National Surgical Adjuvant Breast and Bowel Project, and Gynecologic Oncology Group programs. For now, the findings suggest that SBRT is a time-saving alternative with a distinct quality-of-life profile, not a universally superior replacement for MH-IMRT.

Subject of Research: SBRT versus moderately hypofractionated IMRT for localized intermediate-risk prostate cancer

Article Title: Stereotactic Body Radiotherapy vs Moderately Hypofractionated IMRT for Localized Intermediate-Risk Prostate Cancer: A Randomized Clinical Trial

News Publication Date: August 13, 2026

Web References: https://pubmed.ncbi.nlm.nih.gov/42593775/

References: 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.” Journal of the American Medical Association. 2026. doi:10.1001/jama.2026.12627.

Keywords: prostate cancer, SBRT, stereotactic body radiation therapy, IMRT, hypofractionated radiotherapy, NRG-GU005, radiation oncology, quality of life, EPIC-26, disease-free survival, PSA, rectal spacers

This multi-institutional trial enrolled 698 evaluable participants, randomly assigning them to either a regimen of SBRT at a dose of 36.25 Gy delivered in 5 fractions or to MH-IMRT administered either as 70 Gy in 28 fractions or 60 Gy in 20 fractions. The core objective was to evaluate patient-reported outcomes using the expanded Prostate Cancer Index Composite (EPIC-26) questionnaire, specifically focusing on the bowel and urinary irritation or obstruction domains at baseline, 12 months, and 24 months post-treatment. By assessing minimal clinically important decline (MCID), the study meticulously quantified nuanced changes in quality of life.

The EPIC-26 tool, a validated patient-reported outcome measure, enables quantification of symptoms impacting quality of life that are crucial for patients with prostate cancer, particularly in areas like bowel function and urinary control that often bear the brunt of radiation-induced toxicity. At the two-year mark post-treatment, the data demonstrated a statistically significant reduction in bowel-related MCID in patients treated with SBRT compared to those receiving MH-IMRT—34.9% versus 43.8% respectively, with a p-value of 0.034. This evidence implies a tangible benefit of SBRT in mitigating late bowel toxicity, a common and distressing side effect that compromises patients’ well-being.

Importantly, the trial also explored urinary health outcomes, analyzing the frequency of minimal clinically important declines related to urinary irritative or obstructive symptoms. Contrary to the bowel domain observations, urinary symptom rates did not differ significantly between SBRT and MH-IMRT groups, with respective MCID frequencies of 33.7% versus 34.7% (p=0.68). Despite this, secondary genitourinary metrics, including incontinence-related quality of life and erectile function maintenance, showed favorable trends with SBRT, highlighting its nuanced advantages in functional outcomes beyond primary endpoints.

Beyond quality-of-life measures, one of the pivotal co-primary endpoints was disease-free survival (DFS). The interim results of the study revealed that SBRT did not demonstrate superiority over hypofractionated IMRT in extending DFS at the three-year follow-up, with this co-primary endpoint crossing futility boundaries due to a higher rate of biochemical failure determined by prostate-specific antigen (PSA) levels in the SBRT arm. While this finding tempers expectations regarding SBRT’s oncologic superiority, it accentuates the necessity for prolonged follow-up to ascertain long-term efficacy beyond the current timeframe.

The trial’s findings dovetail with prior research, such as the PACE-B study, which established the non-inferiority of SBRT compared to conventional IMRT protocols. However, NRG-GU005 distinguishes itself by emphasizing patient-reported outcomes, underscoring the principle that therapeutic regimens must not only aim for tumor control but must also prioritize the preservation of patients’ quality of life during survivorship—a factor of immense importance in localized prostate cancer management where survival outcomes are generally favorable.

Notably, the improved bowel health outcomes observed with SBRT may be attributed to its precise, high-dose, hypofractionated delivery that minimizes radiation exposure to surrounding rectal tissues. Additionally, the use of rectal spacers during SBRT procedures further enhances tissue sparing, contributing to favorable quality-of-life metrics and affirming technical refinements’ role in optimizing radiation therapy’s therapeutic ratio.

The rigorous design of NRG-GU005 included serial administrations of EPIC-26 at critical intervals, securing high compliance rates—82.5% for MH-IMRT and 85.1% for SBRT at two years post-treatment. This robust data collection strengthens the confidence in these findings and provides a comprehensive picture of treatment-associated morbidity in a real-world clinical context. EPIC-26’s dual-domain evaluation of bowel and urinary health offers nuanced insights into subclinical and clinical symptom trajectories over time.

As Dr. Rodney J. Ellis from the University of South Florida, lead author of the NRG-GU005 abstract, noted, the trial’s findings substantiate SBRT as a compelling option that balances oncologic outcomes with patient-centered quality-of-life gains. While urinary irritation or obstruction did not significantly improve, the favorable secondary genitourinary endpoints suggest SBRT’s potential in mitigating other dimensions of treatment-related morbidity.

Equally crucial is the trial’s spotlight on the evolving paradigm of radiation fractionation in prostate cancer. Hypofractionated regimens like SBRT deliver a larger dose per fraction over fewer treatment sessions, offering logistical advantages such as reduced overall treatment time and improved resource utilization, which are increasingly relevant in busy oncology practices and for patient convenience.

Nonetheless, the absence of clear DFS superiority calls for cautious interpretation. While early biochemical recurrence may be higher, long-term oncologic outcomes remain the gold standard for treatment evaluation. Therefore, sustained longitudinal follow-up is imperative to fully characterize the risk-benefit balance and to ascertain whether the quality-of-life gains with SBRT can be maintained without compromising cancer control.

In light of these findings, clinical decision-making for localized intermediate-risk prostate cancer should integrate patient preferences, treatment logistics, potential side effect profiles, and long-term oncologic considerations. NRG-GU005 enriches the evidence base supporting SBRT as a viable and potentially preferred treatment option, especially for patients prioritizing bowel health and overall quality of life without sacrificing efficacy.

Funding for NRG-GU005 was robust, sourced from several National Cancer Institute grants, reflecting the collaborative effort between the NRG Oncology research network and federal agencies committed to advancing prostate cancer therapeutics. This level of investment underscores the critical importance placed on refining radiation modalities to optimize outcomes for patients worldwide.

The broader implications of this study resonate profoundly within clinical oncology, as the balance between treatment efficacy and quality of life becomes increasingly central to therapeutic strategies. NRG-GU005’s findings are expected to influence clinical guidelines, radiation oncology practices, and patient consultations, fostering a more nuanced, patient-centric approach to prostate cancer treatment in the modern era.

For those eager to delve deeper, a special episode of the NRG Oncology Podcast features an in-depth discussion with Dr. Rodney Ellis on the trial’s results and their clinical significance. Available across platforms such as Spotify, Apple Podcasts, and YouTube, this podcast serves as a valuable educational resource for clinicians, researchers, and patients alike.

In summary, the NRG-GU005 trial represents a landmark step forward in evaluating radiation strategies for intermediate-risk prostate cancer. By conclusively demonstrating that SBRT can improve bowel-related quality of life without compromising short-term disease control, this research propels SBRT into a favored position in the therapeutic armamentarium—heralding a future where precision radiation delivers not only cure but also compassionate, patient-centered care.

Subject of Research:
Localized intermediate-risk prostate cancer treatment outcomes comparing SBRT and hypofractionated IMRT.

Article Title:
Primary results from NRG-GU005: A Phase III Trial of SBRT vs. Hypofractionated IMRT for Localized Intermediate Risk Prostate Cancer.

News Publication Date:
September-October 2025.

Web References:

• NRG Oncology Podcast
• Spotify
• Apple Podcasts
• YouTube Podcast Channel
• NRG Oncology Official Website

References:
Ellis RJ, Pugh SL, Yu JB, Feng FY, Konski AA, Grubb III RL, Wallace RE, Gladstone DJ, Ménard C, Frazier AJ, Pennington JD, Michalski JM, Spratt DE, Martinez A, Morgan SC, Mihai A, Paulus R, Sander HM. Primary results from NRG-GU005: A Phase III Trial of SBRT vs. Hypofractionated IMRT for Localized Intermediate Risk Prostate Cancer. Paper presented during the Plenary Session at the American Society for Radiation Oncology Annual Meeting, San Francisco, CA, 2025.

Keywords:
Prostate cancer, stereotactic body radiation therapy, hypofractionated intensity-modulated radiation therapy, radiation therapy, quality of life, patient-reported outcomes, EPIC-26, bowel health, urinary symptoms, disease-free survival, clinical trial, NRG-GU005, radiation oncology.