Phase III Trial Shows Five-Treatment Radiation Regimen Improves Quality of Life for Prostate Cancer Patients

Men with intermediate-risk prostate cancer can now receive a complete course of radiation therapy in just five treatments while maintaining excellent cancer control and experiencing improved quality of life, according to results from the international NRG Oncology GU-005 phase III trial presented at the American Society for Radiation Oncology (ASTRO) Annual Meeting.

The study, led by Dr. Rodney J. Ellis from Tampa General Cancer Institute, represents one of the first large international phase III randomized trials directly comparing stereotactic body radiotherapy (SBRT) with longer-course moderately hypofractionated intensity-modulated radiation therapy (IMRT) for men with localized, intermediate-risk prostate cancer.

Trial Design and Patient Population

The multicenter trial enrolled 698 patients across six countries, randomly assigning them to receive either SBRT delivered in five highly targeted treatments over two weeks, or standard IMRT delivered in 20 to 28 sessions over four to six weeks. The study utilized co-primary endpoints of disease-free survival and patient-reported outcomes to comprehensively evaluate treatment effectiveness.

Superior Quality of Life Outcomes

Two years after treatment, men treated with SBRT demonstrated significantly better preservation of multiple quality-of-life measures compared to those receiving standard radiation therapy:

Bowel Function: Fewer SBRT patients reported clinically meaningful declines in bowel quality of life at two years (35% vs. 44%, p=0.034).

Sexual Function: SBRT patients experienced less decline in sexual function at one year (34.3% vs. 43.9%, p=0.026).

Urinary Control: SBRT patients had significantly better urinary incontinence scores at two years (25.9% vs. 34.7%, p=0.023).

"We demonstrated that patients treated with SBRT had fewer problems with urinary incontinence, better preservation of sexual function and significantly less rectal toxicity compared to those receiving longer-course radiation," Ellis explained.

Comparable Cancer Control

Three years after treatment, both treatment groups maintained high rates of disease-free survival, with 88.6% for SBRT patients compared to 92.1% for those receiving standard IMRT. Overall survival rates were similarly high at 91% versus 94%, respectively.

While SBRT patients showed a slightly higher rate of biochemical recurrence at three years (8% vs. 4%), Ellis emphasized that longer follow-up is needed to determine whether this difference reflects transient PSA "bounces" commonly seen after SBRT rather than true cancer recurrence.

Technical Precision Enables Better Outcomes

SBRT achieves its superior outcomes through advanced imaging, fiducial markers, and daily image guidance to deliver high doses of radiation directly to the prostate and cancerous lesions with millimeter precision. This targeted approach reduces exposure to nearby organs such as the rectum and bladder.

"The precision of modern SBRT is what makes this possible," Ellis explained. "By using daily imaging and careful dose constraints, we can safely escalate the dose to the tumor while protecting bowel and bladder function."

The GU-005 trial showed improved toxicity profiles compared to the previous PACE-B trial, likely due to stricter protocol requirements including mandatory MRI fusion and daily image guidance.

Clinical Impact and Implementation

Prostate cancer represents the most common solid tumor in men, with intermediate-risk prostate cancer accounting for a substantial proportion of new diagnoses in the United States. The five-treatment regimen reduces treatment time by more than 80% compared to traditional approaches, potentially benefiting tens of thousands of men annually.

"For patients, this means less time away from work and family, fewer side effects and a treatment that is just as effective as what we've done for decades," Ellis noted.

Dr. Abraham Schwarzberg, executive vice president and chief of Oncology at Tampa General Hospital, emphasized the broader implications: "The evidence is clear that we can shorten therapy, improve important aspects of quality of life and preserve outcomes — exactly the kind of change that patients value."

Future Standard of Care

The combination of GU-005 results with previous PACE-B trial data provides definitive phase III evidence supporting SBRT as a preferred treatment approach. Ellis expects the findings will quickly establish five-treatment SBRT as the standard of care for men with localized, intermediate-risk prostate cancer.

"With GU-005 and PACE-B together, we now have definitive, phase III evidence that five-treatment SBRT is safe, effective — and in many cases superior to longer regimens," Ellis concluded. "This will move forward recognition of SBRT as the preferred approach, and I expect it will quickly become the standard of care."