SBRT may offer a safe alternative to CFRT after prostatectomy

Stereotactic body radiotherapy appears safe and demonstrated comparable patient-reported outcomes through 2 years compared with conventionally fractionated radiotherapy (CFRT) in men with a rising prostate-specific antigen (PSA) level after radical prostatectomy, according to data from a phase 2 SCIMITAR trial (NCT03541850) published in JAMA Oncology.¹

Amar U. Kishan, MD

“This approach could remove a major barrier to post-surgery radiation therapy,” explained senior author Amar U. Kishan, MD, executive vice chair of radiation oncology at the David Geffen School of Medicine at the University of California, Los Angeles (UCLA), in a news release on the findings.² “SBRT shortens treatment time, reduces health care costs, and may have biological advantages in targeting prostate cancer. UCLA has long been a pioneer in SBRT for treating patients who have not yet had surgery, and now with the SCIMITAR trial, we have the first phase 2 data in the world to support this treatment in men who have had surgery.”

The study compared outcomes of 100 men who received post-operative SBRT with 200 men who received post-operative CFRT. The study was non-randomized.

In the SBRT cohort, 25% of patients experienced late grade 2 genitourinary (GU) toxicity and 4% experienced late grade 3 GU toxicity. Further, 3% of patients each experienced late grade 2 and late grade 3 gastrointestinal (GI) toxicity. These rates were comparable to those seen in the CFRT cohort.

The data also showed that MRI-guided SBRT further reduced GU and GI toxicity.

“We attribute this difference to primarily the narrower planning margin (3mm vs 5mm), which in turn we were confident using because of the more accurate daily setup imaging and improved motion management with gating,” added Kishan, who is also an investigator in the UCLA Health Jonsson Comprehensive Cancer Center, in the news release.²

The investigators then evaluated the proportion of patients who achieved decrements in patient-reported outcome measures greater than 2x the threshold for minimal clinically important difference (2xMCID). In the SBRT arm, this metric was achieved in 38.9% (37 of 95) of patients for urinary incontinence, 17.9% (17 of 95) of patients for urinary irritation, and 34.1% (31 of 91) of patients for bowel function.

The authors also noted that, “Compared with the CFRT cohort, the adjusted odds ratio for patients receiving SBRT experiencing decrements more than 2-fold the MCID was 1.55 (95% CI, 0.87 to 2.76; P = .14) for urinary incontinence, 0.94 (95% CI, 0.46 to 1.94; P = .87) for urinary irritation, and 1.03 (95% CI, 0.57 to 1.84; P = .93) for bowel function.”

Overall, the phase 2, single-arm SCIMITAR trial included men with localized prostate cancer who had undergone radical prostatectomy. Patients enrolled in the trial received SBRT (n = 100) and CFRT (n = 200) across 2 clinical trial sites in the US. To be eligible for enrollment, patients needed to have a post-radical prostatectomy PSA level greater than 0.03 ng/mL or adverse pathologic features.

Patients in the SBRT arm received radiotherapy at 30 to 34 Gy in 5 fractions to the prostate bed. According to the authors, “Nodal irradiation, boost to gross disease, and/or hormonal therapy were delivered per physician discretion.”

The median age of participants in the SBRT arm was 68.5 years (IQR, 63.9 to 71.4 years). The median follow-up was 43 months (IQR, 37 to 53 months).

The primary outcome measures are physician-scored toxicity, patient-reported toxicity outcomes per EPIC-26 and International Prostate Symptom Score, and biochemical recurrence-free survival.

The study remains ongoing, with final completion anticipated for November 2026.³ Another study, the EXCALIBUR trial (NCT04915508), is also underway to provide additional data on the long-term impact of SBRT in these patients.

Michael L. Steinberg, MD

“This study is a crucial step toward making prostate cancer treatment more accessible to patients,” concluded study co-author Michael L. Steinberg, MD, professor and chair of radiation oncology at the David Geffen School of Medicine at UCLA and director of Clinical Affairs at the UCLA Health Jonsson Comprehensive Cancer Center, in the news release.² “We’re optimistic that shorter, more convenient radiation schedules will improve care and quality of life for men with prostate cancer.”

REFERENCES

1. Nikitas J, Ballas LK, Romero T, et al. Patient-reported outcomes with stereotactic intensity modulated radiotherapy after radical prostatectomy: A nonrandomized clinical trial. JAMA Oncol. 2025. doi:10.1001/jamaoncol.2025.1059

2. Shorter radiation therapy after prostate surgery safe, study finds. News release. University of California, Los Angeles (UCLA), Health Sciences. May 13, 2025. Accessed May 16, 2025. https://www.newswise.com/articles/shorter-radiation-therapy-after-prostate-surgery-safe-study-finds

3. Stereotactic body radiation therapy in treating patients with localized prostate cancer that have undergone surgery. ClinicalTrials.gov. Last updated September 19, 2024. Accessed May 16, 2025. https://clinicaltrials.gov/study/NCT03541850