Data support SBRT as alternative to CFRT in post-prostatectomy setting

Stereotactic body radiotherapy (SBRT) delivered to the prostate fossa and/or pelvic nodes after radical prostatectomy demonstrated favorable 4-year biochemical recurrence-free survival (BCRFS) with a manageable safety profile, according to data from the phase 2 SCIMITAR trial (NCT03541850), presented at the American Society for Radiation Oncology (ASTRO) 67th Annual Meeting in San Francisco, California.¹

The data were also concurrently published in European Urology.²

“These findings suggest this faster treatment approach could offer an alternative to conventional, longer radiation courses for men at risk of recurrent prostate cancer,” said co–first author Amar U. Kishan, MD, professor and executive vice chair of radiation oncology at the David Geffen School of Medicine at the University of California, Los Angeles (UCLA) and co-director of the cancer molecular imaging, nanotechnology and theranostics program at the UCLA Health Jonsson Comprehensive Cancer Center, in a news release on the findings.³ “Importantly, [adverse] effects were manageable in a majority of men, particularly with MRI-guided treatment, and most men were able to maintain their quality of life.”

In total, the trial included 100 patients who received 30 to 34 Gy in 5 fractions to the prostate bed with or without bed boost with or without pelvic nodes. Use of androgen deprivation therapy (ADT) and nodal therapy was at the discretion of the treating physician. The primary end point was 4-year BCRFS, with biochemical recurrence defined as a rise in the posttreatment nadir PSA of 0.2 ng/mL or more.

Data from the SCIMITAR trial were compared to a literature-based historical control group as well as to individual patient data (IPD) from the phase 3 GETUG-AFU 16 trial of conventionally fractionated salvage radiotherapy (CFRT) with or without 6 months of ADT. The median follow-up in the SCIMITAR trial was 52 months (IQR, 45 to 59).

Overall, 4% of patients (n = 4) experienced local recurrence, 14% (n = 14) had nodal recurrence, and 18% (n = 18) developed distant metastasis. The 4-year BCRFS was 60% (95% CI, 0.49 to 0.70), which, according to the authors, “was not significantly different from the literature-based historical control (P = .34).”

The cross-trial comparison with IPD showed that among patients not receiving ADT, SBRT was associated with a lower risk of BCR compared with CFRT (subdistribution HR [sHR], 0.49; 95% CI, 0.29 to 0.84; P = .008). Among those who received ADT, there was no significant difference in BCR risk between the SBRT and CFRT cohorts (sHR, 1.58; 95% CI, 0.81 to 3.11; P = .18). However, the authors noted that “the asymmetrically broad 95% CI and directionality of the point estimate suggest that a higher BCR risk with SBRT cannot be ruled out.”

The findings also showed that delivery of SBRT to the prostatic fossa was safe. Overall, late grade 2 or higher gastrointestinal and genitourinary (GU) toxicities occurred in 6.6% and 32% of patients, respectively, at 4 years. Data also showed that MRI guidance was associated with a further decrease in GU toxicity (sHR, 0.34; P = .045).

The authors also reported, “At 48 months, the proportion of patients reporting a decline of more than 2 times the minimal clinically important difference in urinary incontinence, urinary irritative/obstructive, bowel, and sexual domains was 23%, 6.7%, 13%, and 9.7%, respectively.”

Based on these findings, Jesus E. Juarez Casillas, MD, MS, concluded during the presentation at ASTRO, “This provides [the first] prospective phase 2 evidence supporting SBRT as an alternative to conventionally fractionated radiotherapy in the postprostatectomy setting. We also noted that MRI guidance further decreased GU toxicity. SBRT to the prostatic fossa was shown to be safe, effective, and efficient through 4 years.”

REFERENCES
1. Juarez Castillas JE, Sargos P, Romera T, et al. Stereotactic intensity modulated radiotherapy after radical prostatectomy (SCIMITAR): four-year outcomes of a phase II clinical trial. Presented at: American Society for Radiation Oncology 67th Annual Meeting; September 27-October 1, 2025; San Francisco, CA. Abstract 114.

2. Kishan AU, Juarez Casillas JE, Sargos P, et al. Stereotactic intensity-modulated radiotherapy after radical prostatectomy (SCIMITAR): 4-year outcomes of a phase 2 clinical trial. Eur Urol. Published online September 30, 2025. doi:10.1016/j.eururo.2025.09.4149

3. Short-course radiation therapy after prostate surgery helps keep cancer from returning. News release. University of California, Los Angeles (UCLA), Health Sciences. October 2, 2025. Accessed October 9, 2025. https://www.newswise.com/articles/short-course-radiation-therapy-after-prostate-surgery-helps-keep-cancer-from-returning