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Stereotactic Intensity-modulated Radiotherapy After Radical Prostatectomy (SCIMITAR): 4-Year Outcomes of a Phase 2
Amar U Kishan1, Jesus E Juarez Casillas2, Paul Sargos3
1Department of Radiation Oncology, University of California-Los Angeles, Los Angeles, CA, USA; Department of Urology, University of California-Los Angeles, Los Angeles, CA, USA.
European Urology
|October 1, 2025
Summary
Stereotactic body radiotherapy (SBRT) shows promise for prostate cancer patients after surgery, offering effective biochemical recurrence-free survival. This advanced radiotherapy technique appears safe and beneficial for select patients up to four years post-treatment.
Area of Science:
- Oncology
- Radiation Oncology
- Clinical Trials
Background:
- Post-prostatectomy radiotherapy is crucial for patients with high-risk features.
- Stereotactic body radiotherapy (SBRT) offers a hypofractionated approach.
- Comparing SBRT to conventional fractionation (CFRT) in the adjuvant setting is important.
Purpose of the Study:
- To evaluate the efficacy and safety of SBRT to the prostatic fossa after radical prostatectomy.
- To compare SBRT outcomes with individual patient data (IPD) from a conventionally fractionated RT trial.
- To assess biochemical recurrence-free survival (BCR-FS) and toxicity profiles.
Main Methods:
- Phase 2 SCIMITAR trial involving 100 patients receiving SBRT (30-34 Gy/5 fractions).
- Comparison with IPD from a phase 3 CFRT trial using inverse probability of treatment weighting and Fine-Gray models.
- Primary endpoint: 4-year BCR-FS; secondary endpoints: toxicity and quality of life.
Main Results:
- The 4-year BCR-FS rate was 60%.
- SBRT showed a lower BCR risk compared to CFRT in patients not receiving ADT (sHR 0.49, p=0.008).
- No significant difference in BCR risk was observed between SBRT and CFRT in patients receiving ADT (sHR 1.58, p=0.18).
- Late grade ≥2 GI and GU toxicities at 4 years were 6.6% and 32%, respectively.
- Patient-reported outcomes showed varying impacts across urinary, bowel, and sexual domains.
Conclusions:
- SBRT to the prostatic fossa appears safe and effective for select post-prostatectomy patients up to 4 years.
- SBRT may be particularly beneficial for patients not receiving androgen deprivation therapy.
- Further investigation is warranted for patients receiving ADT to clarify BCR risk.
