Physician-scored toxicity and patient-reported outcomes showed SBRT is well-tolerated post-prostatectomy.
Postoperative radiation therapy (RT) is an underutilized standard of care intervention for prostate cancer patients with recurrence/adverse pathologic features following radical prostatectomy. Although stereotactic body radiation therapy (SBRT) is a well-researched and convenient alternative for definitive treatment, data on its use after prostatectomy are exceedingly limited.
This study was published in the International Journal of Radiation Oncology, Biology, Physics and aimed to examine short-term genitourinary (GU) and gastrointestinal (GI) toxicity and patient-reported outcomes following post-prostatectomy SBRT.
The SCIMITAR experiment was a phase 2, dual-center, open-label, single-arm trial in which patients with postoperative prostate-specific antigen levels >0.03 ng/mL or unfavorable pathologic characteristics were included. Four-year biochemical recurrence-free survival, physician-scored acute and late GU and GI toxicities by the Common Terminology Criteria for Adverse Events scale, and patient-reported quality-of-life (QOL) outcomes, as measured by the Expanded Prostate Cancer Index-26 and the International Prostate Symptom Score, were co-primary endpoints. Patients underwent SBRT 30 to 34 Gy/5 fractions to the prostate bed to enhance pelvic nodes under the guidance of computed tomography (CTgRT) or magnetic resonance imaging (MRgRT). Physician-rated toxicity and patient-reported QOL outcomes were gathered at baseline and 1, 3, and 6 months after treatment initiation. Using univariable and multivariable analysis, predictors of toxicities and QOL outcomes were evaluated.
One hundred participants were enrolled (n = 69 for CTgRT and n = 31 for MRgRT). The median duration of follow-up was 29.5 months (CTgRT: 33.3 months, MRgRT: 22.6 months). The mean (range) dosage to the prostate bed was 32 (30-34) Gy. Acute and late grade 2 GU toxicities accounted for 9%, whereas acute and late grade 2 GI toxicities accounted for 5% and 0%, respectively. Three individuals experienced toxicity of grade 3 (n = 1 GU, 2 GI). No patient receiving MRgRT experienced GU or GI toxicity of grade 3 or grade 2. MRgRT was related to a 30.5% (95% confidence range, 11.6%–49.5%) reduction in any grade of acute GI toxicity compared to CTgRT (P =0.006).
The study concluded that in the first six months following prostatectomy, SBRT was well tolerated based on both physician-scored toxicity and patient-reported outcomes. In comparison to CTgRT, MRgRT was linked with significantly reduced GI toxicity and greater preservation of bowel QOL.
Long-term follow-up and randomized trials comparing traditional fractionation or moderate hypofractionation with SBRT to further describe its safety and efficacy are needed. 
Ma, T. M., Ballas, L. K., Wilhalme, H., Sachdeva, A., Chong, N., Sharma, S., Yang, T., Basehart, V., Reiter, R. E., Saigal, C., Chamie, K., Litwin, M. S., Rettig, M. B., Nickols, N. G., Yoon, S. M., Smith, L., Gao, Y., Steinberg, M. L., Cao, M., & Kishan, A. U. (2023). Quality-of-Life Outcomes and Toxicity Profile Among Patients With Localized Prostate Cancer After Radical Prostatectomy Treated With Stereotactic Body Radiation: The SCIMITAR Multicenter Phase 2 Trial. International Journal of Radiation Oncology, Biology, Physics, 115(1), 142-152. https://doi.org/10.1016/j.ijrobp.2022.08.041