Prostate-directed Radiotherapy in Selected Patients With Metastatic Castration-sensitive Prostate Cancer: A Real-world Case Series

Background/Aim: Prostate-directed radiotherapy (RT) improves outcomes in selected patients with metastatic castration-sensitive prostate cancer (mCSPC), particularly those with low metastatic burden. However, real-world information regarding its use after response to systemic therapy remains limited. This study describes the treatment characteristics, safety, and clinical course of selected patients with mCSPC who received prostate-directed RT. Patients and Methods: We retrospectively reviewed an institutional RT database containing 396 patients who initiated prostate-directed RT between April 2015 and March 2026. Thirteen patients had mCSPC at RT initiation and were included. Prostate-directed RT was considered after a marked prostate-specific antigen (PSA) decline and confirmation of no radiographic progression during first-line systemic therapy; no prespecified PSA threshold was used. Patient characteristics, RT details, RT-related adverse events, and clinical outcomes after RT completion were evaluated. Results: Eight patients had low-volume and five had high-volume disease. The median interval from initiation of first-line systemic therapy to RT was 8.4 months. The median PSA decline before RT was 99.9% (interquartile range=98.9-99.9%), and the median PSA level before RT was 0.028 ng/ml. All patients received intensity-modulated RT, and residual metastatic lesions were included in the RT target volume in six patients. All patients completed RT. No grade ≥2 acute genitourinary or gastrointestinal toxicity was observed, and no late RT-related toxicity occurred among the 11 patients evaluable for late toxicity. During follow-up (median, 39.6 months) after RT, four patients developed castration-resistant disease and four experienced radiographic progression. No post-RT local events or prostate cancer-specific deaths occurred; one patient died of an unrelated cause. Conclusion: In this small, highly selected cohort of patients demonstrating favorable initial responses to systemic therapy, prostate-directed RT was feasible and well tolerated, with no grade ≥2 acute RT-related toxicity, no late toxicity among evaluable patients, and no local events. Comparative efficacy cannot be determined because of the retrospective design, small sample size, and absence of a non-RT control group.