Stereotactic ablative radiotherapy for oligometastatic prostate cancer

Background: The present study assessed clinical outcomes of stereotactic body radiotherapy (SBRT) in oligometastatic prostate cancer patients. Materials and methods: Between 2017 and 2020, 37 lesions (12 osseous and 25 nodal targets) detected with conventional and/or functional imaging, were treated in 29 patients (pts), in different clinical settings: de novo oligometastatic (2 pts), oligorecurrent castration-sensitive (19 pts), castration-resistant (6 pts) prostate cancers and oligoprogressive disease during systemic therapy (2 pts). SBRT was delivered with volumetric modulated arc therapy up to a total dose of 21 Gy given in 3 fractions for bone and 30 Gy in 5 fractions for nodal metastases. A total of 34% of pts received hormonal therapy. We evaluated biochemical control [prostate serum antigen (PSA) increase < 10%)], progression free-survival (PFS) (time from SBRT to biochemical progression), local control (LC) (time from SBRT to in-field radiologic progression), hormone/systemic therapy-free survival, acute and late toxicities. Results: At 3 months, biochemical response was observed in 20/29 pts (69%). At a median follow-up of 17 months (range 6-33), 8/20 (40%) of the 3-month responders remained free from progression. Two-year PFS and LC were 37% and 70%, respectively. In-field progression occurred in 3/37 (8%) lesions. Hormone/systemic therapy was delayed by an average of 11.6 months (range 3-28). No significant difference in PFS based on the type of lesion or concomitant endocrine therapy was observed and no toxicity > grade 2 was reported. Conclusions: SBRT for oligometastatic prostate cancer offers a good biochemical/local control and tangible delay of hormone/systemic therapy without major toxicities.