2569 - Evaluation of the Safety and Efficacy of Stereotactic Body Radiotherapy for Oligometastasis: Real-World Data from a Developing Country

G. N. Marta¹, F. Restini², D. M. F. Palhares², F. F. de Arruda¹, C. E. C. V. Abreu¹, W. F. P. Neves-Junior¹, L. H. Brito¹, F. H. Yoshimoto¹, C. F. P. M. de Sousa¹, M. D. C. Santos¹, J. L. F. Silva¹, A. Mancini¹, T. M. M. T. Alves¹, E. L. Pelosi¹, C. K. Haddad¹, J. P. S. Leite², E. S. Batalha Filho², G. S. M. D. Siqueira², R. Gadia², and S. A. Hanna¹; ¹Department of Radiation Oncology, Hospital Sírio-Libanês, Sao Paulo, Brazil, ²Department of Radiation Oncology, Hospital Sírio-Libanês, Brasília, Brazil

Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is a highly precise treatment technique that delivers high conformal doses per fraction. It has been commonly used to treat oligometastatic tumors due to promising results from randomized clinical trials. However, data on the efficacy and safety of delivering SBRT for oligometastatic lesions in developing countries is still lacking, and questions exist regarding how to select the best candidates for such treatment. Therefore, this study aims to assess the safety and efficacy of SBRT for metastatic disease using data derived from a large cohort in a developing country. Materials/

Methods: We retrospectively reviewed patients with solid primary malignancies (except small cell lung cancer) who underwent SBRT to extracranial metastasis with the primary intent of improving local control, between 2012 and 2022, from a single quaternary institution in Brazil. The primary outcome was local control (LC) and grade =3 toxicity, and secondary outcomes were progression-free survival (PFS) and overall survival (OS). The Kaplan-Meier method was utilized to estimate survival outcomes. Cox proportional hazards regression models were used to evaluate the relationship between survival outcomes and potential prognostic factors.
Results: A total of 539 patients were included (median age of 69.5 years, range 25.5 to 98.4). The most common primary sites were prostate (n = 122, 21.9%), lung (n = 82, 14.7%), breast (n = 75, 13.4%), and colon (n = 67, 12.0%). Most patients had de-novo metastatic disease (n = 378, 69.0%). The median follow-up was 13 months. The 3-year and 5-year LC rates were 97% and 94.8%, PFS rates were 73.4% and 59.7%, and OS rates were 97.5% and 96.1%, respectively. We identified that patients with 0-2 lesions targeted with SBRT, as opposed to =3 lesions, exhibited a significantly lower risk of recurrence (hazard ratio 0.68, 95% CI 0.525-0.886, p=0.004). Grade =3 adverse events were reported in only 3 patients (<1%), being gastrointestinal, hepatobiliary and musculoskeletal.
Conclusion: This study represents the largest cohort demonstrating the safety and efficacy of SBRT for the treatment of oligometastatic disease in Brazil. Ongoing analyses are expected to identify the subgroup of patients that derive the greatest benefit from treatment, which could aid in patient selection.