Clinical Outcomes and Toxicity After Extracranial Stereotactic Body Radiotherapy for Pediatric Malignancies in a Two Center Retrospective Study

Background Stereotactic body radiotherapy (SBRT) in pediatric malignancies offers precise, high-dose radiation delivery to tumors while minimizing exposure to surrounding healthy tissues—an important consideration in preventing adverse effects on growth and development. The use of SBRT in pediatric oncology has been increasing; however, clinical data and outcome reports remain limited. This study aimed to evaluate local control (LC), progression-free survival (PFS), overall survival (OS), and toxicity rates following SBRT in pediatric patients with extracranial metastases. Materials/Methods Between 2012 and 2024, 21 pediatric patients treated in our department for extracranial lesions of malignant tumors using linear accelerator–based, CT-guided SBRT were retrospectively analyzed. LC and OS were assessed using the Kaplan–Meier method. Results All patients received definitive SBRT for oligometastatic disease. At diagnosis, 13 patients (61.9%) presented with metastatic disease. The median follow-up time was 10 months (range, 4–157), and the median age was 13 years (range, 4–17). Ewing sarcoma was the most common histologic subtype (52.4%). A total of 37 extracranial lesions were irradiated; 21 (56.7%) were bone metastases. SBRT was delivered to four sites in one patient and to three simultaneous sites in five patients.The median number of fractions was 5 (range, 3–5), with a median dose per fraction of 5 Gy (range, 5–9 Gy). Median BED₁₀and EQD₂were 37.5 Gy (31.25–72) and 31.2 Gy (31.2–60), respectively. The median PTV volume was 68 cm³ (range, 2.1–541 cm³). Median PFS was 8 ± 1.29 months (95% CI: 5.4–10.5), and median OS was 12 ± 3.07 months (95% CI: 5.98–18).Local recurrence occurred in 10 patients (47.6%), of whom 6 (60%) had in-field recurrences. Among these, 3 of 6 patients had osteosarcoma histology. One- and two-year LC rates were 25% and 18%, respectively, while OS rates were 49% and 30%. There was a statistically significant difference in both PFS and OS among histologic subtypes (p = 0.03 and p = 0.004, respectively). No ≥Grade 3 acute or late toxicity was observed. Conclusion SBRT was well tolerated in pediatric patients, with minimal toxicity. However, longer follow-up is required to assess late effects. The preference for more moderate fractionation schemes due to large tumor volumes and younger age groups may also be related to higher rates of in-field recurrence in histologies that are more resistant to radiotherapy. Further studies are warranted to establish the optimal SBRT dose and fractionation parameters for pediatric malignancies.