S1026
Clinical – Paediatric tumours
ESTRO 2026
Digital Poster 4694
metastases. Material/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 BED ₁₀ and EQD ₂ were 37.5 Gy (31.25–72) and 31.2 Gy (31.2–60), respectively.The median PTV volume was 68 cm ³ (range, 2.1–541 cm ³ ). 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 RT. Further studies are warranted to establish the optimal SBRT dose and fractionation parameters for pediatric malignancies. References: 1. Tinkle CL, Singh C, Hyun JW, et al. Stereotactic body radiotherapy for metastatic and recurrent lesions in pediatric patients. Int J Radiat Oncol Biol Phys. 2020;99(5):E572. 2. Singh R, Bishop S, Jenkins J, et al. Stereotactic ablative radiation therapy (SABR) for adolescent and young adult malignancies: early outcomes and safety data. Cureus. 2024;16(8):e66890. 3. Tsang DS, et al. Stereotactic radiation therapy in children and young adults. Int J Radiat Oncol Biol Phys. 2025; (in press). Keywords: Pediatric Cancers, Stereotactic Body Radiotherapy
Irradiation of Pediatric Diffuse Intrinsic Pontine Gliomas (DIPG): Clinical and Radiological Response to Radiotherapy and Impact on Overall Survival. Carmen Colomina Molina 1 , María Sanchez Robles 2 , Ines Ollinger Casin 2 , Julia García Martínez 2 , Patricia Cabrera Roldan 2 1 Radiation Oncology, Hospital Virgen del Rocio, Sevilla, Spain. 2 Radiation Oncology, Hospital Virgen del Rocio, Seville, Spain Purpose/Objective: Radiotherapy (RT) remains the standard of care for DIPG, offering transient symptom control andmodest survival benefit. Early clinical and radiological response following RT has been proposed as apotential prognostic indicator, although data remain limited. This retrospective study experience with radiation therapy at a tertiary center examining the early clinical or radiologicalreviews ourresponse after RT and whether it correlates with overall survival (OS). Material/Methods: This retrospective study included 18 pediatric patients diagnosed with DIPG and treated with RT atour institution between 2017 and 2025. Survival was calculated from the date of radiologicaldiagnosis to the final event (death) or last follow-up, expressed in months. Clinical and radiologicalresponse post-RT were categorized as improvement, stable, or worse (clinical), and response, stabledisease, or no response/not performed (radiological, based on RECIST-like criteria). Due to thelimited number of non- responders, the analysis was descriptive, complemented by Kaplan–Meiersurvival estimation and log-rank testing. Survival probabilities at 6 and 12 months were computed,and median survival was compared across response categories. Results: Among 18 pediatric DIPG patients, median age was 6.5 years. Clinical improvement post-RToccurred in 94.4% (17/18), and radiological response in 61.1% (11/18). Median overall survival fromdiagnosis was 12.8 months (mean 14.1). Estimated survival rates were 88.2% at 6 months and 56.7%at 12 months. Log-rank tests showed no significant OS differences between clinical or radiologicalresponse groups.Radiotherapy achieved high symptomatic control, consistent with previous DIPG data showingtransient clinical benefit but limited survival extension. The absence of statistical association betweenearly response and survival likely reflects the small cohort size and response imbalance. Despite theselimitations, the findings reinforce the consistent palliative value of RT and the need for larger,multicenter standardized studies.
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