ESTRO 2025 - Abstract Book

S1652

Clinical – äediatric tumours

ESTRO 2025

Material/Methods: Between 2017 and 2024, 20 Austrian children (female 5, male 15) with the mean age of 12 years (range: 1-15) diagnosed with Ewing sarcoma received pencil beam scanning PT at MedAustron. All treatments were administered according to the Euro-Ewing 2008 protocol. Clinical and treatment-related data were collected, and acute and late toxicity incidences were graded according to CTCAE v5.1. The primary endpoint is to evaluate LC and the patterns of recurrence (in-field, out of field, and marginal), while the secondary endpoint assesses toxicity related to functional outcomes. The Kaplan-Meier method was used to estimate the LC. Results: Twenty patients were treated in definitive (7), adjuvant (7), or neoadjuvant (6) settings. The sites of treatment were the pelvis (12), thorax (3), spine (3), and craniofacial (2). Out of the total patients, 8 were diagnosed with stage IV disease, for which radiotherapy was delivered to the primary disease site. Median dose was 54 GyRBE (range: 45-60) at 1.8 GyRBE for fraction. Patients who received neoadjuvant therapy subsequently underwent completion surgery, with a total of 3 R0 and 3 R1 resections. The median Follow up was 36.5 months with a LC of 67.4%. Of the 6 patients who experienced local recurrence, 3 were classified as out of field, 1 as marginal and 1 as in-field. Four patients died due to metastatic disease, with the lungs being the most frequent location of metastases. No patients exhibited grade 3 toxicities; however, 3 patients with pelvic tumors experienced G2 mobility issues which is continues to improve over time.