S1003
Clinical – Paediatric tumours
ESTRO 2026
were made between original and 4 π plans, focusing on mean doses to critical OARs and integral dose metrics.
the combined local therapy group and in 14/16 patients in the definitive PBT group, with 2 additional patients requiring permanent urinary diversion. Conclusion: PBT enables radiotherapy of pelvic RMS with low toxicity and favourable oncologic outcome, even in young children. Combined tumor resection and PBT appear to achieve higher survival rates than definitive PBT. Local treatment strategies should be decided in collaboration with radiation and surgical oncologists to improve oncologic outcomes and organ preservation rates. Keywords: Proton beam therapy, rhabdomyosarcoma, children The Potential of 4π Radiotherapy: A New Era for Improving Outcomes in Challenging Paediatric Cases? A Comparative Dosimetric Analysis Costanza M Donati 1,2 , Lidia Strigari 3 , Silvia Strolin 3 , Erika Galietta 1,2 , Arina A Zamfir 2 , Silvia Cammelli 1,2 , Fraia Melchionda 4 , Elena L Legnani 4 , Federico Mercolini 4 , Riccardo Masetti 4,1 , Alessio G Morganti 1,2 1 Department of Medical and Surgical Sciences (DIMEC), Alma Mater Studiorum University of Bologna, Bologna, Italy. 2 Radiation Oncology, IRCCS Azienda Ospedaliero- Universitaria di Bologna, Bologna, Italy. 3 Department Digital Poster 1334 of Medical Physics, IRCCS Azienda Ospedaliero- Universitaria di Bologna, Bologna, Italy. 4 Pediatric Hematology and Oncology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy Purpose/Objective: 4 π radiotherapy is an advanced technique that employs non-coplanar beam trajectories to enhance dose conformality and minimize irradiation to organs at risk (OARs). In pediatric neuro-oncology, conventional modalities such as VMAT and IMRT are widely adopted; however, reducing toxicity to developing healthy tissues remains a major clinical challenge. This study explores the dosimetric benefits of 4 π radiotherapy compared to standard approaches, with particular emphasis on integral dose and OAR sparing. Material/Methods: A retrospective analysis was conducted on ten pediatric patients treated with cranial radiotherapy between 2019 and 2025 using VMAT or IMRT. Diagnoses included ependymoma (n=4), medulloblastoma (n=2), high-grade glioma (n=2), and atypical teratoid/rhabdoid tumor (n=2), with patient ages ranging from 1 to 17 years. For each case, a novel 4 π plan was generated using five non-coplanar partial arcs (Figure 1). All patients received 54 Gy in 30 fractions (1.8 Gy/fraction). Dosimetric comparisons
Results: The 4 π technique demonstrated superior sparing of critical structures, with mean dose reductions ranging from 15% to 78% for the optic chiasm, optic nerves, hypothalamus, pituitary gland, hippocampi, and cochleae. Target coverage was more homogeneous, with a reduction in maximum dose within the planning target volume (PTV). Integral dose was comparable or reduced in all cases, suggesting a potential decrease in long-term toxicity and risk of secondary malignancies. All 4 π plans were clinically deliverable, with a modest increase in treatment time (~3 minutes) offset by improved precision. Conclusion: 4 π radiotherapy offers promising dosimetric advantages over conventional techniques in pediatric cranial irradiation. These findings support further investigation into its clinical application to improve therapeutic ratios and reduce late effects in vulnerable pediatric populations. Keywords: 4 π Radiotherapy, dosimetric analysis, paediatric The technological landscape of paediatric radiotherapy in Denmark from 2008 to 2024 Daniella Elisabet Østergaard 1 , Bob Smulders 1,2 , Morten Høyer 2 , Morten Jørgsensen 1 , Yasmin Lassen- Ramshad 2,3 , Akmal Safwat 2,3 , Lisa Lyngsie Hjalgrim 4 , Maja Vestmø Maraldo 1,5 1 Department of Oncology, University Hospital of Copenhagen – Rigshospitalet, Copenhagen, Denmark. 2 Danish Centre for Particle Therapy, University Hospital of Aarhus, Aarhus, Denmark. 3 Department of Oncology, University Hospital of Aarhus, Aarhus, Denmark. 4 Department of Children and Adolescent Medicine, University Hospital of Copenhagen – Rigshospitalet, Copenhagen, Denmark. 5 Department of Clinical Medicine, Faculty of Health, University of Copenhagen, Copenhagen, Denmark Digital Poster Highlight 1381
Purpose/Objective: Survival rates in paediatric cancer have increased
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