S1009
Clinical – Paediatric tumours
ESTRO 2026
diagnosis was 0.6 years (range:0-11.7 years). Bilateral disease was present in 77.0% and 66.7% of the proton and photon cohorts, respectively (p=0.343). Family history of retinoblastoma was identified in 24.6% and 11.1% of proton and photon patients, respectively (p=0.121). Median follow up time was 16.7 years (range:0.1-34.4) and 28.5 years (range:1.4-43.9) in the proton and photon cohorts, respectively. Cumulative incidence of in-field SMN at 15 years was 0% and 13.7% in the proton and photon cohorts, respectively (p=0.007). Six patients had in-field SMNs after a median of 10.1 years after RT (range:4.9-27.9) and histologies included osteosarcoma (n=3), leiomyosarcoma (n=1), undifferentiated sarcoma (n=1), and glioblastoma (n=1). Of these patients, 4 died of SMN, 1 is without disease, and 1 was lost to follow up. OS at 15 years was 97.3% and 93.1% in the proton and photon cohorts, respectively (p=0.162). On UVA, in-field SMN was associated with decreased OS (HR 20.89, p=0.001). Conclusion: The risk of in-field SMN is associated with decreased survival and is significantly lower in patients with retinoblastoma treated with proton RT as opposed to photon RT, suggesting that when available and radiotherapy is indicated, proton RT should be favored. Late SMNs can occur and long-term follow-up remains important. Keywords: retinoblastoma, second malignancy, proton v photon Toward Implementation of Adaptive Radiotherapy in Paediatric Clinical Trials: A QUARTET Report on On-Treatment Imaging Practice and Replanning Maria Chiara Lo Greco 1,2 , Sarah M. Kelly 1,2 , Coreen Corning 3 , Stephanie L. E. Bolle 4 , Alison L. Cameron 5 , Raquel Dávila Fajardo 6 , Mark N. Gaze 7 , Anne Laprie 8 , Henriette Magelssen 9 , Enrica Seravalli 6 , Bob Smulders 10,11 , Andrada Turcas 12,13 , Amos Burke 14 , Julia Chisholm 15 , Habiba Lynda Attalah 16 , Claudia Pasqualini 17 , Tom Boterberg 18,2 , Henry C. Mandeville 7,15 1 QUARTET project, European Society for Paediatric Oncology, Brussels, Belgium. 2 Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium. 3 Medical Department, The European Organisation for Research and Treatment of Cancer (EORTC) Headquarters, Brussels, Belgium. 4 Oncología Radioterápica, Quirónsalud Proton Therapy Centre, Madrid, Spain. 5 Bristol Haematology and Oncology Centre, University Hospitals Bristol and Weston NHS Foundation Trust, Bristol, United Kingdom. 6 Department of Radiation Oncology, University Medical Centre Utrecht, Utrecht, Netherlands. 7 Department of Oncology, University College London Digital Poster Highlight 2401
Proffered Paper 2391 Proton radiatiotherapy decreases radiation- associated second malignant neoplasms compared to photon radiatiotherapy in patients with retinoblastoma Sayeh Fattahi 1 , Daniel G Packard 2 , Roshan V Sethi 3 , Helen A Shih 4 , Myrsini Ioakeim Ioannidou 4 , Efren Gonzalez 5 , Eric F Grabowski 6 , Junne Kamihara 7,8 , Torunn I Yock 4 , Nancy J Tarbell 4 , Karen J Marcus 3,9 , Shizuo Mukai 10 , Shannon M MacDonald 11 , Kevin X Liu 3,4 1 Radiation Oncology, Harvard Radiation Oncology Program, Boston, USA. 2 Internal Medicine, Mayo Clinic, Rochester, USA. 3 Radiation Oncology, Brigham and Women's Hospital/Dana-Farber Cancer Institute, Boston, USA. 4 Radiation Oncology, Massachusetts General Hospital, Boston, USA. 5 Ophthalmology, Boston Children's Hospital, Boston, USA. 6 Pediatric Hematology/Oncology, Massachusetts General Hospital, Boston, USA. 7 Pediatric Hematology/Oncology, Brigham and Women's Hospital/Dana-Farber Cancer Institute, Boston, USA. 8 Pediatric Hematology/Oncology, Boston Children's Hospital, Boston, USA. 9 Radiation Oncology, Boston Children's Hospital, Boston, USA. 10 Ophthalmology, Massachusetts Eye and Ear Institute, Boston, USA. 11 Radiation Oncology, Southwest Florida Proton, Fort Myers, USA Purpose/Objective: Retinoblastoma is the most common pediatric ocular neoplasm. The leading cause of death is second malignant neoplasm (SMN), the risk of which is increased in patients with hereditary retinoblastoma. There remains limited data regarding the benefit of proton radiation therapy (RT) over photon RT in modern cohorts. We aim to compare the incidence of in-field SMN and survival among patients with retinoblastoma treated with proton and photon RT. Material/Methods: This study was approved by the Institutional Review Board. All patients diagnosed with retinoblastoma between 1979-2019 and treated with RT at two major tertiary centers were identified. Clinical and treatment characteristics were extracted from paper and electronic medical records. Location of SMNs was reviewed with respect to the radiation field and any overlap with ≥ 50% of the prescription dose was considered in-field. Follow-up was defined from start of RT. Cumulative incidence of in-field SMN was reported with death as a competing risk and Gray’s test. Overall survival (OS) was estimated using the Kaplan-Meier method. Univariate analysis (UVA) was performed using Cox regression model. Results: We identified 97 patients; 62.9% were treated with proton RT and 37.1% with photon RT. Median age at
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