S1006
Clinical – Paediatric tumours
ESTRO 2026
Keywords: medulloblastoma, proton, craniospinal irradiation
Iizumi, Taisuke Sumiya, Toshiki Ishida, Masatoshi Nakamura, Hideyuki Sakurai Radiation Oncology, Tsukuba university hospital, Tsukuba, Japan Purpose/Objective: Proton craniospinal irradiation (CSI) reduces the dose to surrounding tissues and the risk of secondary malignancies in children with medulloblastoma. However, in older proton therapy systems, the maximum field length is limited, making full craniospinal coverage technically challenging. To overcome this limitation, we adopted a hybrid approach combining X-ray whole-brain irradiation with proton spinal irradiation using multiple patch junctions. This multi-patch design was intended to minimize junctional dose inhomogeneity caused by setup or range uncertainty. This study retrospectively evaluated the clinical outcomes and failure patterns of this hybrid patch-field proton CSI technique. Material/Methods: We reviewed 16 consecutive patients treated postoperatively with hybrid proton CSI between December 2016 and December 2024. All patients underwent surgery followed by chemotherapy and radiotherapy. Whole-brain irradiation was delivered with X-rays, and whole-spinal cord irradiation was performed with protons. Multiple patch junctions were planned to achieve an accumulated junctional dose between 90% and 110% of the prescribed dose. Treatment outcomes, recurrence patterns (in the boost field, in the CSI field, or outside the field), overall survival (OS), and relapse-free survival (RFS) were analyzed. Results: The median age at diagnosis was 7 years (range: 4–11). Six patients had spinal dissemination at the time of diagnosis. Gross total resection was achieved in 12 patients, and all received adjuvant chemotherapy. The median prescribed CSI dose was 18 Gy (range: 18–36 Gy), and the median boost dose was 54 Gy (range: 50.4–54 Gy). During follow-up, three patients developed recurrence: one local, one intracranial dissemination, and one combined intracranial and spinal relapse. No recurrence occurred exclusively at the junction regions, indicating that junctional dose uncertainty did not lead to underdosage or treatment failure. Four-year OS and RFS were 83% (95% CI: 65– 100) and 76% (95% CI: 55–100), respectively. Conclusion: Hybrid patch-field CSI, combining X-ray and proton therapy with multiple junctions, achieved favorable local control without junction-related recurrence. This approach provides a practical and safe solution for facilities utilizing proton systems with limited field sizes, allowing for full craniospinal coverage without compromising clinical outcomes.
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Neurocognitive dose-response relationship following pediatric brain tumor radiotherapy Anneli Edvardsson 1,2 , Edvard De Fine Licht 3,4 , Jenny Gorgisyan 1,2 , Martin Nilsson 5 , Ingrid Fagerström Kristensen 5 , Ingrid Tonning Olsson 3,4 , Per Munck Af Rosenschöld 1,2 1 Radiation physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden. 2 Medical Radiation Physics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden. 3 Paediatrics, Skåne University Hospital, Lund, Sweden. 4 Paediatrics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden. 5 Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden Purpose/Objective: Cranial radiotherapy (RT), especially craniospinal irradiation (CSI), is associated with long-term neurocognitive complications in survivors of pediatric brain tumors (PBT), which may negatively impact academic achievement and social functioning. One commonly affected domain is cognitive processing speed (PS), which reflects the efficiency with which the brain perceives, interprets, and responds to information. The aim of this study was to investigate associations between cognitive PS and radiation dose to specific brain structures following PBT RT. Material/Methods: Forty-five PBT survivors who received photon and/or proton radiotherapy, either CSI or focal, and completed neuropsychological follow-up were included in this cross-sectional study. Mean age at treatment was 9.5±3.7 years and mean time from RT to follow-up was 3.4±1.7 years. The whole brain, brainstem, cerebrum, cerebellum, hippocampi, hypothalami, thalami, and frontal and temporal lobes were retrospectively and consistently delineated using MR images. Mean doses to the structures were calculated based on the delivered treatment plans. Cognitive PS was measured using age-appropriate Wechsler tests (Coding and Symbol Search) and converted to age-adjusted z-scores (mean=0, SD=1) using national norms. Impairment was defined as a z- score < − 1.5. Logistic regression models were used in SPSS to assess the effects of mean dose to brain substructures on PS impairment. Results: Cognitive PS impairment was noted in 35% of the patients as compared to the expected 7% in the general population. In univariate logistic regression,
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