S1005
Clinical – Paediatric tumours
ESTRO 2026
raises age-specific dilemmas, including the risk of late effects, and presents technical challenges related to dose accumulation and radiotherapy planning in growing patients. This study aimed to quantify and describe a population-based cohort of paediatric patients offered reirradiation between 2008 and 2024. Material/Methods: Data were extracted from the Danish Childhood Cancer Registry and its radiotherapy sub-registry for 2008–2024, which includes all Danish children treated with radiotherapy. The sub-registry contains treatment technique, fractionation, and dose per course and fraction. Reirradiation data included anatomical overlap (yes/no/unknown) and treatment dates, but not accumulated doses. Patients under 18 at diagnosis who received radiotherapy were included = 557. Descriptive analyses were performed using RStudio. Results: A total of 102 paediatric patients underwent reirradiation ( ≈ 18%), corresponding to 152 treatment courses. Reirradiation was administered throughout the study period, peaking in 2020–2021 (Figure 1). Figure 2 shows diagnoses across five age groups for both first and reirradiation treatments. Brain tumours, followed by bone tumours, were most commonly reirradiated. Across 152 courses, there were 157 treatment targets (some treatments had multiple targets): 73 overlapped anatomically, 69 did not, and 10 were unknown. Mean dose in the previous treatment was 42 Gy for overlapping and 40 Gy for non-overlapping targets. For second treatments, median total dose was 25 Gy (range 1–66 Gy), median fraction dose 2 Gy/F (range 1–22), and median number of fractions 10 F (range 1–36). For ≥ 3rd treatments, they were mainly stereotactic (18 Gy/1 F), single-shot (8 Gy/1 F), or hypofractionated (25 Gy/5 F). Median time between treatments: treatment 1–2 = 1 y 2 m (2.5 m–9 y), treatment 2–3 = 11 m (0–5 y 3 m), treatment 3– 4 = 2 m (1–5 m). Conclusion: This population-based cohort includes all Danish children treated with radiotherapy and maps paediatric reirradiation in Denmark. It identifies children as a clinically relevant population frequently offered reirradiation, with some receiving multiple treatments, including stereotactic or single-fraction treatments. Variable intervals between treatments illustrate challenges of treating growing bones and tissues. These findings suggest that reirradiation in paediatric oncology may serve both life-prolonging and palliative purposes.Figure 1:
Figure 2
References: Figure 1 Number of reirradiation courses
(=treatments) given over time (years) (only data until April 2025). Figure 2 Distribution of diagnoses in 5 age groups. Colours indicates diagnoses and total number of patients are written in the stacked bar plot. Treatments are named courses in the plot. A: Course 1, B: All reirradiation courses, C: Only second course of
RT, D: Only 3rd course of RT, E: Course ≥ 3. Keywords: Reirradiation, national cohort
Digital Poster 1509 Clinical results of a hybrid combined proton and X- ray patch-field craniospinal irradiation for pediatric patients with medulloblastoma. Takeshi Fujisawa, Masashi Mizumoto, Takashi Saito, Haruko Numajiri, Masahiko Harada, Masaaki Goto, Takuya Sawada, Keiichiro Baba, Kei Nakamura, Takashi
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