S1021
Clinical – Paediatric tumours
ESTRO 2026
1 Department of Proton Beam Therapy, The Christie NHS Foundation Trust, Manchester, United Kingdom. 2 Division of Cancer Sciences, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom. 3 Patrick G Johnston Centre for Cancer Research, Queen’s University Belfast, Belfast, United Kingdom. 4 Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom Purpose/Objective: Cardiac side effects are a concern in children and young adults (CYA) receiving thoracic radiotherapy. An increased risk has been associated with mean heart dose (MHD) above10 Gy; however, this evidence relies on reconstructed data from older techniques1. To reduce cardiac side effects, we must first understand the cardiac doses delivered with contemporary (CT- based) radiotherapy. This systematic review summarises reported doses to the heart and its substructures in CYA patients treated with contemporary radiotherapy. Material/Methods: MEDLINE and EMBASE were systematically searched (2004–2024) for studies reporting cardiac doses in patients aged ≤ 25 years treated with CT-based radiotherapy. Studies relying on reconstructed or two- dimensional planning data were excluded. Mixed-age cohorts were included if CYA data constituted a substantial subgroup or were reported separately. Random-effects meta-analysis (Stata v19) was used to pool data. Results: Of 1258 records screened, 33 studies met inclusion criteria, representing 38 cohorts and 83 radiotherapy regimens from 11 countries (55.3% USA) between 2002–2022. In total, 838 plans were analysed; 736 contributed to pooled synthesis and 469 to MHD analysis. mean heart dose (MHD) analysis. Median age ranged 3–27 years, and prescribed doses 12.0–50.4 Gy. Lymphoma (333/838) followed by medulloblastoma (184/838) were the most common diagnosis.Photon and proton data were available for 60 and 23 regimens, respectively. MHD was reported in 39/83 regimens, followed by V5–V30 parameters. Cardiac substructure doses were available in 23 regimens [left ventricle (15/83), right coronary artery (15/83), and left main coronary artery (13/83)].Pooled MHD was 10.5 Gy (95% CI 9.0–12.0) for photons (Figure 1) and 5.4 Gy [RBE] (95% CI 3.5–7.2) for protons (p < 0.001; Qb = 17.4) (Figure 2). Among photon techniques (3DCRT, IMRT, VMAT, tomotherapy), MHD did not differ significantly, whereas within proton modalities, pencil beam scanning achieved the lowest doses (p < 0.001; Qb = 19.6). Between-study heterogeneity was high (I ² > 90%), possibly reflecting diagnostic variability.Few studies reported using heart contouring
guidelines and only 16 studies described cardiac outcomes, with inconsistent methodology.
Conclusion: Contemporary radiotherapy studies show wide variability in cardiac doses across modalities. Higher MHD in contemporary photon studies (10.5 Gy) compared with CCSS estimates (<5 Gy in 59% of cases),
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