The potential of 4π radiotherapy: a new era for improving outcomes in challenging paediatric cases? A comparative dosimetric analysis

Introduction: 4π 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 4π radiotherapy compared to standard approaches, with particular emphasis on integral dose and OAR sparing. Materials and 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 4π plan was generated using five non-coplanar partial arcs. All patients received 54 Gy in 30 fractions (1.8 Gy/fraction). Dosimetric comparisons were made between original and 4π plans, focusing on mean doses to critical OARs and integral dose metrics. Results: The 4π 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 4π plans were clinically deliverable, with a modest increase in treatment time (~3 minutes) offset by improved precision. Conclusions: 4π 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.