Comparative proton and photon treatment plans in children treated for neuroblastoma.

Background and purpose: Neuroblastoma is the most common extracranial solid tumour in children. Radiotherapy is commonly part of the multimodal treatment for high-risk patients. The aim of this study is to analyse doses to organs at risk (OAR) in comparative proton and photon treatment plans for children treated for neuroblastoma and report side effects. Patient/material and methods: All children in Sweden treated with curative intent radiotherapy for abdominal neuroblastoma in 2017-2024 with comparative proton and photon treatment plans were retrospectively identified through a national registry (RADTOX), where data on side effects were collected. Doses to OAR were compared in each patient's proton and photon treatment plans.

Results: A total of 30 children with a median age of 45 months (range 11-150) were included. The low-dose spread was significantly lower in the proton compared to the photon treatment plans measured as Body V5Gy and V10Gy (p < 0.001). Furthermore, the mean doses to the bowel bag, kidneys, liver, pancreas, and spleen were significantly lower in the proton plans. The median follow-up was 14 months (1-61), and the 2-year overall survival was 75.3%. While acute radiotherapy related grade ≥ 2 side effects were experienced by 12 patients (40%), late side effects were experienced by 7 patients (13%). The most common side effects were haematological and from the upper gastrointestinal tract.

Interpretation: In selected cases, proton treatment can offer lower doses to OAR and less low-dose exposure compared to photon treatment in children treated for abdominal neuroblastoma. Whether this translates into a clinical benefit is currently unclear and should be evaluated in future studies.