Cell-free DNA methylation-based detection of organ damage following proton versus photon radiotherapy: a case series.

Rapid and accurate methods of assessing organ damage following radiation therapy (RT) in pediatric cancer patients represent a vital need. This is the pilot study that assesses critical organ damage during pediatric RT using cell-free DNA (cfDNA) methylation analysis, providing insights for future research on cfDNA methylation detection of organ damage and offering a method for rapid clinical detection of multi-organ injury. In this study, three pediatric patients with medulloblastoma, one with a germ cell tumor, one with a mixed germ cell tumor, and one with a neuroepithelial tumor were enrolled. They were divided by therapeutic intervention: two patients underwent conventional photon-based craniospinal irradiation (CSI), while four received proton therapy. One patient receiving photodynamic therapy experienced Grade 3 gastrointestinal toxicity during treatment. We measured the levels of fraction of cfDNA methylation in these patients before and after CSI with photon and proton RT. We then compared the trends in cell-free DNA methylation changes between proton and photon therapy with their respective dose distributions and clinical outcomes. cfDNA methylation trends correlated well with both the organ-specific dose profiles and clinical outcomes observed between proton and photon RT. A comparative analysis of pre-/post-CSI cfDNA methylation changes, clinical outcomes, dose volume histogram (DVH) data, and isodose distribution maps suggests that cfDNA methylation is expected to become a biomarker for detecting organ damage, and that proton therapy provides better critical organ protection than photon therapy in pediatric patients.