RADT-77. PROTON RADIATION MAY BE ASSOCIATED WITH IMPROVED SURVIVAL IN PEDIATRIC AND ADOLESCENT/YOUNG ADULT PATIENTS WITH LOW-GRADE GLIOMA

Abstract INTRODUCTION Low-grade gliomas (LGGs) are slower growing tumors commonly diagnosed in younger patients. Radiotherapy (RT) is a treatment option for LGGs but commonly deferred in young patients because of toxicity concerns. Proton RT can offer reduced toxicity with comparable efficacy, but outcome data remain limited in pediatric (age ≤18) and adolescent/young adult (AYA) (age 15-39) patients with LGG. METHODS This study evaluated 26,911 pediatric/AYA patients (age 0-39) in the National Cancer Database diagnosed with LGG between 2004-2022. Kaplan-Meier analysis with log-rank test and multivariable Cox regression assessed impact of factors including RT modality on overall survival (OS). Chi-square analysis evaluated variables impacting treatment with proton versus photon RT. RESULTS RT was administered in 6,909 patients (26%), with a median age of 30 years (interquartile range: 24–35 years) and median OS of 145 months (95% CI: 137–152 months). Histologies included low-grade diffuse astrocytoma (50%), oligodendroglioma (20%), oligoastrocytoma (19%), and pilocytic astrocytoma (7.5%). Among RT recipients, 8% received proton RT, 71% received photon RT, and 21% had an unknown modality. Proton RT was more commonly utilized in pediatric vs. AYA patients (14.7% vs, 7.0%, p<0.001) and in patients with pilocytic astrocytoma/oligodendroglioma vs. diffuse astrocytoma/oligoastrocytoma (10.2% vs, 6.8%, p<0.001). On univariate analysis, proton RT, pilocytic astrocytoma/oligodendroglioma histology, smaller tumor size, and gross total resection (GTR) were associated with improved OS (p<0.001). On multivariate analysis all factors remain significant (p<0.001): proton RT, hazard ratio (HR) 0.59 (95% CI: 0.46-0.74); pilocytic astrocytoma/oligodendroglioma, HR 0.51 (95% CI: 0.46-0.56); tumor size >40 mm, HR 1.4 (95% CI: 1.2-1.5); GTR, HR 0.60 (95% CI: 0.53-0.68). CONCLUSION While potentially impacted by selection bias, proton RT may be associated with improved survival in pediatric and AYA LGG patients and warrants consideration in both these populations given current limited utilization in AYA patients.