Postoperative Proton Beam Therapy for Intracranial Mesenchymal Tumors: Clinical Outcomes and Literature Review

Background: Central nervous system (CNS) mesenchymal tumors are a rare and diverse group of neoplasms with significant treatment challenges and often aggressive behavior. Standard management involves surgery followed by radiotherapy, but achieving local control without significant toxicity is difficult, especially in pediatric and young adult patients. Proton beam therapy (PBT) offers dosimetric advantages that may reduce treatment-related morbidity. This study evaluates the initial clinical outcomes of postoperative PBT for patients with these rare tumors. Methods: We retrospectively reviewed the records of nine patients (median age 14 years; range 4–43) with histologically confirmed intracranial mesenchymal tumors treated with postoperative PBT between June 2023 and February 2025. The cohort included various rare subtypes. All patients received pencil beam scanning PBT. Endpoints were overall survival (OS), local control (LC), and treatment-related toxicities graded via CTCAE v5.0. Survival rates were calculated using the Kaplan-Meier method. Results: The median follow-up was 8.7 months. The estimated 1-year OS rate was 77.8%, and the 1-year LC rate was 66.7%. Two deaths occurred, both due to disease progression. Three of nine patients experienced tumor progression. Acute toxicities were generally mild to moderate (Grade 1-2), including skin reactions, alopecia, and manageable hematologic effects primarily in patients receiving concurrent chemotherapy. No Grade 4 or 5 treatment-related toxicities were observed. No severe late toxicities were reported within the follow-up period. Conclusions: Postoperative PBT is a feasible treatment for CNS mesenchymal tumors, demonstrating encouraging initial efficacy and a manageable acute toxicity profile in this small, heterogeneous cohort. While limited by sample size and short follow-up, these findings support PBT as a valuable modality, particularly for minimizing radiation dose to healthy tissue in younger patients. Longer-term, multi-institutional studies are needed to confirm these results and optimize treatment strategies. Trial registration: This study was retrospectively registered.