3482 - Long-Term Outcomes following Proton Therapy for Pediatric Spinal Low-Grade Glioma

R. J. Brisson¹, D. J. Indelicato², J. A. Bradley¹, P. R. Aldana³, D. Klawinski⁴, C. G. Morris¹, and R. Mailhot Vega¹; ¹Department of Radiation Oncology, University of Florida College of Medicine, Jacksonville, FL, ²Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, ³Department of Neurosurgery, University of Florida College of Medicine Jacksonville, Jacksonville, FL, ⁴Department of Pediatric Hematology/Oncology, Nemours Children’s Specialty Care, Jacksonville, FL

Purpose/Objective(s): Due to its rarity, no standard treatment guidelines exist for pediatric low-grade glioma of the spine (LGGS). Traditionally chemotherapy has been offered as first line therapy, despite limited long-term efficacy. Radiation therapy is often avoided or deferred due to the perceived morbidity of radiation exiting through the thoracic or abdominal viscera. Proton therapy (PT) theoretically eliminates this risk but to date there have been no clinical outcomes reported on PT in the treatment of LGGS. Herein, we present a series of pediatric patients who received PT for progressive LGGS. Materials/

Methods: We performed an IRB-approved prospective outcome study of 8 patients with non-metastatic LGGS treated with PT between June 2012 and July 2022. We utilized the cumulative incidence method to estimate local control (LC), freedom from distant metastases (FFDM), freedom from progression (FFP), and overall survival (OS). Treatment related toxicity was assessed according to the CTCAEv5.
Results: Median age at diagnosis was 4 years. The most common presenting symptoms at diagnosis were pain (87.5%) and weakness/paralysis (50%). All patients underwent initial biopsy or attempted resection. Pilocytic astrocytoma was the most common tumor histology (n=4). Four patients (50%) had 2 surgical procedures prior to PT. All patients developed recurrence/progression of disease prior to referral for PT, with 3 patients having = 2 recurrences prior to referral. Five patients received chemotherapy prior to referral for PT, with carboplatin + vincristine being the most commonly utilized regimen. Median duration between initial surgery and PT was 4.4 years. Median age at the start of PT was 8 years. Most patients (n=5) received PT as = third line treatment. Seven patients were treated with PT to the primary tumor. One patient with extensive disease received PT to the total spine + a boost to the gross disease. Most patients (n=7) received between 45-50.4 CGE. Seven patients were treated with double scatter PT and 1 patient received pencil beam scanning PT. Median follow up was 7.8 years. The 10-year Kaplan-Meier estimates for LC, FFDM, FFP, and OS were 85%, 88%, 73%, and 55% respectively. One patient experienced malignant transformation 6.8 years following 54 CGE for desmoplastic astrocytoma. Two patients developed pseudoprogression following PT, 1 resolving with steroids and 1 resolving without treatment. No pulmonary, gastrointestinal, or musculoskeletal toxicity was observed during or after PT. No patients had ³ grade 3 radiation related adverse events.
Conclusion: Despite negative selection bias, with many patients having multiple recurrences prior to referral for PT, our experience suggests PT for pediatric LGGS offers long-term disease control with limited acute and late side effects. The favorable therapeutic ratio of PT suggests it should be considered among first-line therapy in children with non-metastatic, unresectable LGGS.