Long-term Outcomes Following Proton Therapy for Pediatric Low-grade Glioma of the Spine (LGGS)

Abstract

Objectives

Due to its rarity, no standard treatment guidelines exist for LGGS. Proton therapy (PT) offers an attractive modality to minimize toxicity. To date no clinical outcomes on PT in LGGS have been reported. Herein, we present a series of pediatric patients who received PT for progressive LGGS.

Methods

We identified 8 consecutive patients with non-metastatic LGGS treated with PT between 2012 and 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

The median age at diagnosis was 4 years. All patients underwent attempted resection. Pilocytic astrocytoma was the most common tumor histology (n=4). All patients developed recurrence/progression of disease prior to referral for PT, with 3 having ≥ 2 recurrences prior to referral. The median duration between initial surgery and PT was 4.4 years. The 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. Most patients (n=7) received between 45-50.4 CGE. Median follow up was 7.8 years. The 10-year KM estimates for LC, FFDM, FFP, and OS were 85%, 88%, 73%, and 55% respectively. One patient experienced malignant transformation and 2 developed pseudoprogression following PT. No pulmonary, gastrointestinal, or musculoskeletal toxicity was observed during or after PT. No patients had ≥ grade 3 radiation related adverse events.

Conclusions

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.