Proton radiotherapy for glioma and glioblastoma

Radiotherapy (RT) continues to be an important component of treatment of glioma, particularly high-grade glioma and glioblastoma multiforme (GBM). GBM is one of the most aggressive central nervous system (CNS) tumors, with high rates of recurrence and very low rates of long-term survival. However, outcomes in these patients are improving with modern genetic profiling and multimodal therapy, which leads to more consideration for the risk for toxicities associated with traditional photon-based RT. Proton therapy (PT) is an increasingly available method to reduce off-target irradiation in CNS tumors due to the intrinsic properties of heavy-particle irradiation. Here, we review currently available data examining the used of PT in glioma patients, including dose escalation for GBM, re-irradiation (reRT) of recurrent glioma, and the potential cognitive sparing effects of conventional dose PT. We discuss the incorporation of PT into the multimodal therapy of GBM patients, and how the aggressive nature of the disease poses a unique challenge to PT study design. We also describe how PT may provide the most feasible method for implementing high rate 'FLASH' RT and the implications for glioma patients. We conclude with a discussion of ongoing clinical trials, the necessity of continued research, and how we interpret and incorporate available data into our current practice.