Proton Radiosurgery: Current Concepts and Limitations for CNS Radiosurgery

Stereotactic radiosurgery (SRS) is highly conformal, high-dose radiation therapy delivered in 1-5 fractions, and is considered the standard of care for several central nervous system (CNS) indications. Particle therapies, such as protons, have physical and dosimetric advantageous properties compared to photons. However, proton SRS (PSRS) is not widely performed given the few particle therapy facilities, high-cost, and limited outcomes research as a sole modality and in comparative studies. The data available differs from each pathology. For AVMs, especially those with deep or eloquent locations, PSRS obliteration rates outcomes appear favorable and superior. For meningiomas, PSRS has been used for grade 1 alone, and for higher grades a PSRS boost has been considered. For vestibular schwannoma, PSRS seems to have favorable control rates with modest toxicity outcomes. For pituitary tumors, data shows excellent results with PSRS for functional and non-functioning adenomas. For brain metastasis, moderate doses of PSRS achieves high local control rates with low rates of radiation necrosis. For uveal melanoma, dedicated eyeline PSRS (4-5 fractions) are associated with very high tumor control and eye retention rates.

PSRS is effective and safe for various intracranial pathologies. Limited data, usually retrospective and single institution series exist. There are numerous advantages of protons over photons, so it is important to understand limitations with further studies. Published clinical outcomes and widespread adoption of proton therapy will be key to unlocking the potential benefits of PSRS.