Proton therapy for vestibular schwannomas.

This chapter discusses the treatment of vestibular schwannoma using proton beam therapy (PBT), which has been used in stereotactic radiosurgery, hypofractionated stereotactic radiotherapy, and fully fractionated radiotherapy. Using PBT, almost no dose is delivered beyond the proton Bragg peak, so compared to photon therapy the integral dose is reduced and less dose may be delivered to specific normal tissues, which may, in turn, reduce some acute and/or late toxicities. In PBT, however, there are additional uncertainties, including range uncertainty, which requires a larger "safety margin" than is typically required for photon radiosurgery or hypofractionated stereotactic radiotherapy. The few published PBT series that describe patient outcomes are presented, all retrospective single center series, which do not suggest that local control or cranial nerve toxicity is more favorable than with photon therapy. Other toxicities, such as neurocognitive outcomes, risk of stroke, and radiation-induced malignancies, cannot be evaluated from the limited data. However, these series largely reflect now outdated treatment planning and delivery methods and do not include the latest Pencil Beam Scanning technology. It remains to be established whether outcomes with modern state-of-the-art PBT may be more favorable and whether particular subgroups, such as pediatric and young adult patients, may benefit.