Proton beam therapy for intracranial and skull base tumors

Radiotherapy is widely used for treating malignant and benign intracranial or skull base tumors because of the difficulty in performing wide or complete tumor resection due to the involvement of eloquent areas, vital vessels, or cranial nerves. Similarly, local radiotherapy with conventional methods may sometimes be inefficient for treating brain tumors because the tolerance doses for the optic nerves, eyes, and brainstem are strictly limited. Under the circumstances, particle radiotherapy with proton or carbon ion beams has excellent dose localization to the target volume owing to the sharp Bragg peak ionization in the human body. With this property, it is possible to deliver higher doses to tumors of various shapes while preserving the surrounding critical brain structures. Although the efficacy of proton beam therapy (PBT) has been suggested for skull base chordoma and unresectable meningioma, further clinical evidence is required for optimization and standardization of the therapy. In refractory tumors such as glioblastoma multiforme and anaplastic meningioma, it is necessary to deliver high doses to improve tumor control. Under these circumstances, protons or carbon ions have potential to deliver sufficient doses to the target while keeping the healthy brain intact. In this context, we focus on the current status of proton beam radiotherapy for treating intracranial and skull base tumors.