Fractionated stereotactic radiotherapy for the treatment of optic nerve sheath meningiomas

Abstract

Radiosurgery has become an important treatment alternative to surgery for a variety of intracranial lesions. As currently practiced, it has in fact replaced surgery as a standard of care in some instances, compliments surgery as a post-operative adjunct in others, and most commonly represents an alternative to surgery or the only treatment option. Radiosurgery techniques have evolved quickly with the development of new technologies enabling more complex yet more efficient treatment plans. As a consequence, these technologies have broadened radiosurgery applications and improved radiosurgery outcomes. Among these newer techniques, treatments involving fractionated stereotactic radiation referred to as fractionated stereotactic radiotherapy, or FSR, have emerged as a consequence of linear accelerators designed for and dedicated to stereotactic techniques. Without the logistical constraints of retrofitted general purpose linear accelerators used in radiation oncology, often available only once or twice a week, dedicated units have enabled the design of treatment paradigms that strive for an ideal treatment based on the radiobiology of the target and dose-limiting contiguous tissues.This chapter will summarize our fifteen year experience with the Varian 600SR, initially with the Radionics software more recently modified to a Novalis shaped beam radiosurgery unit, and our practice of FSR for a variety of intracranial lesions. Special attention will be devoted to tumors involving or near the special sensory cranial nerves. Given the versatility of the Novalis treatment planning platform, one has the option of comparing different treatment planning solutions at once, including stereotactic intensity-modulated radiation therapy (IMRT). For selected skull base lesions, we have found that stereotactic IMRT yields greater conformality than FSR and we will therefore include its application among fractionation strategies.