Hypofractionated radiosurgery (25 Gy/5 fractions) for optic nerve sheath meningiomas: results from an exploratory phase 2 prospective trial.

Background: Traditional treatment options for optic nerve sheath meningiomas (ONSMs) include observation, surgery, and radiotherapy; however, none of these has emerged as the definitive treatment of choice to date. Preliminary results on the application of hypofractionated radiosurgery have been quite promising in terms of preserving visual function and achieving local tumor control.

Objective: An exploratory trial was conducted to evaluate the safety and effectiveness of hypofractionated radiosurgery (25 Gy in 5 fractions) for ONSMs.

Methods: From May 2011 to May 2019, 50 patients with ONSMs were consecutively enrolled and treated with radiosurgery using the frameless CyberKnife system. Patients had median age of 49 years (19-78 years). All patients were treated using hypofractionated radiosurgery, receiving 5 fractions of 5 Gy each, for a total dose of 25 Gy, prescribed at the 75% to 85% isodose line. Patients were evaluated for visual function through visual acuity and visual fields examination, and for local control through volumetric measurement of the tumor.

Results: The median follow-up was 6 years (IQR 4.7-9.7 years). All patients tolerated the treatment well, with only 4 (8%) experiencing a reduction in visual acuity. No additional acute or late radiation-induced toxicities were observed. No retinopathy was described. No patients had worsening of visual field function. No patients showed ONSMs progression on MRI follow-up.

Conclusions: In this exploratory trial, hypofractionated radiosurgery (25Gy/5 fractions) for ONSMs appears safe and effective in terms of visual function and growth control, which may be validated in future multi-institutional study with longer term follow up.