Radiosurgery versus Fractionated Stereotactic Radiotherapy for the Treatment of Vestibular Schwannoma

Introduction: To compare the treatment outcome and toxicity of fractionated stereotactic radiotherapy (SRT) with proton radiosurgery (SRS). Methods: Between 1992 and 2001, 171 patients with vestibular schwannoma were treated with SRT (n = 66) or SRS (n = 105) at our institutions. The median ages were 53 and 66 years in the SRT and SRS groups, respectively. The median tumor volume was 1.6 cc (SRT, 2.4 cc; SRS, 1.5 cc; p = 0.0007). Twenty percent in the SRT group and 15% of the SRS group had undergone surgical resection prior to radiation. The median dose in the SRT group was 54 Gy in 1.8 Gy per fraction, whereas the median dose in the SRS group was 12 Gy prescribed to a median 90% isodose line. The median follow-up durations of patients were 69 and 75 months in the SRT and SRS groups, respectively. Results: The actuarial local control rates at 5 years were 96% and 97% for the SRT and SRS group, respectively (p = 0.79). The actuarial rates of freedom from surgical resection or re-irradiation at 5 years were 93% and 97% for the SRT and SRS groups, respectively (p = 0.32). For toxicity analysis, patients were stratified into subgroups based on previously identified risk factors: tumor volume 1.6 cc, surgery before radiation, and maximum dose (Dmax). Dmax of 17.1 Gy and not Dmax < 13.3 in SRS group was predictive for lower rate of facial nerve preservation in all subgroups in the SRS compared with SRT. For SRS patients who had not undergone surgery before radiation and with tumor volume 1.6 cc were at higher risk of developing trigeminal neuropathy despite Dmax was limited to 13.3 Gy (97% in SRT vs 71% in SRS group). Conclusions: The local control rates are similar between the SRT and SRS groups. When Dmax is limited to 13 to 17 Gy, the risk of facial neuropathy is similar in both groups. Fractionation is important in the preservation of trigeminal nerve function.