Mature treatment results of 120 cases of acoustic neuroma treated with cyberknife at a single institution

Background Stereotactic radiosurgery (SRS) is a noninvasive alternative to microsurgery in the management of acoustic neuromas. Single fraction Gamma Knife SRS of acoustic neuromas results in high rates of local control (85-97 %). CyberKnife (CK) Robotic SRS is an alternative technique delivering the same quality SRS but with the benefits of a frameless treatment system allowing for fractionated treatment. The body of evidence in its use for acoustic neuromas is less robust. We present mature outcomes of a large cohort of patients treated with CK at a single institution. Methods This study consisted of 120 acoustic neuroma patients treated with CK from Sept 2010 until March 2016. Patients with complete hearing loss were treated with a single 12 Gy fraction (6 Pts). Those with hearing preservation or moderate to large tumors were treated with 18 Gy in 3 fractions (114pts). Follow-up T2 axial MRIs (0.50 mm slice) were analyzed to evaluate rates of tumor control and incidence of pseudo-progression. To obtain volumetric response data, MRI images were contoured on PACs imaging station using Aquarius Net version 4.4.13 by a single radiation oncologist. Results Patients range in age from 15 to 91 (mean 58). The median follow up time was 60 months. Mean tumor size was 2.8 cm3 (Range 0.1-30). Progression occurred in 4 patients (local control rate of 97%). Pseudo-progression was seen in 17 cases. For patients with pseudo-progression mean time to the maximum imaged tumor volume post treatment was 5 months (Range of 3 to 12 months) with an average volume increase of 11% (Max 31%). Mean time to subsequent regression to pre-treatment size was 15 months (Range of 10-23) No pseudo-progression led to subsequent local recurrence. There were low rates of late toxicity. One patient who progressed suffered CN VII palsy prior to salvage surgery. All other patients had preserved CNV and CNVII function and there was no case of brain stem necrosis. Conclusions Cyberknife offered high rates of durable local control (97 %) for acoustic neuromas with low rates of toxicity. Pseudo-progression was seen in 14% of patients and was not a predictor for treatment failure. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure S. Malone: Honoraria (self): Janssen; Honoraria (self): Astellas; Travel / Accommodation / Expenses: TerSera; Honoraria (self): AstraZeneca; Honoraria (self): AMGEN; Travel / Accommodation / Expenses: Sanofi; Honoraria (self): Abbvie; Honoraria (self): Bayer. All other authors have declared no conflicts of interest.