gms | German Medical Science

Objective: Stereotactic radiosurgery of acoustic neuromas (ACN) is supposed to present a non-invasive treatment alternative to microsurgical resection with a low risk profile. However, longterm tumor control and the risk of decrease in auditory function or new-onset facial paresis still need to be evaluated. We here present the clinical and radiographic outcome in a large series of ACN treated with Cyberknife stereotactic radiosurgery.

Methods: We retrospectively analyzed 232 patients treated for ACN of all KOOS grades with single-fraction CyberKnife stereotactic radiosurgery in a single institution between 2011 and 2018. All patients underwent multislice computed tomography and 3D contrast enhanced and CISS MR imaging, followed by treatment planning using the Accuray software Clinical as well as treatment associated parameters were collected together with radiographic follow up.

Results: Median age of the population was 61.9 yrs (range 18.7 – 93.9 yrs). Median follow-up was 45.8months (range 12.3 – 88.7 months). The population included 44 Koos grade T1 (18.9%), 95 T2 (40.9%), 82 T3 (35.3) and 11 T4 (4.7%) tumors. Single-fraction doses between 12.5 and 13.5 Gy (median 13 Gy) were applied to the 70% isodose line. Median GTV irradiated was 0.58 (range 0.03 – 6.77) cm³. Mean dose applied was 15.7 Gy (range 14.05- 16.75 Gy). Median conformality was 1.2 (range 1.06 – 3.56).Auditory function was impaired pre-interventional in 203 cases (87.5%). Post-CK, hearing improved in 6 cases (2.6%), remained stable in 208 cases (89.6%) and decreased slightly in 18 patients (7.8%). No case of complete loss of auditory function was seen in patients with residual hearing pre-interventionally. 20 patients (8.6%) presented with facial paresis (FP) prior to radiation therapy. New-onset-FP was seen in an additional 7 patients (3.0%), with only 2 cases of severe FP (0.1%), requiring surgical intervention. Tumor control was achieved in 219 cases (94.4%) with substantial or partial response in 32 (13.7%) and 107 (46.1%) patients respectively and stable disease (no change) in 79 patients (34.0%). Adverse effects remained rare. Symptoms of trigeminal neuralgia occurred in 5 cases (2.2%). Focal edema was seen in 13 cases (5.6%), with only three cases (1.3%) requiring steroid treatment.

Conclusion: In our large cohort of ACN of all KOOS grades, CyberKnife radiosurgery provides satisfying tumor control and preserves hearing function with low rates of new-onset FP or other adverse effects.