title: Acute clinical adverse radiation effects after Gamma Knife surgery for vestibular schwannomas.
abstract: OBJECTIVE Vestibular schwannomas (VSs) represent a common indication of Gamma Knife surgery (GKS). While most studies focus on the long-term morbidity and adverse radiation effects (AREs), none describe the acute clinical AREs that might appear on a short-term basis. These types of events are investigated, and their incidence, type, and outcomes are reported in the present paper. METHODS The included patients were treated between July 2010 and March 2016, underwent at least 6 months of follow-up, and presented with a disabling symptom during the first 6 months after GKS that affected their quality of life. The timing of appearance, as well as the type of main symptom and outcome, were noted. The prescribed dose was 12 Gy at the margin. RESULTS Thirty-five (22%) of 159 patients who fulfilled the inclusion criteria had acute clinical AREs. The mean followup period was 30 months (range 6-49.2 months). The mean time of appearance was 37.9 days (median 31 days; range 3-110 days). In patients with de novo symptoms, the more frequent symptoms were vertigo (n = 4; 11.4%) and gait disturbance (n = 3; 8.6%). The exacerbation of a preexisting symptom was more frequently related to hearing loss (n = 10; 28.6%), followed by gait disturbance (n = 7; 20%) and vertigo (n = 3, 8.6%). In the univariate logistic regression analysis, the following factors were statistically significant: age (p = 0.002; odds ratio [OR] 0.96), hearing at baseline by Gardner-Robertson (GR) class (p = 0.006; OR 0.21), pure tone average at baseline (p = 0.006; OR 0.97), and Koos grade at baseline (with Koos Grade I used as a reference) (for Koos Grade II, OR 0.17 and p = 0.002; for Koos Grade III, OR 0.42 and p = 0.05). The following were not statistically significant but showed a tendency toward significance: the number of isocenters (p = 0.06; OR 0.94) and the maximal dose received by the cochlea (p = 0.07; OR 0.74). Fractional polynomial regression analysis showed a nonlinear relationship between the outcome and the radiation dose rate (minimum reached at a cutoff of 2.5 Gy/minute) and the maximal vestibular dose (maximum reached at a cutoff of 8 Gy), but the small sample size precludes a detailed analysis of the former. The clinical acute AREs disappeared in 32 (91.4%) patients during the first 6 months after appearance. Permanent and somewhat disabling morbidity was found in 3 cases (1.9% from the whole series): 1 each with complete hearing loss (GR Class I before and V after), hemifacial spasm (persistent but alleviated), and dysgeusia. CONCLUSIONS Acute effects after radiosurgery for VS are not rare. They concern predominantly de novo vertigo and gait disturbance and the exacerbation of preexistent hearing loss. In de novo vestibular symptoms, a vestibular dose of more than 8 Gy is thought to play a role. In most cases, none of these effects are permanent, and they will ultimately improve or disappear with steroid therapy. Permanent AREs remain very rare.
authors.affiliation: Department of Clinical Neurosciences, Neurosurgery Service and Gamma Knife Center.|Signal Processing Laboratory (LTS 5), Ecole Polytechnique Fédérale de Lausanne (EPFL).|Faculty of Biology and Medicine, University of Lausanne, Switzerland.
authors.forename: Constantin
authors.initials: C
authors.lastname: Tuleasca
authors.affiliation: Department of ENT Surgery.|Faculty of Biology and Medicine, University of Lausanne, Switzerland.
authors.forename: Mercy
authors.initials: M
authors.lastname: George
authors.affiliation: Institute of Social and Preventive Medicine, and.|Faculty of Biology and Medicine, University of Lausanne, Switzerland.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Faouzi
authors.affiliation: Radiation Oncology Service, Lausanne University Hospital (CHUV), Lausanne.|Faculty of Biology and Medicine, University of Lausanne, Switzerland.
authors.forename: Luis
authors.initials: L
authors.lastname: Schiappacasse
authors.affiliation: Department of Clinical Neurosciences, Neurosurgery Service and Gamma Knife Center.|Division of Neurosurgery, Centre Hospitalier Régional Universitaire de Lille, France; and.
authors.forename: Henri-Arthur
authors.initials: HA
authors.lastname: Leroy
authors.affiliation: Institute of Radiation Physics, Lausanne, Switzerland.
authors.forename: Michele
authors.initials: M
authors.lastname: Zeverino
authors.affiliation: Department of Clinical Neurosciences, Neurosurgery Service and Gamma Knife Center.|Faculty of Biology and Medicine, University of Lausanne, Switzerland.
authors.forename: Roy Thomas
authors.initials: RT
authors.lastname: Daniel
authors.affiliation: Department of ENT Surgery.|Faculty of Biology and Medicine, University of Lausanne, Switzerland.
authors.forename: Raphael
authors.initials: R
authors.lastname: Maire
authors.affiliation: Department of Clinical Neurosciences, Neurosurgery Service and Gamma Knife Center.|Faculty of Biology and Medicine, University of Lausanne, Switzerland.
authors.forename: Marc
authors.initials: M
authors.lastname: Levivier
mesh_terms: D000208:Acute Disease; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000532:radiotherapy*; D016634:Radiosurgery / Q000009:adverse effects*; D012189:Retrospective Studies; D013997:Time Factors; D055815:Young Adult
keywords: ARE = adverse radiation effect; CN = cranial nerve; GKS = Gamma Knife surgery; GR = Gardner-Robertson; Gamma Knife surgery; HB = House-Brackmann; OR = odds ratio; PIV = prescription isodose volume; PTA = pure tone average; RS = radiosurgery; TV = target volume; VS = vestibular schwannoma; adverse radiation effects; disturbance; gait; hearing; loss; radiosurgery; stereotactic radiosurgery; vestibular schwannoma