J Neurol Surg A Cent Eur Neurosurg 2014; 75 - p77
DOI: 10.1055/s-0034-1383804

Tailored Radiosurgical Planning in Vestibular Schwannomas in the Era of Gamma Knife Perfexion: A Prospective Series of 183 Consecutive Cases

C. Tuleasca 1, 2, 3, 4, M. George 4, 5, L. Schiappacasse 4, 6, M. Zeverino 7, R. Maire 4, 5, R.-T. Daniel 1, 4, M. Levivier 1, 4
  • 1Centre Hospitalier Universitaire Vaudois (CHUV), Neurosurgery Service and Gamma Knife Center, Lausanne, Switzerland
  • 2Swiss Federal Institute of Technology (EPFL), Laboratory of Transmission Signal (LTS-5), Lausanne, Switzerland
  • 3Centre Hospitalier Universitaire Vaudois (CHUV), Medical Image Analysis Laboratory (MIAL), Lausanne, Switzerland
  • 4University of Lausanne, Faculty of Biology and Medicine, Lausanne, Switzerland
  • 5Centre Hospitalier Universitaire Vaudois (CHUV), Department of ENT, Head & Neck Surgery, Lausanne, Switzerland
  • 6Centre Hospitalier Universitaire Vaudois (CHUV), Radiation Oncology Service, Lausanne, Switzerland
  • 7Centre Hospitalier Universitaire Vaudois (CHUV), Institute of Radiation Physics, Lausanne, Switzerland

Aims: Gamma Knife surgery (GKS) with Leksell Gamma Knife Perfexion® (LGK-PFX, Elekta Instruments, AB, Sweden) started in CHUV in July 2010. We present our series of vestibular schwannomas (VS), with emphasis on those treated with GKS as a first intention, focusing on planning parameters to optimize functional outcome.

Methods: We prospectively analyzed 183 cases over a period of 3.7 years. Patient’s characteristics, as well as anatomical, clinical and dose planning parameters were collected in a dedicated case-report form. During planning, special attention was given to the dose to the cochlea, in relation with its impact in maintaining a serviceable hearing.

Results: We excluded 17 patients with combined approaches (planned subtotal resection followed by GKS on the residual tumor), 3 patients operated elsewhere with residual tumors, 6 cases treated elsewhere and presenting with recurrences, 3 cases with intracochlear extension and 2 cases of neurofibromatosis. A total of 149 VS was finally analyzed, of whom 88 (59%) had serviceable hearing (39.6% with Gardner-Robertson (GR) class 1 and 19.4% with GR 2) before GKS. The mean follow-up period was 1.1 years (0.3- 3.5). The mean maximal diameter was 15.6 mm (4-29.5). The size and volume of the tumor corresponded to Koos grade I, II, III and IV in 15.9%, 34.8%, 45.4% and 3.8% of the cases, respectively. The mean target volume was 1.24 cc (0.017-7.8). The mean prescription isodose volume was 1.6 cc (0.032-8.5). The mean marginal dose was 12 Gy (11-12). The mean maximal dose received by the cochlea in patients with GR class 1 and 2 was 4.1 Gy (1.5-7.6). Our preliminary neuroradiological follow-up shows 97% tumor control, with 45% shrinkage. Patients presenting with GR class 1 and class 2 at baseline retained serviceable hearing in 85% of cases.

Conclusions: LGK-PFX represents a clear technical advance in radiosurgery for the treatment of VS. The advantages consist especially in the possibilities of shaping of the isodoses in very complex manners, allowing high conformity and selectivity, and sharp selective gradient to deliver a very low dose to the cochlea (<=4 Gy, whenever possible), even when the distance to the intracanalicular part of the tumor is of few millimeters. Further long-term follow-up is needed to confirm the high-quality of the functional results.