Introduction
Stereotactic radiosurgery (SRS) was invented by the Swedish neurosurgeon Lars Leksell in the early 1950’s1. The word “stereotactic”, frequently employed in “SRS”, refers to a three-dimensional coordinate system, which enables accurate correlation of a virtual target, seen in patient’s therapeutic images, with the actual target position in the patient’s head. In 1968, Leksell conceived the Gamma Knife (GK), a radiosurgical technique using multiple cobalt-60 radiation sources, initially as at tool for treating functional disorders. Gamma Knife radiosurgery (GKRS) is a neurosurgical stereotactic procedure, combining image guidance with high-precision convergence of multiple gamma rays, emitted by 192 sources of Cobalt-60, which is manufactured and commercialized in its latest fully robotized versions as Leksell Gamma Knife® (LGK) Perfexion™ and ICON™ (Elekta Instruments AB, Stockholm Sweden).
The mechanisms of action of SRS are not completely understood. They differ according to the treated pathology and the stereotactic targeting strategy. In the case of tumors, apoptosis may be the major mechanism of cell death; in vascular malformations, obliteration by thrombotic endothelial proliferation; in functional disorders, GKRS is used either to target a specific anatomical point in an anatomical structure (e.g. thalamus, anterior limb of the internal capsule, trigeminal nerve) or to target a larger zone, such as an epileptic focus, and the mechanism of action may differ.
Vestibular schwannomas (VS) are intracranial tumors derived from the myelinforming cells of the vestibulo-cochlear nerve. They are benign, extra-axial, tumors and account for around 80% of tumors located at the level of the cerebellopontine angle and 5-10% of all intracranial tumors. The prevalence in the general population is about 0.2-1.7 per 100.000 inhabitants. Therapeutic options are “wait-and-scan” strategy, microsurgery resection (usually reserved for large tumors), and SRS. Stereotactic radiosurgery of small to medium-size VS has a long-term clinical and scientific track record. There is a high rate of tumor control, as high as 97-98%. There was a refinement of the technique over time, with a progressive decrease in the prescribed radiation dose, leading to similar tumor control and further decrease of toxicity, in particular for the facial nerve function. Hearing preservation varies depending on series. Moreover, there is a need of long-term data with regards to this latter outcome.
Here, we focus on the evaluation of the 3-year follow-up outcome after SRS with GK for VS treated at the Lausanne University Hospital (CHUV), Switzerland. Pertinent clinical and radiological aspects are discussed. All patients have been treated with the latest versions of LGK, enabling us to present modern data with this approach.