[Radiosurgery: basic principles].

Radiosurgery is a way of treating in-brain lesions which uses convergence of very thin multiple ionisation beams in a unique focus point coinciding with the target. This enables obtaining a therapeutic effect without opening the skull, and thus avoiding eventual complications or contraindications of classical neurosurgery. In certain cases irradiation can be delivered with submillimetric precision. This particularly new approach is historically essentially based on the work of the Swedish neurosurgeon Lars Leksell in the 50s. Since that time new imaging techniques (e.g. digital imaging) have considerably widened indications. Three ionisation beam sources are generally used in this context: gamma rays emitted by radioactive cobalt 60 sources for the Gamma Knife, high energy LINAC X-rays modified in comparison to their classical use in external radiation therapy, and, more rarely, protons produced in cyclotrons. Several teams world-wide are still perfecting and refining this developing technique.