in the operation theatre. He performed a large number of pallidotomies, and later also thalamotomies, in Parkinson's disease and capsulotomies in various forms of mental disorders. The results of a series of 81 patients subjected to pallidotomy was published in 1960, and 116 patients treated with capsulotomy were reported in 1961. Radiosurgery The term and concept of radiosurgery were introduced by Leksell already in 1951 when he reasoned that the ‘‘center-of-arc’’ principle and his first stereotactic instrument were suitable for replacing a probe (needle electrode) by cross-firing intracerebral structures with narrow beams of radiant energy. X-rays were first tried but both gamma rays and ultrasonics were included as alternatives. Initial experiments were performed on cats and then a few patients with pain and chronic psychosis were treated with a 280 kV X-ray tube attached to the arc. Of particular interest is that in 1953 two cases of trigeminal neuralgia were treated and at follow up in 1971 they were still free of pain. In 1946 Leksell was appointed head of a neurosurgical unit in Lund in southern Sweden where he became professor in 1958 and remained so until 1960. In those days there were very few neurosurgeons around the world who were active in stereotactic surgery and the international network was very small; it is of interest that the Schalten brand and Bailey's Stereotactic Atlas was partly based on some brain specimens supplied by Leksell. While in Lund, Leksell was apparently able to evade many of his clinical obligations because he was able to initiate a close collaboration with a team of physicists led by Börje Larsson at the University of Uppsala (north of Stockholm) where a synchrocyclotron was available. They conducted experiments with stereotactic high-energy proton irradiation in goats resulting in a seminal publication in Nature in 1958. This technique was also applied in a few patients with Parkinson's disease (pallidotomy), psychiatric disorder (capsulotomy) and pain (mesencephalotomy). Although precisely placed and well-limited lesions could be produced by the focused proton beams, as demonstrated in a few autopsy cases, the synchrocyclotron proved to be too complicated for general clinical use. This compelled Leksell to consider other radiation sources and he started designing the cobalt-60 gamma unit, which was fully integrated with the stereotactic system. The development of the ‘‘beam-knife’’ took place after Leksell had been appointed successor to Olivecrona in 1960 and the first unit was inaugurated in 1967. Later