Leksell and Larsson first employed proton beams coming from several directions into a small area into the brain,[2] in experiments in animals and in the first treatments of human patients.
In 1945 he presented a PhD dissertation, a monograph on the motor gamma system titled ‘‘The action potential and excitatory effects of the small ventral root fibers to skeletal muscle.’’[6] This was a major milestone in the understanding of muscle control and has now become part of basic neurophysiology.
During these years he, together with Granit and Skoglund, made another major contribution by describing the phenomenon of ephapsis, ‘‘artificial synapses,’’ caused by local pressure on a nerve, as a possible mechanism involved in trigeminal neuralgia.
The stereotactic method is the product of Robert Clarke, an engineer, physiologist and surgeon, who, together with neurosurgeon Victor Horsley, devised an instrument for simulating and making lesions at exact locations within the brains of experimental animals: the Horsley–Clarke apparatus.
Their original frame, using a Cartesian coordinate systems and similar in design and operation to the Clarke-Horsley device, was fixed to a patient's head by means of a plaster cast.
Contrast radiography, ventriculography and later pneumoencephalography permitted the visualization of intracranial reference points from which the location of target structures of interest could be determined.
Leksell was in many respects a perfectionist and for the rest of his life he continued to change and revise the design of virtually every small part of his instrument though the basic semicircular frame was retained.
An important feature was that ‘‘the apparatus should be easy to handle and practical in routine clinical work’’ and ‘‘a high degree of exactitude is necessary.’’ An oft-cited quotation is ‘‘Tools used by the surgeon must be adapted to the task and where the human brain is concerned, no tool can be too refined.’’[10] The first, documented clinical application of Leksell's stereotactic system was a case of a craniopharyngioma cyst that was punctured and treated with injection of radioactive phosphorus.
[13] 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.
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.
[15] 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.
[16] Originally, radiosurgery and the gamma unit were developed with the hope that it would offer a bloodless, and less risky, method to be applied principally in functional neurosurgery, for example in thalamotomy for Parkinson's disease.
On the other hand, Leksell had always considered his stereotactic instrument a surgical tool that should also be utilized in general neurosurgery in order to enhance precision and minimize hazards.
The gamma unit soon proved to be useful in the treatment of some diseases previously requiring neurosurgery, such as pituitary adenomas, acoustic neurinomas and arteriovenous malformations.