346 ANDERSSON, LARSSON, LEKSELL, MAIR, REXED AND SOURANDER 



and sweeping coils an almost parallel beam with a uniform cross section of 

 variable size was obtained. The desired beam profile was determined by a 

 final aperture. The mean dose-rate was 1,000-2,000 rad per min. The doses 

 were measured with an ionization chamber and by activation dosimetry. The 

 results obtained by the two methods were in fair agreement. Single proton 

 beams were used for irradiation of the rabbit's spinal cord and brain. Cross 

 fire irradiation was applied in the experiments on goats. 



In 55 rabbits and 5 goats, 3 types of lesions were produced : transection of 

 the spinal cord, transverse lesion of the cerebral hemispheres, and restricted 

 lesion in the depth of the brain. 



The spinal cord provides a suitable region to evaluate the effect of radia- 

 tion on nervous tissues because of its regular arrangement of gray and white 

 matter, and because disturbances of function are easy to observe. Proton 

 beams, 1.5, and 10 mm broad, were directed across the spinal cord under 

 deep intravenous nembutal anesthesia. The position of the animal was 

 checked by roentgenograms before and after irradiation. After irradiation 

 the animals were examined regularly, and neurologic symptoms noted. In 

 most cases, paresis of varying degree developed. The animals were sacrificed 

 by exsanguination under chloroform anesthesia at different periods following 

 appearance of paresis. 



In a second series of experiments performed in rabbits, the 1 .5 mm proton 

 beam was directed across the upper anterior part of the brain. A dose of 20 

 krad was used, llie skull was fixed to a frame to avoid movement. During 

 irradiation the animals were observed on a television screen. The animals 

 were allowed to survive from 2 to 56 weeks. During this time no functional 

 disability occurred which could be ascribed to the lesion. 



In view of the possible application of irradiation with high energy pro- 

 tons to neurosurgery, experiments on goats were performed. The goat has a 

 rigid skull which can be conveniently fixed in the same stereotaxic apparatus 

 as that constructed for man. The goat's brain is rather large, so that the 

 volume of necrotized tissue can be made relatively small compared to the 

 size of the whole brain. This fact reduces the risk of side efTects, e.g., general- 

 ized edema of the brain. One goat was irradiated with a single beam of pro- 

 tons (dose = 20 krad). In 3 goats a disc-shaped lesion with a diameter of 

 about 1 cm was produced in the internal capsule by the stereotaxic method 

 using cross fire irradiation. A beam 2 mm x 7 mm or 2 mm x 10 mm and 

 20-22 fields were used (the dose at the desired site was in 2 cases 20 krad 

 and in 1 case 38 krad ) . The head of the goat was fixed to the stereotaxic in- 

 strument by drills as described by Leksell (1951, 1957). When cross fire ir- 

 radiation was applied, a point in the right internal capsule was selected as 

 center of rotation. The lesions were planned so as to appear transverse to the 

 direction of the fibers of the internal capsule. Before the operation, the goats 



