LOCAL IRRADL\TIO\ OF CNS WITH HIGH ENERGY PROTONS 357 



est beam used was 1.5 mm broad, and lesions produced by this beam were 

 not studied before 9 days after irradiation. When the 10 mm-broad beam 

 was used and the histolooy of the spinal cord studied 1 to 6 days after 

 irradiation, vascular changes were found at the time when only slisjht 

 destruction oi myelin sheaths had appeared. This obser\ation stresses the 

 possible importance of \ascular changes amon^" the causal factors of delayed 

 radionecrosis in the nervous system. Furthermore, the presence of a thin 

 peripheral zone ol the cord with undamaoed ner\e fibers may speak in 

 favor of vascular factors, since it is well known that the peripheral region 

 of the cord is relati\ely resistant to impaired circulation. The studies of 

 Larsson 1960) on blood \essel chanscs following local irradiation of the 

 rat's brain with high energy protons indicate that disturbances in capillary 

 circulation may precede increased permeability of the blood-brain barrier 

 system for trypan blue. The latter type of changes was accompanied or 

 succeeded by destruction of nervous tissue. 



In the rabbit's brain irradiated with high energy protons, capillary pro- 

 liferation and sometimes teleangiectasis appeared within the lesion. It might 

 be supposed that such changes of vessels would predipose to hemorrhage, 

 but in fact a large hemorrhage was never seen either in the late or early 

 stages after irradiation. Teleangiectasis was also obser\"cd by Berg and 

 Lindgren i 1958 I in the rabbit's brain after roentgen irradiation. 



The various types of giant cells found at the margins of the radiolesion in 

 rabbit's brain were probably of glial origin and resembled the cells foimd 

 in gliomata. These cells were always confined to the margins of the lesion 

 and were ne\er found to have spread to other parts of the brain. The 

 ninnber of the giant cells did not increase during the experiment of one 

 year. Exceptionally large astrocytes were described in rabbits after roentgen 

 irradiation of the brain by Russell ct al. : 1949 ) . and giant, atypical glial cells 

 ha\c been obserxed in primates by Arnold and Bailey 1954 i and Berg and 

 Lindgren il958). 



The experiments reported show that, with a narrow beam of high energy 

 protons, sharply delimited acute lesions at a desired site in any region in the 

 central nervous system can be produced. Furthermore, it is obvious that by 

 careful selection of doses and dose distributions, well circumscribed intra- 

 cerebral lesions of appropriate size and shape can be caused. However, this 

 statement is valid only for the earlier stages of the radiolesion, as only 

 relatively short survi\al periods are considered. To what extent high energy 

 protons may be used in stereotaxic surgery of the hiunan brain depends on 

 the late changes. The long-term effects of high energy proton irradiation 

 are at present being studied in a series of experiments on goats, in which 

 deep lesions are to be followed up over several years. 



