LOCAL IRRADL\TION OF CXS WITH HIGH ENERGY PROTONS 349 





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Fig. 2. The sharp demarcation of the irradiated zone in the gray matter of the 

 spinal cord is seen to the right. Bordering the irradiated zone is a band of nuclear 

 fragments and adjacent to them numerous astrocytes with' swollen cytoplasm and a 

 few macrophages; further away rather well preserved nerve cells are observed. Proton 

 beam 1.5 mm broad. Dose: 20 krad. Thionin. X 150. The photographs are pub- 

 lished by courtesy of Acta Rddiologica. 



agcTi-eoations of erythrocytes. The ner\e cells, axons, myelin sheaths, and glial 

 cells appeared to be intact. After 3 days the uray matter within a zone about 

 10 mm wide showed exudation of plasma as well as multiple, and sometimes 

 rather large, hemorrhages. The nerve cells were degenerating. The white 

 matter was relatively spared and showed only slight perivascular disintegra- 

 tion of the nervous tissue. Slight inflammatory cellular proliferation was noted 

 in the meninges and cord corresponding to the irradiated region. At 4 to 6 

 days after irradiation, widespread deueneration and necrosis of the white 

 matter and abimdant hemorrhages in the gray columns were seen ; Fig. 3). 

 The approximate relationship between dose and time of appearance of 

 sisns was studied in a series ot animals irradiated with 5 to 40 krad. Animals 

 irradiated with 12 krad or less did not, over a year, show any clinical signs 

 or histologic changes in the cord. After a dose of 40 krad. paralysis of the 

 hind legs developed in 2 days. The histologic picture 5 days after irradiation 

 re\ealed necrosis considerably more extensi\e than that seen after a dose of 

 20 krad. In addition, numerous small hemorrhages appeared. 



