MORPHOLOGICAL EFFECT OF X-RAYS TO THE CNS 



217 



positioned on the mid-dorsal skull. Technical conditions included: 40 kv, 

 25 ma, filter 0.3 mm Al, and focus-skin distance 5.5 cm. To determine more 

 exactly the actual intracerebral radiation, the x-ray dosage was measured by 

 a Siemens dosimeter at a level to include skin, bone, and 1 mm of brain 

 substance, which means that within a distance of 2.5 mm about 50% of 

 the surface dose was measured. Further \alues were obtained by using 1 mm 

 plates of a phantom material, Cellon, which has the same absorption value 

 as brain tissue. This procedure indicated a diminution of the dose in dif- 

 ferent regions (Fig. 7). EflFective x-radiation values of 1,000 to 80,000 r 

 were administered to the cerebral cortex with application times of 28 sec to 

 37 min 34 sec, respectively. Doses of 20,000 r and more were badly tolerated 

 by the animals; generally they died spontaneously 2 or 3 days later. Young 

 animals seemed to be more sensiti\e than older ones, and on the average 

 showed more sexere morphologic changes. With the application of 30,000 r, 

 sharply limited zones of total necroses, sometimes containing numerous small 

 hemorrhages, could be produced and were fully de\eIoped after 67 to 68 



Cellon 

 mm 



10 



10 20 30 40 50 

 (mm) 



Fig. 7. Equi\alent doses for special tube used with soft x-ray radiation. The diagram 

 demonstrates the diminution of the x-ray dose at different levels in the tissue. The 

 figures represent the effecti\e dose in percentages of the surface dose. The abscissa 

 demonstrates the diffusion of the x-ray beam within the tissue. 



