LAMINAR LESIONS IN CEREBRAL CORTEX 367 



TABLE I 



Relation' of Peak Doses to Histological Fixdinos 



Number and type of lesions " 



Peak doses '' No evidence 



(in 1 ,000 rods) of lesion Light laminar Heavy laminar Necroti foci 



< 14 6 9 — — 



15-24 1 16 — — 



25-34 _ 20 10 2 



35-44 _ 8 25 16 



45-54 _ _ 7 29 



>55 -- — 4 24 



•' Findings for 177 radiation lesions in rabbits survi\ing from 2l! to J48 days. 

 '' Siiigle irradiations with 20 Mcv deuterons. 



The lesion is defined as litiht laminar if the destruction is restricted to the 

 zone of maximal ionization throughout the entire irradiated region. It is 

 called a heavy laminar lesion if the band of destruction is broader and some 

 changes are manifest for a short distance above the zone of maximal ioniza- 

 tion. A lesion is classified as showing a necrotic focus if anywhere within the 

 irradiated region there is a sign of vascular occlusion or its sequelae. Only 

 some lesions in the last category (produced by very large doses) display signs 

 of radiation necrosis throughout the entire irradiated region. 



The table implies that each type of lesion can be produced by a large 

 span of radiation doses, even if one assumes that some extreme figures in 

 each category merely represent an apparent spread due to errors in determi- 

 nation of the deli\ered doses. Several conclusions are apparent. A peak dose 

 of about 30,000 rads (which corresponds in our irradiation to a surface dose 

 of approximately 6,000 rads and an a\ erage dose of about 10,000 rads) leads 

 almost invariably to excellent laminar destruction. A peak dose up to 45,000 

 rads often produces hea\y laminar destruction; on the other hand, a peak 

 dose can be reduced to about 15,000 rads and still almost always result in 

 a narrow, light laminar lesion. Peak doses below 15,000 rads may fail to 

 produce lesions, at least for many weeks or months, while doses in excess of 

 45.000 rads can be expected to produce necrotic foci. 



It appears that a peak dose of about 15,000 rads can be tentatively 

 accepted as a reasonable approximation of a minimal dose, which must be 

 applied over a short distance in the cortex to produce total destruction of 

 nerve cells within a few weeks. It follows from this consideration that a 

 surface dose of about 15.000 rads (which roughly corresponds to a peak dose 

 of 75.000 rads) should be necessary to produce total necrosis of the irradi- 

 ated cortex with our beam. This expectation seems in reasonable agreement 



