XIII 



THE BIOLOGICAL EFFECTIVENESS OF X-RAY 

 WAVE-LENGTHS 



Charles Packard 



Institute of Cancer Research, Columbia University, New York 



The radiations whose biological effects are discussed in this paper 

 consist chiefly of roentgen rays generated at various voltages from 10 kv. 

 to upward of 500 kv. The range of wave-lengths involved is thus very 

 great, extending over more than five octaves, from 2.0 A to less than 

 0.05 A. The reactions which they produce can be compared with those 

 elicited by the alpha, beta, and gamma rays of radium, but since the 

 intensities of the latter radiations have not been successfully measured 

 in roentgens, such comparisons must be made with caution. 



The biological effects produced by these various qualities of radiation 

 can be considered from two points of view, the qualitative and the quanti- 

 tative. Do they vary in nature depending on the wave-length of the 

 incident beam, and do they vary in magnitude when equal amounts of 

 radiation of different wave-lengths are given? The answers to these 

 questions have been sought from the time that X-rays and radium first 

 began to be used in therapy, and yet today there is no unanimous opinion 

 on either of them. 



QUALITATIVE EFFECTS 



The first radiologists believed that X-rays of different qualities were 

 capable of producing different kinds of reactions in tissues. This was a 

 natural inference, for it was known that in the region of visible light and 

 the ultra-violet, specific wave-lengths produced specific effects. And 

 experience showed that soft X-rays, filtered very lightly or not at all, 

 produced severe but superficial burns in the skin while hard, highly 

 filtered rays did not, because, as was supposed, the caustic rays had been 

 removed. For a tim« the hard rays were believed to have healing proper- 

 ties. But in 1915 Rost (35) pointed out that both hard and soft rays 

 cause the same histological changes in the skin and other tissues. Later 

 work has confirmed his conclusions. Thus Reisner (34) remarks that 

 "the erythema reaction of the human skin after exposure to gamma rays, 

 that is, to the hardest radiation, does not differ fundamentally from that 

 produced by hard, soft, or very soft X-rays." Differences in the magni- 

 tude of the reaction are due, as Rost showed, to the relative amount of 



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