CONCEPT AND CEITERIA OF RADIOLOGIC AGEING 



G. W. CASARETT 



Sdiool of Medicine and Dentistry, The University of Rochester, New York, U.S.A. 



SUMMARY 



Critical general comparison of various manifestations of ageing and late radiation 

 effects strongly suggests premature againg as an effect of irradiation, on a generalized or 

 localized basis. Presented is an hypothesis of the process of "radiologic ageing" at the 

 tissue level, based on histopathological studies of the development of manifestations of 

 ageing and of late radiation effects in tissues prior to disease development. This hypothe- 

 sis maintams that non-specific injury of endothelium of fine vasculature by direct or 

 indirect mechanisms leads to increase in density and amount of collagenous substance 

 interstitially and in subendothelial regions of arterioles. These changes constitute a 

 temporal advancement in the increase of the histohaematic barrier and in the development 

 of arteriolocapillary fibrosis, which are progressive processes in "normal" ageing. 

 Eventually these processes cause progressive reduction in number of dependent paren- 

 chymal cells due to relative h\-poxia and malnutrition. Secondary to parenchymal loss 

 is a process of replacement fibrosis and reduction of fine vasculature, with consequent 

 further increase in histohaematic barrier and arteriolocapillary fibrosis. Concomitant 

 with parenchymal loss is progressive reduction of functional reserve capacities and a 

 corresponding progressive increase in susceptibHity of tissues to trauma, stress, and 

 disease. 



AMougli it is not yet possible to define and compare the essential processes 

 of ageing and of late radiation effects, their late manifestations can be 

 compared. 



The manifestations of ageing in adult mammals comprise a progressive 

 deterioration of tissues, with concomitant decline of functional reserves and 

 adaptive powers, which leads eventually to disease and inevitably to death. 



Ageing is not uniform with increasing time, but varies in rate among 

 individuals and among organs of an individual. The rate of ageing, the 

 development of disease, and the life-span are the net results of many variable, 

 modifying, conditioning and correlating forces, both environmental and 

 inherent, mcluding genetic constitution. The integration of these forces 

 determines the physical status of the ageing individual. 



There are four general types of data which are often used as criteria of 

 alteration of ageing process by irradiation. These are: data pertaining to 

 mortality, pathology and disease incidence, subclinical histopathology, and 

 physiology (mcluding biochemistry). It is fruitful to examine these criteria 

 critically in relation to one another, in a general manner, to determine their 

 relative usefulness with respect to assessment of the agemg process. 



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