CONCEPT AND CRITERIA OF RADIOLOGIC AGEING 



201 



advanced temporally, and the parenchyma, although not appreciably 

 damaged histopathologically in earlier phases, may show precocious loss of 

 parenchyma in the later phase of age-involution secondary to these changes. 

 With increasing doses in localized exposures the temporal advancement of 

 these processes is progressively greater. 



150 



170 190 200''^ 300 400 500 600 700 800 900 



Age (days) 



J L 



_L 



J_ 



20 40 



150 250 350 450 550 650 750 



Days after dose 



Normal ageing 



Phase I Phase II 



— -Phase m— 



-Phase IV— 



Predominance of 

 destructive tissue cfiange 



Predominance of 



regeneration 



and repair. 



Arteriole capillary 



fibrosis becomes more 



advanced than in controls 



Normally or maximally 



recovered parenchymal 



cellularity. Length of phase 



depends inversely on dose size 



Arteriole capillary fibrosis 



progressing and advanced 



Parenchyrr.al ageing. 

 Arteriolo capillary 

 fibrosis progressing. 

 Earliness of onset 

 and rate depend 

 directly on dose size 



Fig. 4. 



Localized ageing changes of this kind have been produced in many of the 

 organs of the body by external sources of radiation (NAS-NRC, 1961), in 

 radio-therapy patients and experimental animals, and by internally-deposited 

 radioactive isotopes (Casarett, 1952, 1956). The tissue changes involved in the 

 development of radiation-induced, or temporally advanced, nejjhrosclerosis 

 following localized, or generalized, irradiation from external sources (NAS- 

 NRC, 1961; Furth et al., 1959), or internal administration of ^wpo (Casarett, 

 1952, 1956) are histopathologically of the ageing type, since the fundamental 

 histopathological process in ageing of the kidney is essentially a nephro- 

 sclerotic process. 



