THE MODIFICATION OF THE LATE EFFECTS OF 

 IONIZING KADIATION 



0. C. A. SCOTT 



Radiohiology Department, Mount Vernon Hospital and the Radium Institute, 



Northwood, Middlesex, England 



The literature on tlie delayed somatic effects of radiation has recently been 

 reviewed by Odell et nl. (1960). 



The difficulties encountered in this field have already been emphasized at 

 this meeting. There have been differences of opinion as to the very nature of 

 the ageing process. Can we study "protection" if we do not know what we are 

 protecting against? 



There are many difficulties in the planning of these experiments. For 

 instance, it is a fairly generally accepted principle that a dose-response curve 

 should be established, for a given biological system, before complicating 

 factors such as protective agents are introduced. In the case of one long-term 

 effect, carcinogenesis, every type of dose-resjjonse curve has been described. 

 Increasing the dose of radiation may give a steady increase in tumour yield, 

 an increase followed by a plateau, a steady reduction, or an increase followed 

 by a reduction (Furth et at., 1959; Hollcroft et al., 1957). It may be difficult to 

 elucidate the nature of the interaction of a protective agent with such com- 

 plex systems. Even when there is an apjDarently simple relationship between 

 dose and response, carcmogenesis experiments present planning difficulties. 

 For instance, Andervont (1943-4) showed that spontaneous tumour incidence 

 is dependent on the number of animals in a cage, and this number may fall 

 off in an experiment with total-body irradiation. Experiments using split 

 doses may also be difficult to interpret, if the incidence of the observed effect 

 varies with the age of the animal. 



If the criterion of radiation effect is shortening of life-span, the dose- 

 response relationship may be fairly simple, but interpretation is still compli- 

 cated by one's ignorance of the target-organ concerned. As Dr. Upton has 

 pointed out, we do not know whether cells, or non-ceUular elements, are 

 primarily involved. Professor Brinkman and Dr. Lamberts have shown 

 extremely interesting immediate effects of radiation on non-cellular elements, 

 but perhaps one should keep in mind the fact that aU non-ceUular elements 

 have been produced initially by a cell. Long-term effects on collagen may, 

 therefore, be secondary to ceU death. Odell et al. (1960) have reviewed the 

 rather scanty data on the specific problem of chemical protection against 



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