LEUKAEMIA INDUCED n\ RADIATION 



animals surh particles could nevertheless be demonstrated and in certain instances 

 of non-inalitinant tumours, no ]>arliclcs ran be demonstrated — rather relates to a 

 point whicii you made. Irradiation can bring fortii a burst of wiiat Berniiardt calls 

 'virus-like particles'. 



Dr. Loutit: Thank you. I should like to keep quite an open mind about viruses and 

 their relationship to tumours, but I would not. with no experience of viruses, exclude 

 that viruses are universally present in animal tissue and that normally they are kept 

 under control by the normal immunological mechanisms of the body. As I say by 

 either utilizing the newborn animal and adding so much extra-virus in a short burst 

 that the system is flooded, or by playing around with substantial doses of radiation 

 which certainly inactivate, />ra tetn., at any rate, the immunological mechanism, you 

 could bring about the spread of the virus, the consequent changes initiating a process, 

 or being one of the factors in a process, which ultimately results in leukaemia. More- 

 over, I think leukaemia and most malignant diseases, are mediated by several different 

 factors and these temporary disturbances of the post-virus relationship might well 

 be one of the intermediary factors. 



Dr. Sheldon: You gave the case of the American radiologists as being in the class 

 which received a high dose rate. I should expect it would be rather a small dose rate 

 over a long period like that in one of the other experimental classes mentioned later. 

 Dr. Loutit: I am not a radiologist, but there must be a number in the audience here. 

 I would guess that most radiologists get their exposure from screening operations 

 with a patient between them and the X-rays. During the time of exposure, it may 

 be only a few minutes, they are exposed to radiation at a high dose rate. There may 

 be an interval of a few minutes, a few hours, perhaps a few days, before they do 

 another series of screenings, but during the time of exposure the tube is activated and 

 they are exposed to the high rate. Would a radiologist confirm ? 



Dr. Deans: The figures concerning deaths from leukaemia amongst radiologists 

 referred to by Dr. Loutit were compiled from obituary notices by March, Ulrich 

 and others. These figures refer to an earlier generation of radiologists including 

 pioneers of radiology, many of whom were probably exposed to what could be called 

 a heavy dose of radiation at a high rate. As Martin and others have pointed out the 

 output of fluoroscopic installations in use even to the present day may, in exceptional 

 instances, be as high as 100 r per minute. 



Dr. Loutit: It seems likely that the protective measures which have been applied 

 in the last 30 to 40 years have altered the situation. Kaplan states that he knows of 

 absolutely no evidence that exposure to maximal permissible dose over a working 

 lifetime of some 40 years can induce leukaemia. A recent analysis of average age 

 at death from a variety of causes of radiologists, as compared with physicians not 

 exposed to radiation, has been made by Shields Warren. Lewis applied an age cor- 

 rection to Warren's data and came to the conclusion that radiologists in fact live 

 slightly longer than physicians in general. 



Sir MacFarlane Burnet: May I make one minor protest against the idea that all 

 mammals are all the time saturated with a large number of unrecognizable viruses? 

 I just cannot believe that. With regard to virus and cancer, I think one point that 

 was implicit in Dr. Loutit's discussion was that if somatic mutation or sequential 

 somatic mutation is concerned in leukaemia, then the emergence of leukaemia into 

 the overt disease may well require additional physiological or other factors. There 

 exists, I think, the possibility that rather casual viruses, with the appropriate material, 

 might push and act as a promoting factor, essentially to push the disease into overt 

 manifestation. But I have a very deeply ingrained suspicion of electro-microscopic 

 appearances which are not verified by the appropriate transfer, and I think it is a 

 dangerous concept to feel that you can at will postulate any unrecognizable virus in 

 the tissues that is required to support the hypothesis. 



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