PREFACE 



In this volume are published the papers and the discussion of the third joint 

 UNESCO and IAEA sponsored Symposia on topics of radiobiology related 

 to fundamental cell biology. 



The first of these symposia was held in Venice in June 1959, and the 

 second in Moscow in October 1960. Both concentrated on the nature of the 

 initial processes at the sub-cellular level which are responsible for initiating 

 the chain of events that leads to cell damage. In this, the third of these sym- 

 posia, it was decided to enter a less extensively studied area of radiobiolog}' 

 and one to which cell biology has not so far made a very large contribution. 



This symposium deals with the mechanisms which are responsible for the 

 late somatic effects of ionizing radiation; emphasis was placed on the dis- 

 cussion of the nature of early biological changes (i.e. occurring within days 

 of irradiation) which are responsible for the eventual appearance of cancer, 

 leukaemia and non-neoplastic late effects, particularly those which bring 

 about the observed shortening of life-span. At the present time very little 

 is known about the aetiology of these disturbances. Somatic mutations, 

 activation of latent viruses and anatomical and morphological changes (e.g. 

 in blood vessels) due to cell killing at the time of irradiation, as well as 

 modification of the structure of extra cellular connective tissue components 

 may all contribute. In radiation induced cancer, one of the many un- 

 resolved problems is whether the cell (or cells) which starts the tumour 

 must actually be irradiated or whether radiation damage in the surrounding 

 tissue can initiate malignancy. 



A knowledge of the cellular basis of late effects of radiation is of more 

 than academic interest since only by understanding mechanisms will it be 

 possible to predict with confidence the magnitude of the hazards to human 

 beings from low doses of radiation. Late somatic effects are, of course together 

 with genetic changes, the principal hazards of the peaceful uses of atomic 

 radiations. In deciding the level of exposure that is acceptable, consider- 

 ations of the late somatic effects are predominant. It has frequently been 

 pointed out that prediction of the risks from very small doses of radiation 

 and, in particular, the problem of whether there is a threshold cannot be 

 decided from animal experimentation even if attempted on a vast scale. 

 Only an understanding of the basic mechanisms will make it possible to 

 decide the shape of the dose response curves at low doses. These consider- 

 ations seemed to justify devoting a whole symposium to this narrow and 

 relatively unexplored field. We hoped to gather a group of some thirty 

 scientists actively engaged in this field and I believe that with the exception 



vii 



