A QUANTITATIVE DESCRIPTION OF LATENT 

 INJURY FROM IONIZING RADIATION* 



H. A. Blair 



Department of Radiation Biology, University of Rochester 

 School of Medicine and Dentistry 



Abstract— A group of hypotheses previously discussed by the writer to account for the kinetics 

 of radiation injury in mammals is reviewed. That radiation injury is proportional to dose, 

 is partly irreversible, and that irreversible injury adds to new acute injury to produce lethality, 

 appear to be vaHd. Recovery is not a single process for the whole animal but proceeds at 

 different rates in different regions. The lethal threshold diminishes, presumably to zero, in 

 old animals but not in proportion to life expectancy throughout adult life; rather it changes 

 more slowly at first and then more rapidly. Irreversibility of injury differs with different 

 radiations. With x- or gamma-rays it appears to be a similar fraction with doses smaller 

 than about 100 r, but increases with larger brief single doses. The data in general are not 

 sufficiently extensive and accurate to test hypotheses critically. 



Over the past several years (1, 2, 3, 4, 5) I have discussed the adequacy of 

 certain hypotheses to provide an empirical mathematical description of radiation 

 injury and its effect on the duration of life. These hypotheses have been fairly 

 successful in outlining a broad picture of radiation injury, in correlating many 

 of the data and in suggesting critical experiments. It has become obvious, 

 however, that they are deficient in some details and require amplification or 

 revision. I propose at this time to discuss those changes in these hypotheses 

 which appear to be necessary and also to point out some of the areas in which 

 the data are inadequate to form the basis of quantitative correlations. 



The hypotheses in question are as follows: 



(a) The total injury produced by ionizing radiation is proportional to the 

 dose. 



(b) This injury is reparable in part and irreparable in part. 



(c) Recovery from reparable injury occurs at a rate proportional to its 

 magnitude. 



(d) In consequence of (a) and (b), irreparable injury accumulates in pro- 

 portion to total dose. 



(e) Reparable and irreparable injury add in all proportions and death 

 occurs when their sum attains a level which is proportional to the 

 remaining life expectancy. 



The injury defined here is a latent form observable at present only in terms 

 of additional radiation dose. With acute exposures this injury has largely 

 disappeared in most species before the clinical syndrome of radiation sickness 

 has fully developed. There is presumably a quantitative causal relationship 



* This paper is based on work performed under contract with the United States Atomic 

 Energy Commission at the University of Rochester Atomic Energy Project, Rochester, 

 New York. 



331 



