Major Radiobiological Concepts and Effects 



of Ionizing Radiations on the 



Embryo and Fetus 



Roberts Rugh 



Radiological Research Laboratory, 

 Columbia University, New York, New York 



Introduction 



As a radiobiologist, it is appropriate to initiate this symposium witti a few 

 general statements regarding the biological eflfects of ionizing radiations. We 

 are concerned with ionizing radiations, not ultraviolet or infrared radiations. 

 Ionizing radiations result in the excitation or loss of an electron from an 

 atom, causing an unstable situation, whether it be in an atom of an inani- 

 mate or animate object. Such imbalance can be brought about by alpha or 

 beta particles, by x-rays or gamma rays, or secondarily by neutrons. The 

 ensuing physical imbalance results in a chemical change which, in turn, may 

 effect a demonstrable biologic adjustment. While the ionization may be 

 immediate or instantaneous, and is in most cases undetectable by the nervous 

 system, the evidence of the biologic adjustment may take decades. 



Radiations are so potent that the ionization of one molecule in 10,000,000 

 is sufficient to kill almost all organisms. It matters not whether the ionization 

 is brought about by any of the different qualities of radiation, the basic 

 biologic reactions are the same. However, the total dose absorbed and the 

 dose rate are indeed important. There is a total absorbed dose which cannot 

 be sui-\'ived, and there is a dose rate so small that it can be tolerated. In all 

 properly controlled radiobiologic experiments the ion density, the dose rate, 

 and the total absorbed dose must be determined and recorded. In reporting 

 radiobiologic experiments it should be made clear what specific organism, 

 organ, tissue, or even cells are concerned, because tolerance is not uniform. 

 This does not contradict the statement that the biologic reactions to ionizing 

 radiations are basically the same. It does emphasize the fact that tolerance, 

 restitution, and repair are properties which vary with the large variety of 

 differentiated tissues. Organisms vary during their lifetime in their reaction 

 to absorbed ionizing radiations, even as do cells during their process of dif- 



