244 FACTORS INFLUENCING CELL RADIOSENSITIVITY 



1.0 



0.7 



0.5 



0.3 

 0.2 



I 0.1 



0.07 

 0.05 



0.03 

 0.02 



0.01 



0123456789 



Dose 



Fig. 1. Theoretical survival curves for different values of the multiplicity from 1 to 



100. 



This shows that the sensitivity of infected cells decreases regularly 

 as the number of intracellular particles is increased. This decrease 

 is not very pronounced because, in increasing the number of particles, 

 the total volume they offer to radiation is correspondingly increased. 

 Thus, for example, to injure 90 per cent of the cells one needs a dose 

 3 times as large when they contain 100 particles as when they contain 

 only 1 particle. 



Formula 1 and the group of curves derived from it define, in the 

 present case, the quantitative influence of the number of units involved 

 on cellular sensitivity. 



