Sec. 24.4] CRITIQUE OF BIOLOGICAL APPLICATIONS OF ISOTOPES 513 



in a biological system. However, its radioactivity can have decided effects 

 when the isotope is present in sufficiently high concentration. In terms of the 

 effect of ionizing radiation, its effect may be profound. 



Radioactive isotopes have been used in a number of studies on the effects of 

 ionizing radiation on biological systems. In particular, interest has been 

 focused on those isotopes which can be administered in a form that will be 

 selectively localized in specific parts of such systems. The basis for the use 

 of radioisotopes in therapy lies in the phenomena of differential concentration. 

 Dosimetry of radioisotopes has already been discussed in Chap. 16. 



