Histological Analysis of Radiation Effects 163 



These examples, as well as the rather vague and general 

 statements composing the "nadiosensitivity tables" of 

 tumors,^' ^^' ^^' ^^ illustrate the difficulties encountered in an 

 analysis of the factors determining the radiosensitivity of indi- 

 vidual growths or groups of tumors, and of the likely response 

 to any particular type and dose of radiation. Although some 

 general principles have been elucidated by radiobiological re- 

 search, their application to the practice of radiotherapy is handi- 

 capped by the hetergeneous collection of nosological entities 

 lumped under the term "cancer," ^ and also by the essential 

 differences in biological characters and reactions of much of the 

 biological material chosen for experimentation and of maligant 

 cells and tissues. 



The study of the local response of various types of neoplastic 

 diseases to radiation can be undertaken only by investigating 

 the actual response of individual tumors to treatment, i.e., by 

 examining serial biopsies taken before, during, and after treat- 

 ment, and by correlating the histological with the subsequent 

 clinical and pathological findings. It is useless, however, to com- 

 pare biopsies taken at random with one another, since owing to 

 their localization in the tumor, i.e., whether near the necrotic 

 center or the well-vascularized growing edge, the specimens 

 from the same tumor may vary as to the proportion of old and 

 young foci included. To obtain comparable results in serial 

 biopsies of an individual case, sections should be taken from the 

 growing edge of the tumor, and in such specimens only the 

 young areas should be chosen for a detailed examination of the 

 reaction of the tumor tissue to treatment. Young foci alone 

 contribute to the further expansion of the tumor ; they possess 

 the greatest developmental potentialities in any given malignant 

 growth, and are best able to react to, and to recover from, the 

 effects of treatment. 



If these precautions are taken, reliable and comparable 

 "samples" of young foci in the tumor can be obtained. In a' 

 series of about 20 surgical and pathological specimens of various 

 carcinomata, a number of small pieces of tissue equivalent to 

 biopsy sections were taken from the growing edge, comparable 



