Histological Analysis of Radiation Effects 173 



degree of differentiation of such specimens shows that, cHnical 

 conditions and treatment methods being equal, the results of 

 radiotherapy tend to be more satisfactory in the cases with 

 more differentiated tumor tissue.^- The physical factors of radia- 

 tion, such as time, dose, dose rate, and type of ray, which are 

 most likely to elicit differentiation in cells with such potencies, 

 are as yet little known and understood. It appears feasible that 

 favorable results may be obtained with changes in technique 

 in those groups of tumors which so far have proved refractory 

 to treatment. 



There are various limitations in the application of the quantita- 

 tive histological method of analysis of radiation effects in indi- 

 vidual cases of malignant disease. Thus, conclusions about a 

 favorable response to treatment must be limited to the reaction 

 of the growth in the treated area, presupposing that the radiation 

 energy was fairly uniformly distributed in this area. In spite 

 of cures in the treated area, the clinical issue may, of course, 

 be compromised by the presence of untreated metastases, or even 

 by fatal hemorrhages due to radiation damage inflicted on the 

 vascular apparatus. Certain types of cancer are systemic dis- 

 eases with local manifestations, and obviously the cure of one 

 of these manifestations cannot prevent the formation of new ones 

 which may even arise in neighboring precancerous lesions. 



Conclusions 



To summarize : the quantitative histological examination of 

 serial biopsies of human tumors provides a useful guide in the 

 evaluation of the therapeutic result in individual cases. As a 

 research method, it facilitates the analysis of the "radiosensi- 

 tivity" of an individual growth, makes possible the study of the 

 factors influencing the response of a given tumor to a given type 

 of treatment, and provides a basis for the understanding of 

 radiation effects on tumor tissue of different types and for the 

 better knowledge of the natural history of malignant diseases. 

 The combination of such knowledge with relevant data con- 

 tributed from radiobiological research is the necessary require- 



