Total Energy Absorption in Radiotherapy 211 



as distinct from local effects, however, might be due to the local 

 effects of radiation. Thus, the local effect of radiation on the 

 mouth and esophagus might have a profound effect indirectly 

 on the general nutrition, the lighting-up of local infection might 

 also have a marked general effect, while local edema in such 

 specialized structures as the lung and brain might have a marked 

 effect on general well-being. Moreover, the variable structure 

 of the human body makes estimates of the usual accuracy de- 

 manded in physics almost impossible. In addition, different 

 regions of the body differ in sensitivity, while the variation from 

 one human being to another, due to metabolic, physical and 

 psychological differences, conspires, with the influences men- 

 tioned above, to make difficult the correlation of biological 

 phenomena with volume dose, Nevertheless, some attempts 

 have been made. 



The Volume Dose Limiting Radiation Technique 



In table IV the volume dose for lung and esophagus of about 

 30 megagram-rontgens in one month is near the limit of what 

 the patient can tolerate. Levitt,^ ^ in an account of trunk-bath 

 radiation, finds that the maximum dose to the surface which can 

 be tolerated is 1,500 r (measured with backscatterj, though 

 treatment under such conditions has not to be stopped because 

 of local effects, e.g., on skin. This corresponds to a volume dose 

 of about 30 megagram-rontgens in 6 weeks. Phillips '^^ found 

 that 40 megagram-rontgens was less than the maximum dose that 

 could be tolerated in about 4 weeks in treating a rectum. At the 

 London hospital, I find that treatment to the whole abdomen 

 permits of a volume dose of about 40 megagram-rontgens in 

 3 weeks, so that it appears that a patient will tolerate a large 

 volume dose to a smaller part of the body more readily than to 

 a large part. 



Apart from therapeutic conditions such as these, it does not 

 seem from table 1\ that the volume dose is likely to limit tech- 

 nique as at present developed. It is possible to imagine condi- 

 tions, however, under which such limitation might occur. Sup- 



