38 BEAMS OF HIGH-ENERGY PARTICLES 



localized, annular, tumor-like masses situated in the small bowel. These appar- 

 ently are of the type previously described by Shields Warren and seem to rep- 

 resent an exaggerated fibroblastic reaction to local tissue destruction and 

 infection. This reaction was observed at doses of the order of 2000 rep. 



Brues: 



It should be emphasized, for the enlightenment of those w^ho have not been 

 concerned (as have practicing radiotherapists) with the locahzation of structures 

 within the human body, that it is at times very difficult to know where they are 

 or to be sure they stay there. Some attention will need to be paid to physical 

 and other means of establishing the positions of tumors and other structures 

 inside the human body before extreme depth localization of radiation will, in 

 general, be profitable. 



Failla: 



Definition of the tumor volume clinically is very difficult. In practice it is 

 necessary to radiate a margin of normal tissue in addition to the volume thought 

 to contain the tumor. For this reason highly defined beams cannot now be used 

 to maximal advantage. The use of such beams must await solution of the 

 problem of definition of tumor volume. 



Friedell: 



There appears to be some overemphasis on beams by localized radiation to 

 small volumes a few centimeters or even a few miUimeters in diameter. Local- 

 ization has been practiced by radiobiologists and radiation therapists for some 

 time by the use of interstitial radiation in the form of radon or radium needles, 

 cobalt pellets, interstitial colloidal gold, etc. It is doubtful that localization 

 becomes critical, at least from the point of view of specific biological reactions, 

 until we can localize radiation to the small volumes which correspond to cells or 

 portions of cells, such as the nucleus or the nucleolus within the nucleus. 



Low-beer: 



Attention should be called to two factors in the use of any type and energy of 

 ionizing radiation in clinical therapy. One is the time factor between the ex- 

 posure and the reaction chosen for observational inferences. Morrison said that 

 he was describing only in the first one-hundredth of a microsecond following 

 radiation exposure. Fano said that he is interested in the subsequent fractions 

 of a second. The clinical radiologist must stay with his patient for weeks, 

 months, and often for years. Both early acute and late chronic radiation re- 

 actions are manifested by the composite tissues of the patient. The two reac- 

 tions differ in appearance and also in significance. For the same quantity of 

 various types and/or energies of radiation the early reactions may be similar, 

 exceptions granted. The acute reaction gradually increases, reaches a peak, and 

 disappears again gradually in a period varying from 3 to 10 weeks. Acute ra- 

 diation reaction is a reversible process. Reactions months or years later— that 



