DISCUSSION 37 



If one superimposes fields so as to cover an area of the dimensions met with in 

 practice, he will find that the distribution becomes poorer, by addition of the 

 doses between surface and maximum. 



Wilson : 



Cross fire with electron beams, will, of course, not influence the scattering at 

 the end of the range inherent in electron beams. This is also true for protons, 



Tobias: 



It is admirable that Wilson was able to calculate the exact range and ioniza- 

 tion properties of high-energy protons and predict their radiological application 

 some 2 years before such beams were experimentally produced. His ideas in- 

 spired the group in Berkely to carry out the initial experiments. We have now 

 some 2 years of experience with 190-mev deuterons and their effect on animals. 

 I can state that, as far as acute lethal effects of this radiation on mice go, they 

 are very similar in timing and energy dosage to the effects of 200-kev7 x-rays. 

 Initial application to experimental mouse-tumor therapy convinced those doing 

 the work that such beams can be beneficial in deep tumor therapy far beyond the 

 range of usefulness of low-energy x-rays. It is clear, however, that before 

 large-scale-human applications are made, one should find out much more about 

 the effects of local irradiation of animals, acute and delayed, and about biologi- 

 cal effectiveness of the different portions of these beams which have different 

 rates of energy loss in tissue. In these connections the high-energy ion beams 

 have become useful tools in radiobiology, in an extended study of the physio- 

 logical changes produced by localized irradiation. May I suggest that Bond, 

 who has been working on this problem, make a comment. 



Bond: 



The nature of the work that Miss Marguerite Swdft and I have been doing 

 with Tobias is such that the reporting of most of it will be more appropriate 

 during later discussions in the symposium. A few remarks, however, are per- 

 tinent to the possible use of high-energy particles in radiation therapy. 



We have taken advantage of the lack of lateral scatter from the deuteron 

 beam to achieve highly selective irradiation in the rat. The beam traversed the 

 entire width of the animal, and thus we took no advantage of the increased ion 

 density at the "tail" of the Bragg curve. 



A good deal of difficulty in reproducing results was encountered when irradia- 

 tion was confined to portions of the abdomen. This led us to determine, by 

 means of sectioning frozen animals, exactly which organs were contained in the 

 volume of tissue through which the beam passed. With rats of nearly identical 

 body weight, a good deal of variation both in the type of organ and in the 

 fraction of a given organ contained in the irradiated volume was noticed; hence 

 the possibility of accurately localizing such irradiation to a given body region 

 by means of external markings seems remote. 



In addition, it was noted that many animals surviving the acute effects of 

 irradiation localized to the abdomen exhibited, within about 2 months, discrete, 



