36 BEAMS OF HIGH-ENERGY PARTICLES 



Availability and Cost 



Electrons and photons for radiological work are cheapest. Betatrons 

 of adequate energy (about 30-50 mev) are commercially available and 

 cost about $100,000, installed. Such machines are not much larger than 

 conventional x-ray machines. Linear accelerators which are being 

 developed to accelerate electrons may be even cheaper. 



Medically useful sources of protons would cost at least $1,000,000. 

 As the technology improves, the cost of commercially available synchro- 

 cyclotrons may come down. Per roentgen, the cyclotron may be 

 cheaper, because of its larger beam. This suggests the use of cyclotrons 

 at centers where one cyclotron beam could be piped to, and readily serve, 

 say as many as 100 treatment cubicles at once. 



REFERENCES 



1. Koch, H. W., D. W. Kerst, and P. Morrison, Radiology, 40: 120, 1943. 



2. Skaggs, L. S., Radiology, 53: 868, 1949. 



3. Wilson, R. R., Radiology, 47: 487, 1946. 



4. Bohr, N., Phil. Mag., 30: 581, 1915. 



5. Wilson, R. R., Phys. Rev., 71: 385, 1947. 



6. Tobias, C, and P. Auger, private communication. 



DISCUSSION 



QUASTLER : 



I am afraid that two complications must not be omitted from a consideration 

 of high-energy rays. One is of a biological nature. It is true that the elementary 

 responses to all ionizing radiations are about the same. However, the relative 

 efficiencies of two kinds of radiations, in producing different responses, are not 

 constant. Thus, if doses of two kinds of radiations are matched with respect to 

 one response, the other response might be ehcited in a quite different strength. 

 For instance, doses of different radiations, matched so as to produce equal per- 

 centages of killing in plant seedUngs, will not produce equal amounts of stunting 

 in the survivors. In general, if one considers the whole complex of responses 

 ehcited by irradiation of a complicated organism, he will find that the relative 

 strength of the various responses, and hence the total picture of the reaction, 

 depend on the quality of radiation used. 



The other complication enters into the evaluation of depth-dose charac- 

 teristics. It is not realistic to consider a single beam only; one has to study 

 systems of cross firing. Under this point of view, the large exit dose of high- 

 energy photons is not much worse than the high entrance dose of high-energy 

 electrons: besides, the photons have the advantage of much better collimation. 

 The depth-dose curve of high-energy protons looks exceedingly attractive; but 

 as a rule we do not shoot at areas 2 mm in diameter, situated 10 cm in the depth. 



