J. H. MARTIN AXD G. MULLER 



Radiation scattered outside the defined field has l^een studied- at the two 

 depths of approximately 5 cm and 10 cm. The result of a similar study is 

 sho\vn in Figure 2 and it will be seen that the amount of radiation falls off 

 approximately logarithmically with distance from the edge of the field. 



In Figure 3 is plotted the amount of scatter at a given point against radiation 

 quality from which it will be seen that the scatter increases with radiation 

 quality reaching, however, a maximum about a half value layer of 2 -5 mm of 

 copper, that is, in the deep therapy range. Thus, as far as the diagnostic 



H.VL57mm Al 



A-25mm Al 



305 mm Al 



i_ 2-35mm Al _ 

 VA8mm Al 



2 A 6 8 10 12 



Depth cm 



Figure 1 



X-ray region is concerned, higher kilovoltage techniques involve more 

 scattered radiation. 



The skin doses appropriate to each type of examination which have been 

 used are those listed in Table 1. These are taken mainly from the work of 

 one of us (J.H.M.) and are listed together with those given by the Inter- 

 national Commission on Radiological Protection^ The percentage of the 

 surface dose reaching the region of interest has been determined from the 

 data of Trout, Kelley and Cathey^. The dose thus reaching the bone is 

 corrected for absorption by the hard shell. The appropriate absorption 

 coefficient is obtained from the work of Spiers^ using the radiation quality 

 data o{ Figure 1. The bone-marrow dose is then obtained by correcting this 

 figure for the emission of electrons from the hard bony surface after the 

 method developed by Spiers^. This latter correction does not exceed 10 per 

 cent. The bone-marrow distribution used is derived from the work of 



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