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Applied Biophysics 



FIG. 4b. Dose Distribution of Two Fields of Type Illustrated in Figure 4a, 

 Arranged at Right Angles, the Positions of the Thick Edge of the Wedge 

 Being Contiguous. The Distribution Is Fairly Uniform Through the Block 

 OF Tissue Enclosed i:y the Fields and Declines Rapidly Outslde (Ellis and 

 Miller '') 



Methods of Study of the Dose Distribution from a 

 Number of X-rav Beams 



Most X-ray treatments require for their study the summation 

 of the dose distrihutions of several beams. If the axes of these 

 beams are coplanar, the distribution in that plane can be found 

 by superimposing, in the correct relative positions, isodose charts 

 drawn on transparent sheets, and summing them in succession 

 at the points of intersection of the curves. A convenient method 

 is that of Ungar,"^'*^ who cut blue-base film (discarded diagnostic 

 X-ray films freed from gelatin) to the shapes of isodose curves, 

 and stacked them, so that points which had, for example, per- 

 centage dose rates of 60 to 70 had six thicknesses of film below 

 them. Put on a viewing box, the depth of color showed the 



