198 



Applied Biophysics 



a, the volume dose throughout the sphere was calculated by 

 Mavneord to be 



where F = 2a -1- 



a' 



8.3 X -^^^ X F per mgh 



a-\- c 



loge 



a 



c being the distance of the point source of radium from the center 

 of the sphere, and the relationship of F to c/a is given in figure 3, 

 taken from Mayneord. Examples of volume doses are given 

 for certain situations and techniques met with in practical 

 radium therapy. 

 For example : 



1. In treating a carcinoma of the maxillary antrum with a 

 dose of 3,000 mgh, the volume dose is assumed to be that 

 for a sphere of radius 9.8 centimeters and of mass approxi- 

 mately 4 kilograms with the radium relatively centrally 

 placed : 



2 = 3,000 X 0-89 =: 2.7 megagram-rontgens, 



0.89 being the graph reading (see figure 2). 



1100 

 1000 

 «k 900 

 ^ 800 

 Z 700 

 « 600 



s: 500 



^ 400 

 Z 500 

 J 200 

 - 100 



II 



100 



90^ 



80 > 



70 1 



60 "^ 



5 ° 



4 ^ 



3-0 S 

 2 ■ 



10 



500 1000 2000 3000 4000 



MASS IN GM= VOLUME IN CZ. 



5000 



FIG. 2. Integral dose per mgh for point sources near the center of an absorbing 

 mass of known volume and mass. (From Mayneord. !■*) 



2. In treating carcinoma of the cervix uteri with a dose of 

 6,000 mgh, the integral dose is calculated as about 9.8 



