Total Energy Absorption in Radiotherapy 203 



TABLE II 



Effect on Volume Dose of Increased FSD (Carcinoma of Esophagus, 

 40 Centimeters FSD and 100 Centimeters FSD) 



200 kv 

 1.5 mm Cu HVL Tumor dose = 6,000 r 



Field size 15 X 4 cm^ Eight fields 



Total Energy Absorption 



92 92 



3,400 X 60 X 126 X — — rcm^ 2,800 X 60 x 101 x —- r cm^ 



76.3 76.3 



= 3.11 X lO'rcmS — 2.05 X 10" rcm3 



(125%) (100%) 



Field Area 



The volume dose is almost proportional to the field area. 



Focus-Skin Distance 



A comparison is made in Table II of the volume dose using 

 two techniques for treating carcinoma of the esophagus, the only 

 difference between them for a given tumor dose being the dif- 

 ference in FSD. These estimates are based on Happey's 



