Total Energy Absorption in Radiotherapy 



201 



Mayneord and Clarkson ^^ also constructed a wax model for 

 making measurements to estimate the volume dose when the 

 whole body is irradiated. The actual measurements were made 

 in slabs filled with the suggested powder mixture of Spiers,^ ^ 



400 



FIG. 6. Relation of volume dose to field area for irradiation of the pelvis. Inset 

 curve shows relation for rontgen dose measured without scatter, which is linear up 

 to 200 square centimeters. (From Boag.i) 



and estimated both by the average-dose method and by planimeter 

 measurements of the areas between isodose curves in the body- 

 section (figure 8). Their results are represented graphically in 

 figures 9 and 10, which show the volume dose in gram-rontgens 

 per rontgen to the surface of the body (70 kilograms ) for various 

 half-value layers. It is seen that there is a rapid rise up to 

 HVL = 0.2 millimeter Cu (= about 100 kilo volts with 0.15 

 millimeter Cu filter) followed by a less rapid change. 



