86 



RADIATION BIOLOGY 



located at equal depth below the surface receive equal amounts of energy, 

 provided that the dimensions of the surface uniformly exposed to radia- 

 tion are large as compared to the penetration of the radiation. Figure 

 1-51 and Table 1-8 show how the escape of radiation sidewise, beyond the 



PER CENT OF SKIN DOSE 

 100 



PER CENT OF AIR DOSE 

 136 



180 kv CONSTANT POTENTIAL, 

 0.5 mm Cu FILTER 



100 cm2 

 50cm DISTANCE 



Fig. 1-51. Charts of X-ray dose distribution within and at the edges of a beam 

 traversing tissue. {Glasser, 1950.) 



Table 1-8. Percentage Depth Dose" for Various Sizes of Irr.\diated Area 



(Quimby and Focht, 1943) 



" Depth dose — 100 X dose at stated depth /dose at surface. Values are for 1000-kv 

 X rays (half-value layer 3.8 mm of lead or 10.3 cm of Presdwood) and 70 cm focus-skin 

 distance. 



limits of the region directly exposed, affects the absorption at various 

 depths, under different circumstances. 



The complications due to scattering effects are minimal in the penetra- 

 tion of heavy charged particles. 



