Advanced Physics for Brachytherapy 2018

2. inhomogeneities

Medium can be of varying material (different elemental composition and Zeff)



1 )( 1

r





) ,(

This affects cross sections and hence B θ ,b θ

sc dR

r sc 

) ,( 1h =

=

exp(

−



) , 1 



sc

, 1 sc en r 

2

dV R sc

1 R sc

dr 

1



1 )( 1

sc dR

=

exp(

−



) , 1 



Can’t we scale the kernel? Yes and different approaches have appeared in the literature.

sc

, 1 sc en r 



2

dr en 

1(

−

)



B

) rb

exp(

−





=

2

r

ACE scales attenuation and absorption voxel-wise according to:



1 )( 1

sc dR

B

=





 , 1 sc en d en





m

1(

−

)

   

   







sc

1

,



m

b b =

b

=



m

sc







1

b

=







sc



 , 1

w

w

m

   

   



en sc



1 ,



m

B Bm 

=

= 



sc





1





w

w