Advanced Physics for Brachytherapy 2018

2. inhomogeneities

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

ACE scales attenuation and absorption voxel-wise according to:

The same recursive equation applies BUT: • additional input is required to calculate η 1sc , χ 1sc : the energy spectrum of 1sc photons generated at each point. This is taken from calculations in water so: • the scaling is APPROXIMATE and its accuracy deteriorates as materials yield different 1sc spectrum from water (as Z increases due to coherent & photoelectric phenomena-x ray fluorescence and S(x,Z))

m

   

   



sc w m bmb , 1    

=

=



sc b







1

w

m

   

   



sc en w m BmB , 1    

=

=



sc b







1

w