Advanced Physics for Brachytherapy 2018

Input:

1. I need to be efficient

D

distr.

•

prim

• Source primary spectrum for calculating S 1sc • 1 st scatter kernel • Individual voxel density data Assumptions: CC: • S 1sc does not vary with θ within ΔΩ (Bθ, bθ constant along transport line) • S 1sc generated, emitted and absorbed along transport line and: • S 1sc generated per unit r is constant within the same voxel (scerma does not vary considerably within voxels)

An efficient algorithm for the calculation of dose from 1 st scatter: • Calculate S 1sc distr., from D prim distr. • Choose ΔΩ: optimal number of directions • Construct lattice of transport lines (B θ , b θ per ΔΩ, relative to direction of primaries) • Ray-trace along each transport line for Δr i and iteratively calculate D i • Sum D i from all transport lines

i

1 − 

S ρ [1 exp( 1sc,i-1 i-1

B

b r − − 

b r − − 

)][1 exp(

)]

i

i





b −

1



D D 1sc i = 

+

D

=

+



1sc 1 i

i

i i →

− →

1sc

b

ρ

Δr

i





i

i

1



S { 1sc,i

b r

[1 exp(  − − −  b r

)]}

i

i





B

+



b

b ri 



