Advanced Physics for Brachytherapy 2018

1. I need to be efficient, angular discretization

How can I relax the demand on S N

without ray effects?

The LBTE is linear so assuming:

P







unc

) ˆ,

rg

( gp r

r coll

)ˆ,(

  = 

+



)ˆ,(

g

,

p

=

1

For any direction, we can split our system of equations in two:



P

 

gpq

,

unc g

unc g gt =  +     =

ˆ



(

−

)

)1(

pr r

,

p

1 4



 P

, coll scat g

, unc scat gpq ,

coll g

coll g gt

ˆ

=  q

 

+



+

)2(

,

p

=

1

Equation (1) for the primary (uncolided) part of the fluence can be analytically solved!!!

I can ray-trace the solution for the spectrum of primary photons through the geometry and arrive at very quick and accurate: initial guess and q scat,1,n 0 ) ( ,1 =  iter rn  Then I proceed to solve the system of equations (2) for the collided fluence to refine my solution with the higher orders of scatter

This is known as the 1 st scatter source method