Advanced Physics for Brachytherapy 2018

The basic equation is the LBTE

) ˆ, , ( ,   ErE 

Let

be the angular fluence (dΦ/dΩdE=dN/dAdΩdE) denoting the number of photons in phase space element , i.e. passing through a voxel of area dA normal to located at , with wιthin Ω and Ω+dΩ and E between E and E+dE. ) ˆ , ,(  Er  r   ˆ

 ˆ

At any part of this “phase space”, conservation of E dictates particle density balance.

The net flow of photons through a phase space cell equals:

, E rE  ,

ˆ



(

=   )ˆ

 ˆ

,



photons scattered in it from all others (E’, Ω’)

ˆ , ,

q

r scat

 E

(

)

+ photons emitted by a source in it

q

E



)ˆ, (

)   −

p

+



(

pr r

4



- photons absorbed or scattered out of it





) ˆ,

rt

,   − Er E E (



, ) ,(

L.B.T.E.