Dose Course 2018_Flipping book

calculation techniques:

Penumbra effects: • electron transport effects – automatically by the kernel • collimator transmission and finite source occlusion effects

• should be considered during fluence modelling (dosimetric leaf gap addition not sufficient) • can also be approximated with a field edge blurring convolution of the primary part, example (in dose domain, direct blurring of idealized collimated fluence also possible ):

a r

b r

−

−

A e

B e

p

z

z

( ) , r z

z

z

=

+

r

r



z

coll



2

r

a r

−

−

A e

1

z

2



z

e



z

z z z −

2

r



coll



 = 

z

z

coll

projected Gaussian source distribution

A Ahnesjö et al (1992) Med Phys 19, 263-273