Dose Course 2018_Flipping book

Small fields: relative dosimetry - field size factor, S cp

measurement with an ionisation chamber fluence perturbation

A

w

   

   

(

)

(

)

) S z AM zAM ref ,    ρ ref

  

A,z D ref

,

  A A p det

( )

w

AS =

=

cp

(

)

(

z AD

,

ref

w

ref

ref

ref

air

A

ref

Challenge: perturbation factors

A : field size (aperture) z ref : reference depth