Dose Course 2018_Flipping book

Factor-based dose calculations: basic dosimetric quantities

In-air output ratio or output factor in air, Sc

Is the ratio of primary collision water kerma in free-space K p per monitor unit (MU) between an arbitrary collimator setting c and the reference collimator setting c ref at the same location on the beam’s central axis:

Also known as:

(

)

K

ref dc

M ;

( ) cS c =

p

Mini-phantom output ratio

(

) M d cK ref

;

Collimator scatter factor

p

ref

Head scatter factor

d

ref

c

ref

Sc quantifies fluence variations with collimator settings that can be used in beam modelling and dose calculations.



Usually d

= 10cm and c

=10cm

en

K

E

=



d



ref

ref

spectrum primary

p

E



Report pf AAPM TG106: Accelerator beam data commissioning, Med Phys, 35(9), 2008 AAPM TG 74 report, Med Phys 36 (11), 2009