Dose 2016

Derivation of formalism to convert ionisation in plastic to dose to water Converting ionisation measurement in plastic to dose in water

Phantoms irradiated with the same MV photon beam

In water at a reference depth

In solid plastic at an equivalent depth

z

z

eq

ref

s

 

 

sQ, S k N r z M r z D air ρ ⋅ ⋅ ⋅ ⋅ p

2

+

   

   

   

) ( ) ( ⋅    

w

SSD

z

ref r S r S eq sp,

µ

(

)

ref

=

⋅

⋅

⋅

(

)

w

en

eq

,

,

β

Qw,

ref

ref

ref eq Qs,

Qw, D,

QQ,

s

+

w

 

 

SSD

z

ρ

o

o

S

⋅

ref

sp,

p

ref

s

ρ

wQ,

air

Phantom dose conversion factor for the ionisation chamber

( )

( ) ref

k k N z M z D

=

Qw,

eq Qs,

Qw, D, o

QQ,

Qw, s,

o

Seuntjens et al, 2005, Med.Phys. 32 pp2945-