Dose Course 2018_Flipping book

Stoichiometric calibration: An improved approach

U. Schneider et al PMB 1996

Relative proton stopping power

Calculate Relative Electron Density:





(

)

I cm  2 2

2

2



N



 = − − − − 2 

2 log

1

g

e

m

 =



=





K





(

)

e

s

e

e

water

water g

2 2

2







N

m 2 log

c

I

1

e

w

Using chemical composition:

Zw NN N

i g

  i i

=

=

g

A

A

i



Rutherford et al 1976

1000 =

H



~



 KN

ˆ

w

ph

.3

62

coh

86.1



=



+

K Z K ZK +

A ZN

) , (

g

By making measurements of H for different tissue substitutes of known composition one can get a fit of data to derive values for K ph/coh/KN which characterize the CT scanner

From this can plot a curve to predict H for range of tissues substitutes and real tissue